DC-DC Converter Applications - RS Componentsdocs-asia.electrocomponents.com/webdocs/04ba/0900766b804bae0a.pdfDC-DC Converter Applications DC-DC Converter Applications Terminology The

DC-DC Converter Applications DC-DC Converter Applications

www.recom-international.com 265

Terminology 266

Calculation of heatsinks 266

Efficiency at FulI Load 266

Input and Output Ripple 266

Input to Output Isolation 266

Input Voltage Range 266

Insulation Resistance 266

Isolation Capacitance 266

Line Voltage Regulation 266

Load Voltage Regulation 266

Mean Time between Failure (MTBF) 266

Operating temperature range 267

No Load Power Consumption 266

Noise 267

Output Voltage Accuracy 266

Switching Frequency 266

Temperature above Ambient 266

Temperature Drift 266

3V/5V Logic Mixed Supply Rails 273

Conducted and Radiated Emissions 277

ConnectingDC-DC Converters in Parallel 269

ConnectingDC-DC Converters in Series 269

EIA-232 Interface 273

EMC Considerations 274

Filtering 269

Input Voltage Drop-Out (brown-outs) 272

Interpretation of DC-DC Converter EMC Data 276

Isolated Data Acquisition System 274

Isolation 268

Isolation Capacitanceand Leakage Current 270

LCD Display Bias 273

Limiting Inrush Current 270

Line ImpedanceStabilisation Network (LISN) 277

Line Spectra of DC-DC Converters 278

Long Distance Supply Lines 272

Maximum Output Capacitance 270

No Load Over Voltage Lock-Out 272

Output Filtering calculation 270

Overload Protection 271

Power Supply Considerations 276

Recommended Values for Paralleled DC-DC Converters 269

Settling Time 270

Shielding 278

Temperature Performanceof DC-DC Converters 278

Transfer Moulded SurfaceMount DC-DC Converters 279

Adhesive Placement 280

Adhesive Requirements 280

Cleaning 281

Component Alignment 279

Component Materials 279

Component Placement 279

Production GuidelineApplication Note 279

Recommended Solder Reflow Profile 280

Solder Pad Design 279

Solder Reflow Profile 279

Custom DC-DC Converters 281

Powerline – Definitions and Testing

Ambient Temperature 288

Break-Down Voltage 288

Current Limiting 287

Efficiency 286

Fold Back Current Limiting 287

General Test Set-Up 284

Input Voltage Range 285

Isolation 288

Line Regulations 285

Load Regulation 286

Operating Temperature Range 288

Output Ripple and Noise 286

Output Ripple and Noise(continued) 287

Output Voltage Accuracy 285

Output Voltage Trimming 289

PI Filter 285

Storage Temperature Range 288

Switching Frequency 286

Transient Recovery Time 287

Temperature Coefficient 288

Voltage Balance 285

Content


TerminologyThe data sheet specification for DC-DC con-verters contains a large quantity of infor-mation. This terminology is aimed at ensu-ring that the user is interpreting the dataprovided correctly and obtaining the neces-sary information for their circuit application.

Input Voltage RangeThe range of input voltage that the devicecan tolerate and maintain functional perfor-mance.

Load Voltage RegulationThe change in output voltage over the spe-cified change in output load. Usually speci-fied as a percentage of the nominal outputvoltage, for example, if a 1V change in out-put voltage is measured on a 12V outputdevice, load voltage regulation is 8.3%. Forunregulated devices the load voltage regula-tion is specified over the load range – 10%to 100% of full load.

Line Voltage RegulationThe change in output voltage for a givenchange in input voltage, expressed as per-centages. For example, assume a 12V in-put, 5V output device exhibited a 0.5V chan-ge at the output for a 1.2V change at theinput, line regulation would be 1 %/%.

Output Voltage AccuracyThe proximity of the output voltage to thespecified nominal value. This is given as atolerance envelope for unregulated deviceswith the nominal input voltage applied. Forexample, a 5V specified output device at100% load may exhibit a measured outputvoltage of 4.75V, i.e. a voltage accuracy of–5%).

Input and Output RippleThe amount of voltage drop at the input, oroutput between switching cycles. The valueof voltage ripple is a measure of the storageability of the filter capacitors.

Input to Output IsolationThe dielectric breakdown strength test be-tween input and output circuits. This is theisolation voltage the device is capable ofwithstanding for a specified time, usually 1 se-cond (details please see chapter “IsolationVoltage vs. Rated Working Voltage”).

Insulation ResistanceThe resistance between input and output cir-cuits. This is usually measured at 500V DC.

Efficiency at FulI LoadThe ratio of power delivered from the deviceto power supplied to the device when thepart is operating under 100% load condi-tions.

Temperature DriftThe change in voltage, expressed as a per-centage of the nominal, per degree changein ambient temperature. This parameter isrelated to several other temperature depen-dent parameters, mainly internal componentdrift.

Temperature above AmbientThe temperature rise developed by the devi-ce under full load conditions. This is relatedto efficiency.

Switching FrequencyThe nominal frequency of operation of theswitching circuit inside the DC-DC conver-ter. The ripple observed on the input andoutput pins is usually twice the switchingfrequency, due to full wave rectification andthe push-pull configuration of the driver circuit.

No Load Power ConsumptionThis is a measure of the switching circuitsrequirement to function; it is determinedwith zero output load and is a limiting factorfor the total efficiency of the device.

Isolation CapacitanceThe input to output coupling capacitance.This is not actually a capacitor, but the para-sitic capacitive coupling between the trans-former primary and secondary windings.Isolation capacitance is typically measuredat 1 MHz to reduce the possibility of the on-board filter capacitors affecting the results.

Mean Time Between Failure (MTBF)These figures are calculated expected devi-ce lifetime figures using the hybrid circuitmodel of MIL-HDBK-217F. POWERLINE con-verters also can use BELLCORE TR-NWT-000332 for calculation of MTBF. The hybridmodel has various accelerating factors foroperating environment (πE), maturity πL),screening (πQ), hybrid function (πF) and asummation of each individual componentcharacteristic (λC). The equation for thehybrid model is then given by:

λ = ∑ (NC λC) (1 + 0.2πE) πL πF πQ

(failures in 106 hours)

The MTBF figure is the reciprocal of this value.In the data book all figures for MTBF aregiven for the ground benign (GB) environ-

ment (πE = 0.5); this is considered the mostappropriate for the majority of applicationsin which these devices are likely to be de-signed in. However, this is not the only ope-rating environment these devices can beused for, hence those users wishing toincorporate these devices into a moresevere environment can calculate the pre-dicted MTBF from the following data.The MIL-HDBK-217F has military environ-ments specified, hence some interpretationof these is required to apply them to stan-dard commercial environments. Table 1 givesapproximate cross references from MIL-HDBK-217F descriptions to close commer-cial equivalents. Please note that these arenot implied by MIL-HDBK-217F, but are ourinterpretation. Also we have reduced thenumber of environments from 14 to 6,which are most appropriate to commercialapplications. For a more detailed understan-ding of the environments quoted and thehybrid model, it is recommended that a fullcopy of MIL-HDBK-217F is obtained.

It is interesting to note that space flight andground benign have the same environmentfactors. It could be suggested that the act ofachieving space flight should be the deter-mining environmental factor (i.e. missilelaunch).

The hybrid model equation can therefore berewritten for any given hybrid, at a fixedtemperature, so that the environmental fac-tor is the only variable:

λ = k (1 + 0.2 πE)

The MTBF values for other environment fac-tors can therefore be calculated from theground benign figure quoted at each tempe-rature point in the data book. Hence predic-ted MTBF figures for other environmentscan be calculated very quickly. All the valueswill in general be lower and, since the majo-rity of the mobile environments have thesame factor, a quick divisor can be calcu-lated for each condition. Therefore the onlycalculation necessary is to devide the quo-ted MTBF fig. by the divisor given in table 2.

