Max 1617

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________________General Description

The MAX1617 (patents pending) is a precise digitalthermometer that reports the temperature of both aremote sensor and its own package. The remote sensoris a diode-connected transistortypically a low-cost,easily mounted 2N3904 NPN typethat replaces con-ventional thermistors or thermocouples. Remote accu-racy is 3C for multiple transistor manufacturers, withno calibration needed. The remote channel can alsomeasure the die temperature of other ICs, such asmicroprocessors, that contain an on-chip, diode-con-nected transistor.

The 2-wire serial interface accepts standard SystemManagement Bus (SMBus) Write Byte, Read Byte,Send Byte, and Receive Byte commands to program the

alarm thresholds and to read temperature data. The dataformat is 7 bits plus sign, with each bit corresponding to1C, in twos-complement format. Measurements can bedone automatically and autonomously, with the conver-sion rate programmed by the user or programmed tooperate in a single-shot mode. The adjustable rate allowsthe user to control the supply-current drain.

The MAX1617 is available in a small, 16-pin QSOP sur-face-mount package.

________________________Applic at ionsDesktop and Notebook Central OfficeComputers Telecom Equipment

Smart Battery Packs Test and MeasurementLAN Servers Multi-Chip Modules

Industrial Controls

____________________________Feature s

o Two Channels: Measures Both Remote and LocalTemperatures

o No Calibration Required

o SMBus 2-Wire Serial Interface

o Programmable Under/Overtemperature Alarms

o Supports SMBus Alert Response

o Accuracy:

2C (+60C to +100C, local)

3C (-40C to +125C, local)3C (+60C to +100C, remote)

o 3A (typ) Standby Supply Current

o 70A (max) Supply Current in Auto-Convert Mode

o +3V to +5.5V Supply Range

o Small, 16-Pin QSOP Package

M

AX1617

Remote/Loca l Tem perature Sensorw ith SMBus Serial Inte rface

________________________________________________________________ Maxim Integrated Products 1

MAX1617

SMBCLK

ADD0 ADD1

VCC STBY

GND

ALERT

SMBDATA

DXP

DXN INTERRUPTTOC

3V TO 5.5V

2000.1F

CLOCK

10k EACH

DATA

2N3904 2200pF

___________________Pin Configura t ion

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

N.C. N.C.

STBY

SMBCLK

N.C.

SMBDATA

ALERT

ADD0

N.C.

TOP VIEW

MAX1617

QSOP

VCC

DXP

ADD1

DXN

N.C.

GND

GND

__________Typic al Ope rat ing Circ uit

19-1265; Rev 1; 3/98

PART*

MAX1617MEE -55C to +125C

TEMP. RANGE PIN-PACKAGE

16 QSOP

EVALUATIO

NKIT

AVAILABLE

_______________Ordering Information

SMBus is a trademark of Intel Corp.

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.For small orders, phone 408-737-7600 ext. 3468.

*U.S. and foreign patents pending.

Patents Pending

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MAX161

7

Remote/Loca l Temperature Sensorw ith SMBus Serial Inte rface

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS(VCC = +3.3V, TA = 0C to +85C, unless otherwise noted.)

Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.

VCC to GND..............................................................-0.3V to +6VDXP, ADD_ to GND....................................-0.3V to (VCC + 0.3V)DXN to GND ..........................................................-0.3V to +0.8VSMBCLK, SMBDATA,ALERT,STBYto GND...........-0.3V to +6VSMBDATA,ALERTCurrent .................................-1mA to +50mADXN Current .......................................................................1mAESD Protection (SMBCLK, SMBDATA,ALERT, human body model)................................... ....... 4000V

ESD Protection (other pins, human body model)...............2000V

Continuous Power Dissipation (TA = +70C)QSOP (derate 8.30mW/C above +70C) ............ .........667mW

Operating Temperature Range .........................-55C to +125CJunction Temperature.... ..................................................+150CStorage Temperature Range .............................-65C to +165CLead Temperature (soldering, 10sec) .............................+300C

TA = +60C to +100C

Monotonicity guaranteed

ADD0, ADD1; momentary upon power-on reset

DXP forced to 1.5V

Logic inputs

forced to VCCor GND

Auto-convert mode

From stop bit to conversion complete (both channels)

VCC, falling edge

TA = 0C to +85C

VCC input, disables A/D conversion, rising edge

Auto-convert mode, average

measured over 4sec. Logic

inputs forced to VCC or GND.