266 www.recom-international.com


Environment πE πE DivisorSymbol Value

Ground Benign GB 0.5 1.00

Ground Mobile GM 4.0 1.64

Naval Sheltered GNS 4.0 1.64

AircraftInhabited AIC 4.0 1.64Cargo

Space Flight SF 0.5 1.00

Missile Launch ML 12.0 3.09

Table 2: Environmental Factors

Environ- πE MIL-HDBK-271F Commercial Interpretationment Symbol Description or ExamplesGround GB Non-mobile, temperature and Laboratory equipment, testBenign humidity controlled environments instruments, desktop PC's,

readily accessible to maintenance static telecommsGround GM Equipment installed in wheeled or In-vehicle instrumentation,Mobile tracked vehicles and equipment mobile radio and telecomms,

manually transported portable PC'sNaval NS Sheltered or below deck Navigation, radio equipmentSheltered equipment on surface ships or and instrumentation below

submarines deckAircraft AIC Typical conditions in cargo Pressurised cabin compart-Inhabited compartments which can be ments and cock-pit, in flightCargo occupied by aircrew entertainment and non-safety

critical applicationsSpace SF Earth orbital. Vehicle in neither Orbital communications satel-Flight powered flight nor in atmospheric lite, equipment only operated

re-entry once in-situMissile ML Severe conditions relating Severe vibrational shock and Launch to missile launch very high accelerating forces,

sattelite launch conditions

Table 1: Interpretation of Environmental Factors

NoiseInput conducted noise is given in the lineconducted spectra for each DC-DC conver-ter (see EMC issues for further details).Noise is affected significantly by PCB layout,measurement system configuration, termi-nating impedance etc., and is difficult toquote reliably and with any accuracy otherthan via a spectrum analysis type plot.There will be some switching noise presenton top of the ripple, however, most of this iseasily reduced by use of small capacitors orfilter inductors, as shown in the applicationnotes.

Operating temperature range:Operating temperature range of the conver-ter is limited due to specifications of thecomponents used for the internal circuit ofthe converter.

The diagram for temperature deratingshows the safe operating area (SOA) withinthe device is allowed to operate.

Up to a certain temperature 100% powercan be drawn from the device, above thistemperature the output power has to beless to ensure function and guarantee spe-cifications over the whole lifetime of theconverter.

These temperature values are valid fornatural convection only. If the converter isused in a closed case or in a potted PCBboard higher temperatures will be presentin the nearer area around the converterbecause the convection may be blocked.

If the same power is also needed at highertemperatures eighter the next higher watta-ge series should be chosen or if the conver-ter has a metal case using a heatsink maybe considererd.

Calculation of heatsinks:All converters in metal-case can have a heat-sink mounted on so the heat generated bythe converters internal power dissipationPd can be remove. The general specificati-on of the whole thermal system incl. heat-sink is it’s thermal resistance RTH case-ambient

Via this the maximal allowed output powercan be extended at higher ambient tempe-ratures Tambient still meeting the power-deratings prescriptions.

Power dissipation Pd:

Figure 1: Standard Isolated Configurations

0V+VO

-VODC

GND

DC

GND

DC

DC

0V

+VO(VO+VIN)

VCC

0VDC

-VODC

+VO

GND

VCC

VCC

Figure 2: Alternative Supply Configurations

b) Non-lsolated Negative Rail

a) Non-lsolated Dual Rails

c) Dual Isolated Outputs (U/T)

GND DC

DC

0V2

DC

-VODC

0V

+VO

VO

DC

GND

GND

VIN DC

VIN0V

VIN

VO20V1VO1

c) Twin Isolated Outputs (U/T)

b) Dual Output A/B, C/D, G/H/J/K

a) Single Output (N/O, L, M, I etc.)

d PPP −=−= in out PPout

outEfficiency

−=RTHcase-ambient

dP

Tcase Tambient

267www.recom-international.com


IsolationOne of the main features of the majority ofRecom International Power GmbH DC-DCconverters is their high galvanic isolationcapability. This allows several variations oncircuit topography by using a single DC-DCconverter.

The basic input to output isolation can beused to provide either a simple isolated out-put power source, or to generate differentvoltage rails, and/or dual polarity rails (seefigure 1).

These configurations are most often foundin instrumentation, data processing andother noise sensitive circuits, where it isnecessary to isolate the load and noise pre-sented to the local power supply rails, fromthat of the entire system. Usually local sup-ply noise appears as common mode noiseat the converter and does not pollute themain system power supply rails.

The isolated positive output can be con-nected to the input ground rail to generate anegative supply rail if required. Since theoutput is isolated from the input, the choiceof reference for the output side can be rela-tively arbitrary, for example an additionalsingle rail can be generated above the mainsupply rail, or offset by some other DC value(see figure 2).

Regulated converters need more considera-tion than the unregulated types for mixing

the reference level. Essentially the singlesupply rail has a regulator in its +VO railonly, hence referencing the isolated groundwill only work, if all the current return isthrough the DC-DC and not via other exter-nal components (e.g. diode bias, resistorfeed). Having an alternative return path canupset the regulation and the performance ofthe system may not equal that of the con-verter.

Isolation Voltage vs. Rated WorkingVoltageThe isolation voltage given in the datasheetis valid for 1 second flash tested only.If a isolation barrier is required for longer orinfinite time the Rated Working Voltage hasto be the criteria.Conversion of Isolation Voltage to RatedWorking Voltage can be done by using thistable or graph.

Example: RP30-2405SEW starts deratingwithout heatsink at +65°C but the desiredoperation is 30W at +75°C so the size ofthe heatsink has to be calculated.

So it has to be ensured that the thermalresistance between case and ambient is6,1°C/W max.

When mounting a heatsink on a case thereis a thermal resistance RTH case-heatsink be-tween case and heatsink which can bereduced by using thermal conductivity pastebut cannot be eliminated totally.

With this value you can choose a heatsinkfrom it’s suppliers.

If normal convection heatsinks do not meetthis value or the dimensions would get toobig a heatsink with fan may be the solution.But the fan requires also power so the

efficiency of the whole converter applicationwould suffer from this.

In most cases choosing the next higherwattage-series and using power-decreas-ing via derating may be the more efficientsolution.

Efficiency = 88% max.P =out 30 W

Tcase = 100 °C (max. allowed case temperature)Tambient = 75 °C

dP −= =PPout

outEfficiency

30 W

88 %– 30 W = 4,1 W

−=RTHcase-ambient

dP

Tcase Tambient = 100 °C – 75 °C = 6,1°C/W4,1 W

=RTHcase-ambient RTHcase-heat sink + RTHheat sink-ambient

Heatsink mounted on casewithout thermal conductivity paste RTH case-heatsink = ca. 1…2 °C/W

Heatsink mounted on casewith thermal conductivity paste RTH case-heatsink = ca. 0,5…1 °C/W

Heatsink mounted on case with thermal conductivity paste and electrical-isolation-film RTH case-heatsink = ca. 1…1,5 °C/W

If a heatsink will be mounted on the converter without electrical isolation to the (floating)case it’s thermal resistance has to be at least:

= =RTHheat sink-ambient RTHcase-ambient RTHcase-heat sink− 6,1 °C/W – 1°C/W = 5,1 °C/W

0 1 2 3 4 5 6 7

Rated Working Voltage (kV)

Isol

atio

n Te

st V

olta

ge (k

V) 12

10

8

6

4

2

0

Figure 5: IEC950 Test Voltage for Electrical Strength Tests

Table 2: Typical Breakdown Voltage Ratings

Isolation Test Voltage (Vrms) Rated Working Voltage (Vrms)

1000 130

1500 230

3000 1100

6000 3050



ConnectingDC-DC Converters in SeriesGalvanic isolation of the output allows mul-tiple converters to be connected in series,simply by connecting the positive output ofone converter to the negative of another (seefigure 3). In this way non-standard voltagerails can be generated, however, the currentoutput of the highest output voltage conver-ter should not be exceeded.

When converters are connected in series,additional filtering is strongly recommended,as the converters switching circuits are notsynchronised. As well as a summation of theripple voltages, the output could also produ-ce relatively large beat frequencies. A capa-citor across the output will help, as will aseries inductor (see filtering).

ConnectingDC-DC Converters in ParallelIf the available power output from a singleconverter is inadequate for the application,then multiple converters can be paralleled toproduce a higher output power.

It should be noted that it is always prefera-ble to parallel multiple converters of thesame type. For example, if a 2.5W conver-ter is required, then either 2 C/D should beused or 3 A/B, not one C/D and one A/B. Thereason for this is that, the output voltagesare not sufficiently well matched to guaran-tee that a C/D would supply twice as muchas an A/B and the situation could occur,where there was only 1W being drawn from

the C/D and 1.5W from the A/B. Even withparallel converters of the same type, loadingwill be uneven, however, there is only likelyto be around a 10% difference in outputload, when the output voltages are well mat-ched.When connecting converter outputs, itshould be remembered that, the switchingwill not be synchronous, hence some formof coupling should be employed. One possi-ble solution is to use a diode feed, this issuitable mainly for 12V and 15V outputtypes only, where the diode voltage drop(typically 0.6V) will not significantly affectthe circuit functionality (see figure 4). With5V and 9V supplies the diode drop is gene-rally too large to consider it as a suitablemeans of connecting paralleled converters.This method also has a beat frequency thatwill superimpose itself over the ripple of thetwo converters. This can be reduced byusing an external capacitor at the paralleledoutput.

The preferred method of connecting conver-ters in parallel is via series inductors on theoutput (see figure 5). This configuration notonly has a lower loss of voltage than thediode method, but by suitable choice of in-ductor and an additional external capacitor,the beat frequency can be significantly re-duced, as will the ripple from each conver-ter.

Recommended Valuesfor Paralleled DC-DC ConvertersThe capacitance value used (Cout) shouldbe approximately 1µF per parallel channel(i.e. for 2 parallel single output converters,2µF between the common positive outputand OV).

The same comments can be applied to theinput circuit for converters whose inputs areparalleled, and similar values for inductanceand input capacitance should be used asshown above.

In general, paralleling of converters shouldonly be done when essential, and a higherpower single converter is always a prefera-ble solution. There should always be a cor-rection factor of the maximum power ratingto allow for mismatch between converters,and a selection at full load test is recom-mended, to ensure the output voltage ismatched to within 1% or 2%. In general afactor of 0.9 should be used to provide apower safety margin per converter (e.g. 2C/D converters paralleled should only beused up to a power level of 3.6W, not their4W maximum). At most three DC-DC con-verters can be paralleled with a high level ofconfidence in the overall performance. If thecircuit needs more power than three con-verters in parallel, then a single converterwith a much higher power rating should beconsidered.

Regulated output DC-DC converters shouldnot be paralleled, since their output voltagewould need to be very accurately matched,to ensure even loading (to within the tole-rance of the internal linear regulator). Pa-ralleling regulated converters could causeone of the parts to be overloaded. If a highpower regulated supply is required, it wouldbe better to parallel unregulated convertersand add an external linear regulator.

Filtering

All Recom isolated DC-DC converters have afixed characteristic frequency at which thedevice operates. This fixed frequency allowsfiltering that is relatively simple compared topulse-skipping types. In a pulse skippingconverter a large range of frequencies areencountered, as the device adjusts thepulse interval for loading conditions.When reducing the ripple from the conver-ter, at either the input or the output, thereare several aspects to be considered.Recom recommend filtering using simplepassive LC networks at both input and out-

0V

+VO

0V

+VO

DC

VCC

DC

DC

GND

DC

2VO

Figure 3: Connecting DC-DC Converters in Series

0V

+VO

DC

VCC

DC

DC

GND

DC

Figure 4: Diode Coupled Paralleled DC-DC Converters

DC

DC

DC

DC

VCC

GND

0V

+VO

COUT

LOUT

LOUT

LIN

LIN

CIN

Figure 5: Fully Filtered Paralleled DC-DC Converters



put (see figure 6). A passive RC networkcould be used, however, the power lossthrough a resistor is considered too high.The self-resonant frequency of the inductorneeds to be significantly higher than thecharacteristic frequency of the DC-DC (typi-cally 1OOkHz for Recom DC-DC converters).The DC current rating of the inductor alsoneeds consideration, a rating of approximate-ly twice the supply current is recommended.The DC resistance of the inductor is the finalconsideration that will give an indica-tion ofthe DC power loss to be expected from theinductor.The value of inductor and capacitor to use isgiven in the table above for the majority ofRecom DC-DC converters. The capacitanceis chosen to form a pi filter to match theinput or output capacitor of the DC-DC con-verter. The inductor is chosen to causeheavy attenuation of the characteristic fre-quency when combined with the givencapacitors.

Output Filtering calculation:Calculating of the filtering components canbe done using

This frequency should be significant lowerthan the switching frequency of the converter.

Example - RC series:Operating frequency = 85kHz max.

fc =10 % of 85 kHz = 8,5 kHz

However, depending on your application-design and load-situation may interfer withthe calculated filter so testing in the finalapplication and re-adjustment of the com-ponent’s values may be necessary.

When choosing a value for the filteringcapacitor please take care that the maxi-mum capacitive load is within the specifica-tions of the converter.

Limiting Inrush CurrentUsing a series inductor at the input will limitthe current that can be seen at switch on(see figure 7). If we consider the circuit with-out the series inductor, then the input cur-rent is given by;

i = V exp ( – t )R RC

When the component is initially switched on(i.e. t=O) this simplifies to;

i = VR

This would imply that for a 5V input, withsay 50mΩ track and wire resistance, theinrush current could be as large as 1OOA.

This could cause a problem for the DC-DCconverter.A series input inductor therefore not only filtersthe noise from the internal switching circuit,but also limits the inrush current at switch on.

Maximum Output CapacitanceA simple method of reducing the output rip-ple is simply to add a large external capa-citor. This can be a low cost alternative tothe LC filter approach, although not aseffective. There is also the possibility of cau-sing start up problems, if the output capaci-tance is too large.With a large output capacitance at switchon, there is no charge on the capacitors andthe DC-DC converter immediately experien-ces a large current demand at its output.The inrush current can be so large as toexceed the ability of the DC-DC converter,and the device can go into an undefinedmode of operation. In the worst case scena-rio the device can give a lower than expec-ted DC output with a very high ripple. TheDC-DC converter may survive this condition,however, the circuit being supplied is un-likely to function under this supply scheme.

Recom recommend a maximum safe opera-ting value of 10µF for the output per channel.When used in conjunction with a series outputinductor, this value can be raised to 47µF,should extremely low ripple be required.

Settling TimeThe main reason for not fitting a seriesinductor internally is that, many applica-tions require a fast power on time (there isalso a size constraint with our miniatureparts). When the power on voltage is a con-trolled fast ramp, then the output can res-pond within 500µs of the input reaching itstarget voltage (measured on a range of R/Band C/D components under full output loadwithout external filters). The use of externalfilters and additional input or output capaci-tance will slow this reaction time. It is there-fore left to the designer to decide on thepredominant factors affecting their circuit,settling time, or noise performance.

Isolation Capacitanceand Leakage CurrentThe isolation barrier within the DC-DC con-verter has a capacitance, which is a mea-sure of the coupling between input and out-Figure 6: Input and Output Filtering

Figure 7: Input Current & Voltage at Switch On

VIN

time

i =V_R

V_R

Voltage : V = Vin (1 – exp )( )–t__RC

Current : i = exp ( )–t__RC

C0

1

LOUTπ=fc

2

C0

1

LOUTπ=fc

2

C0

1

LOUTπ2=fc 8,5 kHz =

for:

LOUT= 470 Hµ

=

=

=

ππC0

1 1

(2 f )c2LOUT (2 8,5 kHz)2470 uH

745 nF



put circuits. Providing this is the largestcoupling source, a calculation of the leaka-ge current between input and output circuitscan be estimated.Assuming we have a known isolation capa-citance (Cis - refer to DC-DC converter data)and a known frequency for either the noiseor test signal, then the expected leakagecurrent (IL) between input and output circu-its can be calculated from the impedance.The general isolation impedance equationfor a given frequency (f) is given by:

Zf = ___1___j2π Cis

For an R05B05/RB0505D, the isolation ca-pacitance is 18pF, hence the isolation im-pedance to a 50Hz test signal is:

Z50 = ___1_______ = 177 MΩj2π 50 18 pf

I f using a test voltage of 1kVrms,the leakage current is:

iL = Vtest = _1000V_ = 5.65 µAZ

f 177MΩ

It can be easily observed from these simpleequations that the higher the test or noisevoltage, the larger the leakage current, alsothe lower the isolation capacitance, the lowerthe leakage current. Hence for low leakagecurrent, high noise immunity de-signs,high isolation DC-DC converters should beselected with an appropriate low isolationcapacitance.

Overload Protection

Although the use of filtering will preventexcessive current at power-on under normaloperating conditions, there is no protectionagainst an output circuit taking ex-cessivepower, or even going short-circuit. Whenthis happens, the DC-DC converter will takea large input current to try to supply the out-put. Eventually the converter will overheatand destroy itself if this condition is not rec-tified (short circuit overload is only guaran-teed for 1 s on an unregulated part).