CONDITIONS

A160Address Pin Bias Current

V0.7DXN Source Voltage

A8 10 1280 100 120Remote-Diode Source Current

%-25 25Conversion Rate Timing Error

ms94 125 156Conversion Time

A

120 180

35 70

Average Operating Supply Current

-2 2

Bits8Temperature Resolution (Note 1)

A

4

Standby Supply Current

3 10

mV50POR Threshold Hysteresis

V1.0 1.7 2.5Power-On Reset Threshold

C-3 3

Initial Temperature Error,

Local Diode (Note 2)

V3.0 5.5Supply-Voltage Range

V2.60 2.80 2.95Undervoltage Lockout Threshold

mV50Undervoltage Lockout Hysteresis

UNITSMIN TYP MAXPARAMETER

TR = +60C to +100C

TR = -55C to +125C

-3 3C

-5 5

Temperature Error, Remote Diode

(Notes 2 and 3)

Including long-term drift-2.5 2.5

C-3.5 3.5

Temperature Error, Local Diode

(Notes 1 and 2)

0.25 conv/sec

2.0 conv/sec

TA = +60C to +100C

TA = 0C to +85C

High levelLow level

ADC AND POWER SUPPLY

SMBus static

Hardware or software standby, SMB-

CLK at 10kHz

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0

6

3

9

12

50 5k 500k50k 5M500 50M

TEM PERATURE ERROR vs.

POWER-SUPPLY NOISE FREQUENCY

MAX1617TOC04

FREQUENCY (Hz)

TEMPERATUREERROR(C)

VIN = SQUARE WAVE APPLIED TOVCC WITH NO 0.1F VCC CAPACITOR

VIN = 250mVp-pREMOTE DIODE

VIN = 250mVp-pLOCAL DIODE

VIN = 100mVp-pREMOTE DIODE

-20

-10

0

10

20

1 10 303 100

TEMPERATURE ERROR

vs. PC BOARD RESISTANCE

MAX1617TOC01

LEAKAGE RESISTANCE (M)

TEMPERATUREERROR(C)

PATH = DXP TO VCC (5V)

PATH = DXP TO GND

-2

-1

0

1

2

-50 50 1000 150

TEM PERATURE ERROR

vs. REM OTE-DIODE TEMPERATURE

MAX1617TOC02

TEMPERATURE (C)

TEMPERATUREERROR(C)

SAMSUNG KST3904

MOTOROLA MMBT3904

ZETEX FMMT3904

RANDOMSAMPLES

__________________________________________Typical Operating Characteristics(TA = +25C, unless otherwise noted.)

MAX161

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4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)(VCC = +3.3V, TA = -55C to +125C, unless otherwise noted.) (Note 6)

Note 1: Guaranteed but not 100% tested.Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1617 device tempera-

ture is exactly +66.7C, the ADC may report +66C, +67C, or +68C (due to the quantization error p lus the +1/2C offsetused for rounding up) and still be within the guaranteed 1C error limits for the +60C to +100C temperature range. SeeTable 2.

Note 3: A remote diode is any diode-connected transistor from Table 1. TR is the junction temperature of the remote diode. SeeRemote Diode Selectionfor remote diode forward voltage requirements.

Note 4: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, itviolates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus.

Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) ofSMBCLKs falling edge.

Note 6: Specifications from -55C to + 125C are guaranteed by design, not p roduction tested.

CONDITIONS UNITSMIN TYP MAXPARAMETER

STBY, SMBCLK, SMBDATA2.2

Logic Input High Voltage V2.4

STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V V0.8Logic Input Low Voltage

ALERTforced to 5.5V A1ALERTOutput High Leakage

Current

Logic inputs forced to VCC or GND A-2 2Logic Input Current

VCC = 3V

VCC = 5.5V

ALERT, SMBDATA forced to 0.4V mA6Logic Output Low Sink Current

SMBus INTERFACE

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M

AX1617


_______________________________________________________________________________________ 5

0

10

20

30

50 5k 500k50k 5M500 50M

TEM PERATURE ERROR vs.

COMM ON-MODE NOISE FREQUENCY

MAX1617TOC05

FREQUENCY (Hz)

TEMPERATUREERROR(C)

VIN = SQUARE WAVEAC COUPLED TO DXN

VIN = 100mVp-p

VIN = 50mVp-p

VIN = 25mVp-p

-5

5

0

10

50 5k 500k50k 5M500 50M

TEMPERATURE ERROR vs.