There are several ways to prevent overloadat the outputs destroying the DC-DC conver-ter. The simplest being a straight forwardfuse, sufficient tolerance for inrush currentis required to ensure the fuse does not blowon power-on (see figure 8). Another simple

scheme that can be applied is a circuitbreaker.There is also the potential to add some in-telligence to the overload scheme by eitherdetecting the input current, or the outputvoltage (see figure 9). The simplest imple-mentation for overload protection at theinput is to have the device supplied via alinear regulator with an internal thermalshutdown facility. This does however reducethe overall efficiency significantly.If there is an intelligent power managementsystem at the input, using a series resistor(in place of the series inductor) and detec-ting the voltage drop across the device tosignal the management system can beused. A similar scheme can be used at the

output to determine the output voltage,however, if the management system is onthe input side, the signal will need to be iso-lated from the controller to preserve thesystem isolation barrier (see figure 10).The thermal dissipation in a series resistoron the output can also be used to determi-ne overloading and preserve the isolationbarrier. If a thermistor or other thermallysensitive device is mounted close to theresistor, this can be used to indicate an over-load condition. System temperature will alsoneed to be known to provide a suitable off-set for different operating environments.There are several other current limitingtechniques that can be used to detect anoverload situation, the suitability of these is

DC

DC

GND

FuseVIN

Figure 8: Simple Overload Protection

DC

DC

DC

DCVCC

REG

GND

DC

DCVCC

RIN

VOL

GND

GND

VCC ILIMIT

RGND

R1

R2

Figure 9: Input Monitored Overload Protection

a) Linear Regulator with Internal Thermal Shutdown

b) Series Resistor for Input Current Measurement

c) Ground Current Monitor

Choose current limit (ILIMIT)and ground resistor (RGND) sothat : 0.7V = RGND x ILIMIT.



left to the designer. The most importantthing to consider is how this information will beused. If the system needs to signal to a control-ler the location or module causing the overload,some form of intelligence will be needed. Ifthe device simply needs to switch off, a sim-ple fuse type arrangement will be adequate.

All Recom DC-DC converters, which includean internal linear regulator, have a thermaloverload shut-down condition, which pro-tects these devices from excessive over-load. If this condition is to be used to informa power management system, the most sui-table arrangement is the output voltage

detector (see figure 10a), since this will fall to near zero on shut-down. A thermal probeon the case of the DC-DC converter is alsoa possible solution.

Input VoltageDrop-Out (brown-outs)When the input voltage drops, or is mo-mentarily removed, the output circuit wouldsuffer similar voltage drops. For short pe-riod input voltage drops, such as when otherconnected circuits have an instantaneouscurrent demand, or devices are plug-ged inor removed from the supply rail while 'hot', asimple diode-capacitor arrangement canprevent the output circuit from being effec-ted.The circuit uses a diode feed to a largereservoir capacitor (typically 47µF electroly-tic), which provides a short term reservecurrent source for the converter, the diodeblocking other circuits from draining thecapacitor over the supply rail. When combi-ned with an in-line inductor this can also beused to give very good filtering. The diodevolt drop needs to be considered in thepower supply line under normal supply con-ditions. A low drop Schottky diode is recom-mended (see figure 11).

No Load Over Voltage Lock-OutUnregulated DC-DC converters are expectedto be under a minimum of 10% load, hencebelow this load level the output vol-tage isundefined. In certain circuits this could be apotential problem.The easiest way to ensure the output volta-ge remains within a specified tolerance, is toadd external resistors, so that there isalways a 10% loading on the device (seefigure 12). This is rather inefficient in that10% of the power is always being taken bythis load, hence only 90% is available to theadditional circuitry.Zener diodes on the output are another sim-ple method. It is recommended that thesebe used with a series resistor or in-ductor,as when the Zener action occurs, a largecurrent surge may induce signal noise intothe system.

Long Distance Supply LinesWhen the supply is transmitted via a cable,there are several reasons why using an iso-lated DC-DC converter is good design prac-

Figure 10 : Ouput Monitored Overload Protection

DC

DC

VCC

GND

DC

DC

VCC

GND

+VO

OV

RD

VOL

RO Opto-Isolator

VO

OV

RO

VOL

NTC Thermistor

a) Opto-Isolated Overload Detector(On overload +VO falls and the LED switches off, the VOL. line is then pulled high.)

b) Thermal Overload detector

DC

DC47µF

LINZDX60

Output Circuit

Figure 11 : Input Voltage Drop-out



tice (see figure 13). The noise pick up andEMC susceptibility of a cable is high compa-red to a pcb track. By isolating the cable viaa DC-DC converter at either end, any cablepick-up will appear as common mode noiseand should be self-cancelling at the conver-ters.Another reason is to reduce the cable lossby using a high voltage, low current powertransfer through the cable and reconvertingat the terminating circuit. This will also redu-ce noise and EMC susceptibility, since thenoise voltage required to affect the rail, isalso raised.For example, compare a system having a 5Vsupply and requiring a 5V, 500mW output ata remote circuit. Assume the connectingcable has a 100Ω resistance. Using anR05N05/RN0505 to convert the power ateither end of the cable, with a 100mA cur-rent, the cable will lose 1W (I2R) of power.The RO/RN would not be suitable, since this

is its total power delivery; hence there is nopower available for the terminating circuit.Using a RO5B12/RB0512D to generate 24Vand a R24A05/RA2405D to regenerate 5V,only a 21 mA supply is required through thecable, a cable loss of 44mW.

LCD Display BiasA LCD display typically requires a positive ornegative 24V supply to bias the crystal. TheR05024/RO-0524S (custom) converter wasdesigned specifically for this application.Having an isolated OV output, this de-vicecan be configured as a +24V supply byconnecting this to the GND input, or a –24Vsupply by connecting the +Vo output to GND(see figure 14).

EIA-232 InterfaceIn a mains powered PC often several sup-ply rails are available to power a RS232interface. However, battery operated PC’s or

remote equipment having a RS232 inter-face added later, or as an option, may nothave the supply rails to power a RS232interface. Using a RB0512S/R05B12 is asimple single chip solution, allowing a fullyEIA-232 compatible interface to be im-plemented from a single 5V supply rail,and only 2 additional components (see fi-gure 15).

3V/5V Logic Mixed Supply RailsThere has been a lot of attention given tonew l.C.'s and logic functions operating atwhat is rapidly emerging as the standardsupply level for notebook and palmtop com-puters. The 3.3V supply is also gaining rapidacceptance as the defacto standard for per-sonal telecommunications, however, not allcircuit functions required are currently avai-lable in a 3.3V powered IC. The system desi-gner therefore has previously had only twooptions available; use standard 5V logic orwait until the required parts are available ina 3V form, neither being entirely satisfac-tory and the latter possibly resulting in lostmarket share.There is now another option, mixed logicfunctions running from separate supplyrails. A single 3.3V line can be combinedwith a range of DC-DC converters fromRecom, to generate voltage levels to run vir-tually any standard logic or interface IC.The Recom range includes dual output partsfor powering analogue bipolar and amplifierfunctions (A/B series), as well a single out-put function for localised logic functions(L/M, N/O series). A typical example mightbe a RS232 interface circuit in a laptop PCusing a 3.3V interface chip (such as theLT1330), which accepts 3.3V logic signalsbut requires a 5V supply (see figure 16).Recom has another variation on this themeand has developed two 5V to 3.3V stepdown DC-DC converters (R05L03/RL-0503and R05O03/R0-0503). These have beendesigned to allow existing systems tostart incorporating available 3.3V l.C.'swithout having to redesign their powersupply.This is particularly important when trying toreduce the overall power demand of asystem, but not having available all of thefunctions at the 3.3V supply.The main application for this range of de-vices are system designers, who want to

R2

DC

DC

R10%

DC

DC

R10%

Figure 12: No Load over Voltage Lock-Out

Figure 13: Long Distance Power Transfer

VINTarget Circuit

DC

DC

DC

DCGND

R05B12 R24O05Cable



provide some functionality that requires ahigher voltage than is available from thesupply rail, or for a single localised function.Using a fully isolated supply is particularlyuseful in interface functions and systemsmaintaining separate analogue and digitalground lines.

Isolated DataAcquisition SystemAny active system requiring isolation willneed a DC-DC converter to provide thepower transfer for the isolated circuit. In adata acquisition circuit there is also the needfor low noise on the supply line; hence goodfiltering is required.The circuit shown (see figure 17) provides avery high isolation barrier by using anG/H/J/K converter; to provide the power iso-lation and SFH610 opto-isolators for thedata isolation. An overall system isolation of2.5kV is achieved.

EMC Considerations

When used for isolating a local power supp-ly and incorporating the appropriate filtercircuits as illustrated in Fig. 17), DC-DC con-verters can present simple elegant solutionsto many EMC power supply problems. Therange of fixed frequency DC-DC convertersis particularly suitable for use in EMC pro-blem situations, as the stable fixed switchingfrequency gives easily characterised andeasily filtered output.The following notes give suggestions toavoid common EMC problems in power sup-ply circuits. A more extensive discussion onother aspects of EMC is available in theRecom EMC Design Guidelines book.

–24VDC

DC

(up to 42mA)

RO5024 & RO-0524S

LiquidCrystalDisplay

Figure 14: LCD Display Bias

Figure 15: Optimised RS232 Interface

+12V

SN75C185

RO5B12 & RB-0512D

EIA-232 Port

DB9S

Con

nect

or

–––DCD–––DSR––RX

––TX–––CTS–––DTR––RI

VCC

GND

VDD5V

0V

–V0 DC

DC+V0

–––RTS



3.3V220nF

3

4 27

14

17

5

26

1 2 28

+ +

___TX125

___RX1

___RX1

___TX1

200nF

+V –V

RS2323.3V Logic

1µF 100nF

7DC

DC

RL0305R03L05

83

1 OV

+5V

3.3VCC

GND

VCC

24 6

GNDLT1330

GND

Figure 16: RS232 Interface with 3V Logic

Figure 17: Isolated Serial ADC System

__CS

Data

CS

Status

CLK

5V

5V

1K2

1K2

4K7

4K7

5V L

ogic

Circ

uit

Opto Isolators

+5V

4K7

+5V

4K7

ZN509Status

1K2

CLK GND

Vref

VCC

+5V

470νFAIN

Data

DC

DC

5V

1µF

+5V47µH

RH0505 & R05H05

1K2

1K2

SFH610



Power Supply Considerations Eliminate loops in supply lines (see

figure 18).

Decouple supply lines at local bounda-ries (use RCL fitters with low Q, see figure 19).

Place high speed sections close to the power line input, slowest section furthest away (reduces power plane transients, see figure 20).

Isolate individual systems where pos-sible (especially analogue and digital systems) on both power supply and sig-nal lines (see figure 21).

An isolated DC-DC converter can provide asignificant benefit to reducing susceptibilityand conducted emission, due to isolatingboth power rail and ground from the sys-tem supply. The range of DC-DC convertersavailable from Recom all utilise toroidalpower transformers and as such have neg-ligible EMI radiation (they also incorporatethe recommended pcb layout suggestionsas stated in Recom EMC Guidelines Databook).Isolated DC-DC converters are switchingdevices and as such have a characteristicswitching frequency, which may need someadditional filtering. Some commercial con-verters offer a pulse-skipping technique,which although offering a flat efficiency res-ponse, gives a very wide spectral range ofnoise, since it does not have a fixed charac-teristic frequency. Recom devices feature afixed frequency converter stage, which isstable across its full loading and temperatu-re curve, hence it is very easy to filter theswitching noise using a single series induc-tor.

Interpretation ofDC-DC Converter EMC DataElectromagnetic compatibility (EMC) of elec-trical and electronic products is a measureof electrical pollution. Throughout the worldthere are increasing statutory and regulatoryrequirements to demonstrate the EMC ofend products. In Europe the EC directive89/336/EEC requires that, any product soldafter 1 January 1996 complies with a seriesof EMC limits, otherwise the product will beprohibited from sale within the EEC and theseller could be prosecuted and fined.Although DC-DC converters are generallyexempt from EMC regulations on the groundsthat these are component items, it is thebelief of Recom that the information on theEMC of these components can help de-signers ensure their end product can meetthe relevant statutory EMC requirements. Itmust be remembered however, that the DC-DC converter is unlikely to be the last com-ponent in the chain to the mains supply,hence the information quoted needs inter-pretation by the circuit designer to deter-mine its impact on the final EMC of theirsystem.

CCT1 CCT2

GND

VCC

PSU

CCT1 CCT2

GND

VCC

PSU

CCT1 CCT2

GND

VCC

Figure 18: Eliminate Loops in Supply Line

Figure 19: Decouple Supply Lines at Local Boundaries



The notes given here are aimed at helpingthe designer interpret the effect the DC-DCconverter will have on the EMC of their endproduct, by describing the methods andrationale for the measurements made.Where possible CISPR and EN standardshave been used to determine the noisespectra of the components, however, all ofthe standards reference mains poweredequipment and interpretation of these spe-cifications is necessary to examine DC sup-plied devices.

Conducted andRadiated EmissionsThere are basically two types of emissionscovered by the EC directive on EMC, radi-ated and conducted. Conducted emissionsare those transmitted over wire connectingcircuits together and covers the frequencyspectrum 150kHz to 30MHz. Radiated arethose emissions transmitted via electromag-netic waves in air and cover the frequencyspectrum 30MHz to 1GHz. Hence the ECdirective covers the frequency spectrum

150kHz to 1GHz, but as two separate anddistinct modes of transmission.The Recom range of DC-DC converters fea-tures toroidal transformers within the com-ponent. These have been tested and provedto have negligible radiated noise. The lowradiated noise is primarily due to toroidalshaped transformers maintaining the mag-netic flux within the core, hence no magneticflux is radiated by design. Due to the excep-tionally low value of radiated emis-sion, onlyconducted emissions are quoted.Conducted emissions are measured on theinput DC supply line. Unfortunately no stan-dards exist for DC supplies, as most stan-dards cover mains connected equipment.This poses two problems for a DC supplieddevice, firstly no standard limit lines can bedirectly applied, since the DC supplied devi-ce does not directly connect to the mains,also all reference material uses the earth-ground plane as reference point. In a DCsystem often the OV is the reference, how-ever, for EMC purposes, it is probably moreeffective to maintain the earth as the refe-rence, since this is likely to be the refe-rencethat the shielding or casing is con-nected to.Consequently all measurements quoted arereferenced to the mains borne earth.

Line ImpedanceStabilisation Network (LISN)It is necessary to ensure that any measure-ment of noise is from the device under test(DUT) and not from the supply to this devi-ce. In mains connected circuits this is im-portant and the mains has to be filtered priorto supply to the DUT. The same ap-proachhas been used in the testing of DC-DC con-verters and the DC supply to the converterwas filtered, to ensure that no noise fromthe PSU as present at the measuring instru-ment.A line impedance stabilisation network(LISN) conforming to CISPR 16 specifica-tion is connected to both positive and ne-gative supply rails and referenced to mainsearth (see figure 22). The measurementsare all taken from the positive supply rail,with the negative rail measurement pointterminated with 50W to impedance matchthe measurement channels.

Power Input

Filter

PSU

High SpeedCircuit

Medium SpeedCircuit

Low SpeedCircuit

DC Circuit

Local

Figure 20: Place High Spead Circuit Close to PSU

CCT1

GND

VCC

DCDC CCT2

DCDC

Figure 21 : Isolate Individual Systems

–

+

LISN

LISN

DCDC

To Spectrum Analyser

Power Supply50Ω

Termination

Load

Figure 22: Filtered Supply to DC-DC Converter



ShieldingAt all times the DUT, LlSN's and all cablesconnecting any measurement equipment,loads and supply lines are shielded. Theshielding is to prevent possible pick-up oncables and DUT from external EMC sources(e.g. other equipment close by). The shiel-ding is referenced to mains earth (see figu-re 22).

Line Spectra of DC-DC ConvertersAll DC-DC converters are switching devices,hence, will have a frequency spectra. Fixedinput DC-DC converters have fixed swit-ching frequency, for example the C/D rangeof converters has a typical switching fre-quency of 75kHz. This gives a stable andpredictable noise spectrum regardless ofload conditions.

If we examine the noise spectrum closely(see figure 23) we can see several distinct

peaks, these arise from the fundamentalswitching frequency and its harmonics (oddlabelled line spectra) and the full rectifiedspectra, at twice the fundamental switchingfrequency (even labelled line spectra).Quasi-resonant converters, such as theRecom range, have square wave switchingwaveforms, this produces lower ripple and ahigher efficiency than soft switching devi-ces, but has the drawback of having a rela-tively large spectrum of harmonics.

The EC regulations for conducted interfer-ence covers the bandwidth 150kHz to30MHz. Considering a converter with a100kHz nominal switching frequency, thiswould exhibit 299 individual line spectra.There will also be a variation of absoluteswitching frequency with production varia-tion, hence a part with a 90kHz nominal fre-quency would have an additional 33 linesover the entire 30MHz bandwidth. Absoluteinput voltage also produces slight variationof switching frequency (see figure 24). Hence,to give a general level of conducted noise,we have used a 100kHz resolution band-width (RBW) to examine the spectra in thedata sheets. This wide RBW gives a maxi-mum level over all the peaks, rather than theindividual line spectra. This is easier to readas well as automatically compensating forvariances in switching frequency due to pro-duction variation or differences in absoluteinput voltage (see figure 25).The conducted emissions are measuredunder full load conditions in all cases. Underlower loads the emission levels do fall,hence full load is the worst case conditionfor conducted line noise.