DIFFERENTIAL-M ODE NOISE FREQUENCY

MAX1617TOC06

FREQUENCY (Hz)

TEMPERATUREERROR(C)

VIN = 10mVp-p SQUARE WAVEAPPLIED TO DXP-DXN

0

10

20

0 40 60 8020 100


DXPDXN CAPACITANCE

MAX1617TOC07

DXP-DXN CAPACITANCE (nF)

TEMP

ERATUREERROR(C)

VCC = 5V

0

100

400

200

300

500

0 10.0625 40.25 20.125 0.5 8

OPERATING SUPPLY CURRENT

vs. CONVERSION RATE

MAX1617TOC10

CONVERSION RATE (Hz)

SUPPLYCUR

RENT(A)

VCC = 5VAVERAGED MEASUREMENTS

0

5

15

25

10

20

30

35

1k 100k10k 1000k

STANDBY SUPPLY CURRENT

vs. CLOCK FREQUENCY

MAX1617TOC08

SMBCLK FREQUENCY (Hz)

SUPPLYCURRENT(A)

VCC = 5V

VCC = 3.3V

SMBCLK ISDRIVEN RAIL-TO-RAIL

0

3

60

6

20

100

0 31 42 5

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX1617TOC09

SUPPLY VOLTAGE (V)

SUPPLYCURRENT(A)

ADD0,ADD1= GND

ADD0,ADD1= HIGH-Z

0

25

100

50

75

125

T = -2 T = 8T = 0 T = 4T = 2 T = 6 T = 10

RESPONSE TO THERMAL SHOCK

MAX1617TOC11

TIME (sec)

TEMPERATU

RE(C)

16-QSOP IMMERSEDIN +115C FLUORINERT BATH

____________________________Typical Operating Characteristics (continued)(TA = +25C, unless otherwise noted.)

-5

0

5

50 5k 500k50k 5M500 50M


DIFFERENTIAL-M ODE NOISE FREQUENCY

MAX1617TOC03

FREQUENCY (Hz)

TEMPERATUREERROR(C)

VIN = 3mVp-p SQUARE WAVEAPPLIED TO DXP-DXN

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6 _______________________________________________________________________________________

______________________________________________________________Pin Descript ion

_______________Detaile d Desc riptionThe MAX1617 (patents pending) is a temperature sen-sor designed to work in conjunction with an externalmicrocontroller (C) or other intelligence in thermostat-ic, process-control, or monitoring applications. The Cis typically a power-management or keyboard con-troller, generating SMBus serial commands by bit-banging general-purpose input-output (GPIO) pins orvia a dedicated SMBus interface b lock.

Essentially an 8-bit serial analog-to-digital converter(ADC) with a sophisticated front end, the MAX1617contains a switched current source, a multiplexer, anADC, an SMBus interface, and associated control logic(Figure 1). Temperature data from the ADC is loaded

into two data registers, where it is automatically com-pared with data previously stored in four over/under-temperature alarm registers.

ADC and Multiplex erThe ADC is an averaging type that integrates over a60ms period (each channel, typical), with excellentnoise rejection.

The multiplexer automatically steers b ias currentsthrough the remote and local diodes, measures theirforward voltages, and computes their temperatures.Both channels are automatically converted once theconversion process has started, either in free-runningor single-shot mode. If one of the two channels is notused, the device still performs both measurements, andthe user can simply ignore the results of the unusedchannel. If the remote diode channel is unused, tie DXPto DXN rather than leaving the pins open.

The DXN input is biased at 0.65V above ground by aninternal diode to set up the analog-to-digital (A/D)inputs for a differential measurement. The worst-caseDXPDXN differential input voltage range is 0.25V to0.95V.

Excess resistance in series with the remote diode caus-es about +1/2C error per ohm. Likewise, 200V of off-set voltage forced on DXPDXN causes about 1C error.

SMBus Serial-Data Input/Output, open d rainSMBDATA12

SMBus Serial-Clock InputSMBCLK14

Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.Low = standby mode, high = operate mode.

STBY15

SMBus Address Select p in (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance

(>50pF) at the address pins when floating may cause address-recognition problems.

ADD16

GroundGND7, 8

SMBus Slave Address Select p inADD010

SMBus Alert (interrupt) Output, open drainALERT11

Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage aboveground.

DXN4

Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave DXP floating; tieDXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filter-ing.

DXP3

PIN

Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1F capac itor. A 200 series resistor is recom-mended but not required for additional noise filtering.