Temperature Performanceof DC-DC ConvertersThe temperature performance of the DC-DCconverters detailed in this book is alwaysbetter than the quoted operating tempera-ture range. The main reason for being con-servative on the operating temperaturerange is the difficulty of accurately specify-ing parametric performance outside thistemperature range.There are some limiting factors which provi-de physical barriers to performance, such asthe Curie temperature of the core ma-terialused in the DC-DC converter (the lowestCurie temperature material in use at Recomis 125°C). Ceramic capacitors are usedalmost exclusively in the DC-DC converters

Figure 23: Individual Line Spectra

50

40

30

20

10

0Freq

uenc

y (k

Hz)

0 2 4 6 8 10

Input Voltage (V)

12 14

Figure 24: Frequency Voltage Dependency

Figure 25 : V Spectrum

0

1

2

3

4

5

6

7

8

9

10

11

12

13

100

Frequency (kHz)

100

80

60

40

20

0

Frequency

Cond

ucte

d Em

issi

on (d

BuV)

100

80

60

40

20

100kHz 1MHz 10MHz 100MHz

0Cond

ucte

d Em

issi

on (d

BuV)

200 300 400 500



because of their high reliability and exten-ded life properties, however, the absolutecapacity of these can fall when the tempe-rature rises above 85°C (ripple will increa-se). Other considerations are the power dis-sipation within the active switching compo-nents, although these have a very high tem-perature rating. Their current carrying capa-city derates, as temperature exceeds100°C.Therefore this allows the DC-DC convertersto be used above their specified operatingtemperature, providing the derating of powerdelivery given in the specification is adheredto. Components operating outside the quotedoperating temperature range cannot be ex-pected to exhibit the same parametric per-formance that is quoted in the specification.An indication of the stability of a device canbe obtained from the change in its operatingfrequency, as the temperature is varied (seefigure 26). A typical value for the frequencyvariation with temperature is 0.5% per °C, avery low value compared to other commer-cial parts. This illustrates the ease of filteringof Recom DC-DC converters, since the fre-quency is so stable across load and tempe-rature ranges.

Transfer MouldedSurface Mount DC-DC Converters

Production Guideline Application Note

The recent introduction by Recom of a newand innovative method of encapsulatinghybrid DC-DC converters in a transfer moul-ded (TM) thermoset epoxy plastic has enab-led a new range of surface mount (SM) DC-DC converters to be brought to market,which addresses the component placementwith SOIC style handling.

With any new component there are of coursenew lessons to be learned with the moun-ting technology. With the new SS/SD rangeof DC-DC converters, the lessons are notnew as such, but may require different pro-duction techniques in certain applications.

Component MaterialsThe body of the TM product range is a highthermally conductive thermoset epoxy pla-stic.The advantage of thermoset materialsin this application is that the body does notdeform under post-cure heat cycles (i.e.under high temperature reflow conditions).Consequently there are no precautions re-quired to protect the body during reflow.Other manufacturers components usingthermoplastics may deform, or require aheat shield during the reflow process.The lead frame is a copper material, hencehas a high conductivity and reduces theinternal resistance of tracking within theDC-DC converters. Hybrid designs whichuse film deposition for tracking (or printedinks), feature higher losses within the DC-DC converter, due to their higher resistance.The leads are tinned with a 60:40 lead-tin(Pb:Sn) solder finish. This is a standard leadfinish and compatible with virtually all soldermixes used in a production environment.

Component PlacementThe SS/SD ranges are designed to be hand-led by placement machines in a similar wayto standard SOIC packages. The parts areavailable either in tubes (sticks) or in reels.The parts can therefore be placed usingmachines with either vibrational shuttle,gravity feeders, or reeled feeders.The vacuum nozzle for picking and placingthe components can be the same as used

for a standard 14 pin or 18 pin SOIC (typi-cally a 5mm diameter nozzle). An increase invacuum pressure may be beneficial, due tothe heavier weight of the hybrid com-paredto a standard SOIC part (a typical 14 pinSOIC weighs 0.1g, the SS/SD DC-DC con-verter weighs 1.3g). It is advisable to consultyour machine supplier on choice of vacuumnozzle, if in doubt.If placing these components by hand, twee-ze on the central body area where there areno component pins. Tweezing on the pinscan cause bending and the pin co-planaritycould be compromised.

Component AlignmentThe components can be aligned by eitheroptical recognition or tweezing. If usingtweezer alignment it should be ensured thatthe tweezers are aligning on the componentbody and not on the pins. The componentsthemselves are symmetrical in the body,hence relatively easy to align using eithermethod.

Solder Pad DesignThe SS/SD range of DC-DC converters aredesigned on a pin pitch of 1.27mm (0.05")with 1mm pad widths and 1.75mm padlengths. This allows pads from one part tobe used within a PCB CAD package for for-ming the pad layouts for other SS/SD parts.These pads are wider than many standardSOIC pad sizes (0.64mm) and CAD packa-ges may not accommodate these pins witha standard SOIC pad pattern. It should beremembered that these components arepower supply devices and as such needwider pads and thicker component leads tominimise resistive losses within the inter-connects.Pad patterns for each component are in-clu-ded in the relevant chapter. These should befollowed where appropriate.One of the benefits of the SS/SD approachis that PCB layout can be produced for dualcomponent usage. For example the SD dualoutput DC-DC converter pad layout canaccommodate the SS product to give asingle positive output voltage only, withoutany PCB tracking changes.

Solder Reflow ProfileRECOM's SMD components are designed towithstand a maximum reflow temperature of230°C (for 10 seconds) in in accordance

160

140

120

100

80

60Switc

hing

Fre

quen

cy (k

Hz)

–20 0 20 40 60 80 100

Temperature (°C)

O/N

A/B

C/D

Under Full Load Conditions

Figure 26: Typical Switching Frequency vs. Temperature



with CECC 00802. If multiple reflow profilesare to be used (i.e. the part is to passthrough several reflow ovens), it is recom-mended that lower ramp rates be used thanthe maximum specified in CECC 00802.Continual thermal cycling to this profilecould cause material fatigue, if more than 5maximum ramp cycles are used.In general these parts will exceed the re-flow capability of most IC and passive com-ponents on a PCB and should prove themost thermally insensitive component to thereflow conditions.

Recommended Solder Reflow Profile:

The following 2 graphes shows the typicalrecommended solder reflow profiles forSMD and through-hole cases.

The exact values of the profile’s peak andit’s max. allowed duration is also given in thedatasheet of each converter.For lead-free soldering (we offer our pro-ducts lead-free-approved starting from01/2005) this is still in development soplease ask at our customer service fordetails until there is a general update onthis.

Adhesive Requirements

If SM components are going to be wave sol-dered (i.e. in a mixed through hole and SMPCB) or are to be mounted on both sides ofa PCB, then it is necessary to use an adhe-sive, to fix them to the board prior to reflow.The adhesive prevents the SM parts being'washed off' in a wave solder, and being'vibrated off' due to handling on a doublesided SM board.As mentioned previously, the Recom rangeof SM DC-DC converters are heavier thanstandard SOIC devices. The heavier weightis a due to the size (volume) and internalhybrid construction. Consequently the partsplace a larger than usual stress on their sol-der joints and leads, if these are the onlymethod of attachment. Using an adhesivebetween component body and PCB canreduce this stress considerably. If the finalsystem is to be subjected to shock and vibra-tion testing, then using adhesive attachmentis essential to ensure the parts pass theseenvironmental tests.The SS/SD range of DC-DC converters fromRecom all have a stand-off beneath thecomponent for the application of adhesive tobe placed, without interfering with the sit-ing of the component. Method of adhe-sivedispensing and curing, plus requirementsfor environmental test and in-service repla-cement will determine suitability of adhesi-ves rather than the component itself.However, having a thermoset plastic body,thermoset epoxy adhesive bonding betweenboard and component is the recommendedadhesive chemistry.If the reflow stage is also to be used as acure for a heat cure adhesive, then the com-ponent is likely to undergo high horizontalacceleration and deceleration during thepick and place operation. The adhesive mustbe sufficiently strong in its uncured (green)state, in order to keep the component accu-rately placed.

Adhesive PlacementThe parts are fully compatible with the 3main methods of adhesive dispensing; pintransfer, printing and dispensing. Themethod of placing adhesive will depend onthe available processes in the productionline and the reason for using adhesiveattachment. For example, if the part is on amixed though-hole and SM board, adhesivewill have to be placed and cured prior to

Recommended solder profile – reflow (SMD Type)

Notes: 1. The reflow solder profile is measure on pin connection temperature.

2. Any reflow process need keep the reflow parts internal temperature less than-about 215 °C

Recommended solder profile – wave solder (Through hole parts)

Notes: 1. The wave solder profile is measure on lead temperature.

2. Need keep the solder parts internal temperature less than-about 183 °C



reflow. If using a SM only board and heatcure adhesive, the reflow may be used asthe cure stage. If requiring adhesive forshock and vibration, but using a conformalcoat, then it may be possible to avoid aseparate adhesive alltogether, and the coa-ting provides the mechanical restraint onthe component body.Patterns for dispensing or printing adhe-siveare given for automatic lines. If dis-pensingmanually after placement the patterns forUV cure are easily repeated using a manualsyringe (even if using heat cure adhesive). Ifdispensing manually, dot height and size arenot as important, and the ad-hesive shouldbe applied after the components have beenreflowed. When dispensing after reflow, achip underfill formulation adhesive would bethe preferred choice.These types 'wick' underthe component body and offer a good allround adhesion from a single dispensed dot.The patterns shown allow for the processspread of the stand-off on the component,but do not account for the thickness of thePCB tracks. If thick PCB tracks are to beused, a grounded copper strip should be laidbeneath the centre of the component (careshould be exercised to maintain isolationbarrier limits). The adhesive should notretard the pins reaching their solder padsduring placement of the part, hence low vis-cosity adhesive is recommended.The height of the adhesive dot, its viscosityand slumping properties are critical. The dotmust be high enough to bridge the gap be-

tween board surface and component, butlow enough not to slump and spread, or besqueezed by the component, and so conta-minate the solder pads.If wishing to use a greater number of dots ofsmaller diameter (common for pin transfermethods), the dot pattern can be changed,by following a few simple guidelines. As thenumber of dots is doubled their diametershould be halved and centres should be atleast twice the printed diameter from eachother, but the dot height should re-main at0.4mm. The printed dot should always bepositioned by at least its diameter from thenearest edge of the body to the edge of thedot. The number of dots is not important,provided good contact between adhesiveand body can be guaranteed, but a mini-mum of 2 is recommended.

CleaningThe thermoset plastic encapsulating ma-terial used for the Recom range of surfacemount DC-DC converters is not fully herme-tically sealed. As with all plastic encapsu-lated active devices, strongly reactiveagents in hostile environments can attackthe material and the internal parts, hencecleaning is recommended in inert solutions(e.g. alcohol or water based solvents) and atroom temperature in an inert atmospheres(e.g. air or nitrogen).A batch or linear aqueous cleaning processwould be the preferred method of cleaningusing a deionised water solution.

Custom DC-DC ConvertersIn addition to the standard ranges shown inthis data book, Recom have the capability toproduce custom DC-DC converters designed toyour specific requirements. In general, the partscan be rapidly designed using computer bas-ed CAD tools to meet any input or outputvoltage requirements within the ranges ofRecom standard products (i.e. up to 48V ateither input or output). Prototype samplescan also be produced in short timescales.Custom parts can be designed to your spe-cification, or where the part fits within astandard series, the generic series specifi-cation can be used. All custom parts re-ceive the same stringent testing, inspectionand quality procedures, as standard pro-ducts. Recom custom parts are used inmany applications, which are very specificto the individual customer, however, sometypical examples are:

ECL Logic driver

Multiple cell battery configurations

Telecommunications line equipment

Marine apparatus

Automotive electronics

LCD display power circuitry

Board level instrumentation systems

To discuss your custom DC-DC converterrequirements, please contact Recom techni-cal support desk or your local distributor.



Notes

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Powerline – DC/DC-ConverterPowerline – DC/DC-Converter

5

6

7

8

4

3

21

45.7250.80

Side View18.00

Bottom View19.0012.70

1.88

1.885.08

5.08

2.54

5.08

5.08

5.08

5.60.8

15.20

20.30

23

2322

161514

91011

Bottom View 31.802.5

17.80

4.6 3.8

10.200.25 x 0.50

Rectangular Pin

Pin Pitch Tolerance ±0.35 mm

A I Case: 31.8 x 20.3 x 10.2 mm C2 Case: 33.02 x 33.02 x 17.8 mm



Package Style and Pinning (mm)

18.00

35.00

12.40

2.54

6

39.90

45.00

54321

6789

1011121314

7.30

20.30Bottom View

2.542.54

5.6

Side View

7 8 951 62 3 4

16 17 1814

68.60

10.00 15.40

50.80

56.10

25.405.00

BottomView

dia.1.0

4.0 min.

20.00

10.00

10 1511 12 13

Q I Case: 68.6 x 50.8 x 20 mm

LI Case: 45 x 35 x 18 mmPI Case: 50.8 x 19 x 18 mm


19.94

5.08

33.02

7 6 5 4

1 2 3

14.86

33.0224.00

5.6 min.

17.80

0.8dia.


ISDN Application


Powerline – Definitions and TestingPowerline – Definitions and Testing

The need for EMCMost power converter tests are carriedout with the general test set-up shownin Figure 1. Some general conditionswhich apply (except where noted) totest methods are outlined in these notes:

Adequate DC power source, and normal DC input voltage

+25°C ambient temperature

Full rated output load

47µF100V

C2

47µF100VC1

+Vin

–Vin

DC/DCConverterZ

9L-TF002

L1

L1 = 1102.5 µH Ø 0.5mmDCR = 0.1ΩC1, C2 = 47µF 100V

Aluminum Electrolytic CapacitorRipple: 180mA at 105°C, 120Hz

47µF100V

C2

47µF100VC1

+Vin

–Vin

DC/DCConverterZ

9L-TF009

L1

L1 = 497 µH Ø 0.3mmDCR = 55.1mΩC1, C2 = 47µF 100V

Aluminum Electrolytic CapacitorRipple: 180mA at 105°C, 120Hz

Figure 1-1: EMC application test for: RP10-, RP12-, RP15-, RP20-, RP30-, RP40- and RP60-Serie

Figure 1-2: EMC application test for: RP03-A Serie, RP05-A Serie and RP08-A Serie,

General Test Set-Up

A

V V

A+V

-V

DC/DCConverterunder Test

Adjustable loadDC PowerSource

(VDC or VRMS)

Note: If the converter is under test withremote sense pins, connect these pins

to their respective output pins. All testsare made in "Local sensing" mode.

Figure 1-3: General DC/DC converter test set-up

The following pages offer a rough explanation of basic specifications or details which are unique to the POWERLINE and cannotbefound in the application notes for our other product-series.


Make and record the following measure-ments with rated output load at +25°C:

Output voltage at nominal line (input) voltage. Vout N

Output voltage at high line (input) voltage. Vout H

Output voltage at low line (input)voltage. Vout L

The line regulation is Vout M (the maxi-mum of the two deviations of output)for the value at nominal input in per-centage.

Vout M – Vout N

Vout NX100

Line Regulations

The minimum and maximum input vol-tage limits within which a converter

will operate to specifications.

An input filter, consisting of two capa-citors, is connected in paralell with aseries inductor to reduce input reflec-ted ripple current.

Input Voltage Range

PI Filter

Output Voltage Accuracy

L

C2Output

C1Input

Figure 2: Pπ Filter

With nominal input voltage and ratedoutput load from the test set-up, theDC output voltage is measured with anaccurate, calibrated DC voltmeter.Output voltage accuracy is the diffe-rence between the measured outputvoltage and specified nominal value asa percentage. Output accuracy (as a%)is then derived by the formula:

Vnom ist the nominal, output specified in the conver-ter data sheet.

Vout – Vnom

Vnom NX100

For a multiple output power converter,the percentage difference in the volta-

ge level of two outputs with oppositepolarrities and equal nominal values.

Voltage Balance




Make and record the following measure-ments with rated output load at +25°C:

Output voltage with rated load connected to the output. (Vout FL)

Output voltage with no load or the minimum specified load for theDC-DC converter. (Vout ML)

Load regulation is the difference bet-ween the two measured output volta-ges as a percentage of output voltageat rated load.

The rate at which the DC voltage isswitched in a DC-DC converter or switching power supply.

Because of the high frequency contentof the ripple, special measurementtechniques must be employed so thatcorrect measurements are obtained. A20MHz bandwidth oscilloscope is used,so that all significant harmonics of theripple spike are included.

This noise pickup is eliminated as shown

in Figure 3, by using a scope probewith an external connection ground orring and pressing this directly againstthe output common terminal of thepower converter, while the tip contactsthe voltage output terminal. This provi-des the shortest possible connectionacross the output terminals.

The ratio of output load power con-sumption to input power consumptionexpressed as a percentage. Normally

measured at full rated output powerand nominal line conditions.

Ground Ring

to Scope+Output

-

Vout ML – Vout FL

Vout FLX100

Figure 3:

Load Regulation

Efficiency

Switching Frequency

Output Ripple and Noise



Figure 4 shows a complex ripple voltagewaveform that may be present on theoutput of a switching power supply.There are three components in thewaveform, first is a 120Hz componentthat originates at the input rectifier andfilter, then there is the component atthe switching frequency of the powersupply, and finally there are small highfrequency spikes imposed on the highfrequency ripple.

Peak-PeakAmplitude

Time

Figure 4: Amplitude

Output Ripple and Noise (continued)

Transient Recovery Time

Current Limiting

Fold Back Current Limiting

The time required for the power supplyoutput voltage to return to within a spe-cified percentage of rated value, follow-ing a step change in load current.

Load

Undershoot

OvershootTransientRecovery Time

V out

I out

Time

Input current drawn by a power supplywith the output short circuited.

A method of protecting a power supplyfrom damage in an overload condition,reducing the output current as the loadapproaches short circuit.

Figure: 5 Transient Recovery Time

Rated Io

V out

I out

Figure 6: Fold Back Current LimitingTime



The electrical separation between theinput and output of a converter, (consis-ting of resistive and capacitive isola-

tion) normally determined by transfor-mer characteristics and circuit spacing.

The maximum DC voltage, which maybe applied between the input and out-put terminal of a power supply withoutcausing damage. Typical break-downvoltage for DC-DC converters is500VDC minimum.

With the power converter in a tempera-ture test chamber with rated outputload, make the following measurements:

Output voltage at +25°C ambient temperature.

Set the chamber for maximum operating ambient temperature and allow the power converter to stabilize for 15 to 30 minutes.Measure the output voltage.

Set the chamber to minimum operating ambient temperature and

allow the power converter to stabi-lize for 15 to 30 minutes.

Divide each percentage voltage deviation from the +25°C ambient value by the corresponding tempe-rature change from +25°C ambient.

The temperature coefficient is the hig-her one of the two values calculatedabove, expressed as percent per chan-ge centigrade.

OutputRectifier

andRegulator

Input

Breakdown Voltage

Resistive andCapacitive Isolation

C

R

Isolation

Break-Down Voltage

Temperature Coefficient

Ambient Temperature

Operating Temperature Range

Storage Temperature Range

Figure 7:

The temperature of the still-air im-mediately surrouding an operatingpower supply.

The range of ambient or case tem-perature within a power supply at

which it operates safely and meetsits specifications.

The range of ambient temperatureswithin a power supply at non-ope-

rating condition, with no degrada-tion in its subsequent operation.



Some converters from our Powerlineoffer the feature of trimming the outputvoltage in a certain range around thenominal value by using external trimresistors.Because different series use differentcircuits for trimming no general equati-on can be given for calculating the

trim-resistors. Following trim-tablesgive values for chosing these trim-resistors. If voltages between the giventrim-points are required a linear appro-ximation of the next points is possibleor using trimmable resitors may beconsidered.

Output Voltage Trimming:

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 1,818 1,836 1,854 1,872 1,89 1,908 1,926 1,944 1,962 1,98 Volts

RU = 11,88 5,26 3,09 2,00 1,35 0,92 0,61 0,38 0,20 0,06 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 1,782 1,764 1,746 1,728 1,71 1,692 1,674 1,656 1,638 1,62 Volts

RD = 14,38 6,50 3,84 2,51 1,71 1,17 0,79 0,50 0,27 0,10 KOhms

RP20-, RP30- XX18S

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 2,525 2,55 2,575 2,6 2,625 2,65 2,675 2,7 2,725 2,75 Volts

RU = 36,65 16,57 9,83 6,45 4,42 3,06 2,09 1,37 0,80 0,35 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 2,475 2,45 2,425 2,4 2,375 2,35 2,325 2,3 2,275 2,25 Volts

RD = 50,20 22,62 13,49 8,94 6,21 4,39 3,09 2,12 1,36 0,76 KOhms

RP20-, RP30- XX25S

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 3,333 3,366 3,399 3,432 3,465 3,498 3,531 3,564 3,597 3,63 Volts

RU = 57,96 26,17 15,58 10,28 7,11 4,99 3,48 2,34 1,46 0,75 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 3,267 3,234 3,201 3,168 3,135 3,102 3,069 3,036 3,003 2,97 Volts

RD = 69,43 31,23 18,49 12,12 8,29 5,74 3,92 2,56 1,50 0,65 KOhms

RP15-, RP20-, RP30-, RP40- xx33SRP40-, RP60- xx3305T (Trim for +3.3V)

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 5,05 5,1 5,15 5,2 5,25 5,3 5,35 5,4 5,45 5,5 Volts

RU = 43,22 18,13 10,60 6,97 4,83 3,42 2,43 1,68 1,11 0,65 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 4,95 4,9 4,85 4,8 4,75 4,7 4,65 4,6 4,55 4,5 Volts

RD = 39,42 19,00 11,58 7,74 5,40 3,82 2,68 1,82 1,15 0,61 KOhms

RP15-, RP20-, RP30-, RP40-, RP60- xx05SRP60-xx05D (Trim for +5V)



Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 10,1 10,2 10,3 10,4 10,5 10,6 10,7 10,8 10,9 11 Volts

RU = 90,50 40,65 24,06 15,76 10,79 7,47 5,10 3,33 1,95 0,84 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 9,9 9,8 9,7 9,6 9,5 9,4 9,3 9,2 9,1 9 Volts

RD = 109,06 48,94 28,87 18,83 12,81 8,79 5,92 3,77 2,10 0,76 KOhms

RP15-, RP20- xx05D

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 12,12 12,24 12,36 12,48 12,6 12,72 12,84 12,96 13,08 13,2 Volts

RU = 1019,45 257,41 134,39 84,06 56,68 39,47 27,65 19,03 12,47 7,30 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 11,88 11,76 11,64 11,52 11,4 11,28 11,16 11,04 10,92 10,8 Volts

RD = 270,20 149,63 95,76 65,24 45,59 31,88 21,77 14,01 7,86 2,87 KOhms

RP15-, RP20-, RP30-, RP40-, RP60- xx12S

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 24,24 24,48 24,72 24,96 25,2 25,44 25,68 25,92 26,16 26,4 Volts

RU = 210,51 96,13 57,18 37,54 25,71 17,80 12,14 7,89 4,58 1,93 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 23,76 23,52 23,28 23,04 22,8 22,56 22,32 22,08 21,84 21,6 Volts

RD = 283,54 125,47 73,95 48,40 33,14 22,99 15,76 10,34 6,13 2,76 KOhms

RP15-, RP20, RP30-, RP60- xx12D

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 15,15 15,3 15,45 15,6 15,75 15,9 16,05 16,2 16,35 16,5 Volts

RU = 455,67 192,89 111,48 71,85 48,40 32,90 21,90 13,68 7,31 2,23 K_

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 14,85 14,7 14,55 14,4 14,25 14,1 13,95 13,8 13,65 13,5 Volts

RD = 449,01 210,22 125,38 81,89 55,46 37,68 24,92 15,30 7,80 1,78 K_

RP15-, RP20-, RP30-, RP40-, RP60- xx15S

Trim up 1 2 3 4 5 6 7 8 9 10 %

Vout = 30,3 30,6 30,9 31,2 31,5 31,8 32,1 32,4 32,7 33 Volts

RU = 306,24 129,65 75,39 49,05 33,49 23,21 15,92 10,48 6,26 2,90 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 29,7 29,4 29,1 28,8 28,5 28,2 27,9 27,6 27,3 27 Volts

RD = 300,42 142,30 85,77 56,73 39,05 27,16 18,60 12,16 7,13 3,10 KOhms

RP15-, RP20-, RP30-, RP60- xx15D


TB-1 www.recom-international.comSeptember-2004

Tubes

1.

3. 4.

2.

6.5.

www.recom-international.com TB-2September-2004

Tubes

7. 8.

10.

11.

9.

TB-3 www.recom-international.comSeptember-2004

Tubes

14.

13.

12.

www.recom-international.com TB-4September-2004

15.

Tubes

No. Types

1. RO, RM, RE, ROM, RB, RBM, RK, RH, RP, RU, RI, RD, REZ, RKZ, RUZ, RY,2. RS, RSO3. RL, RN, RF, RA, RC, RX4. RSS, RSD, RQS, RQD, RZ5. RTD, RTS, RSZ6. RV, RW, RxxPxx7. REC3-C(A), REC2.2-C(A)8. REC3, REC2.2, REC2.2-, REC3-, REC5-W(A,C)9. RAA10. RP1P5, RP03, RP05, RP08, RP1211. RP1P5-SMD, RP03-SMD, RP05-SMD, RP08-SMD12. REC10, REC1513. RP10, RP15, RP20, RP30, RP40-G14. REC20, REC3015. REC40-E

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TAPES

TA-1 September-2004

TAPES

www.recom-international.com September-2004 TA-2

Documents

DC-DC Converter Applications - RS Componentsdocs-asia.electrocomponents.com/webdocs/04ba/0900766b804bae0a.pdfDC-DC Converter Applications DC-DC Converter Applications Terminology The