VCC2

No Connection. Not internally connected. May be used for PC board trace routing.N.C.1, 5, 9,

13, 16

FUNCTIONNAME

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AX1617


_______________________________________________________________________________________ 7

Figure 1. Functional Diagram

REMOTE

MUX

LOCAL

REMOTETEMPERATURE

DATAREGISTER

HIGH-TEMPERATURETHRESHOLD

(REMOTETHIGH)

LOW-TEMPERATURETHRESHOLD

(REMOTETLOW)

DIGITALCOMPARATOR

(REMOTE)

LOCALTEMPERATURE

DATAREGISTER

HIGH-TEMPERATURETHRESHOLD

(LOCALTHIGH)

LOW-TEMPERATURETHRESHOLD

(LOCALTLOW)

DIGITALCOMPARATOR

(LOCAL)

COMMANDBYTE

(INDEX)REGISTER

SMBDATA

SMBCLK

ADDRESS

DECODER

READ

WRITE

CONTRO

L

LOGIC

SMBUS

ADD1

ADD0

STBY

STATUSBYTEREGISTER

CONFIGURATION

BYTEREGISTER

CONVERSIONRATE

REGISTER

ALERTRESPONSE

ADDRESSREGISTER

SELECTEDVIA

SLAVEADD=0001100

AD

C

+

DIODE

FAULT

DXP

DXN

GND

VCC

- + -

+ -

88

8

8

8

8

8

8

2

7

ALERT

Q

S

R

MAX1617

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A/D Conversion Sequenc eIf a Start command is written (or generated automatical-

ly in the free-running auto-convert mode), both chan-nels are converted, and the results of bothmeasurements are available after the end of conver-sion. A BUSY status bit in the status byte shows that thedevice is actually performing a new conversion; howev-er, even if the ADC is busy, the results of the previousconversion are always available.

Remote -Diode Sele ctionTemperature accuracy depends on having a good-qual-ity, diode-connected small-signal transistor. Accuracyhas been experimentally verified for all of the deviceslisted in Table 1. The MAX1617 can also directly mea-sure the die temperature of CPUs and other integratedcircuits having on-board temperature-sensing diodes.

The transistor must be a small-signal type with a rela-tively high forward voltage; otherwise, the A/D inputvoltage range can be violated. The forward voltagemust be greater than 0.25V at 10A; check to ensurethis is true at the highest expected temperature. Theforward voltage must be less than 0.95V at 100A;check to ensure this is true at the lowest expected tem-perature. Large power transistors dont work at all.Also, ensure that the base resistance is less than 100.Tight specifications for forward-current gain (+50 to+150, for example) indicate that the manufacturer hasgood process controls and that the devices have con-sistent VBE characteristics.

For heat-sink mounting, the 500-32BT02-000 thermalsensor from Fenwal Electronics is a good choice. Thisdevice consists of a diode-connected transistor, analuminum plate with screw hole, and twisted-pair cable(Fenwal Inc., Milford, MA, 508-478-6000).

Thermal M ass and Self-Hea tingThermal mass can seriously degrade the MAX1617seffective accuracy. The thermal time constant of theQSOP-16 package is about 140sec in still air. For theMAX1617 junction temperature to settle to within +1Cafter a sudden +100C change requires about five timeconstants or 12 minutes. The use of smaller packagesfor remote sensors, such as SOT23s, improves the situ-ation. Take care to account for thermal gradientsbetween the heat source and the sensor, and ensurethat stray air currents across the sensor package donot interfere with measurement accuracy.

Self-heating does not significantly affect measurementaccuracy. Remote-sensor self-heating due to the diodecurrent source is negligible. For the local diode, theworst-case error occurs when auto-converting at the

fastest rate and simultaneously sinking maximum cur-rent at the ALERToutput. For example, at an 8Hz rateand with ALERT sinking 1mA, the typical power dissi-pation is VCC x 450A plus 0.4V x 1mA. Package thetaJ-A is about 150C/W, so with VCC = 5V and no copperPC board heat-sinking, the resulting temperature riseis:

dT = 2.7mW x 150C/W = 0.4C

Even with these contrived circumstances, it is difficultto introduce significant self-heating errors.

ADC Noise FilteringThe ADC is an integrating type with inherently goodnoise rejection, especially of low-frequency signalssuch as 60Hz/120Hz power-supply hum. Micropoweroperation places constraints on high-frequency noiserejection; therefore, careful PC board layout and properexternal noise filtering are required for high-accuracyremote measurements in electrically noisy environ-ments.

High-frequency EMI is best filtered at DXP and DXNwith an external 2200pF capacitor. This value can beincreased to about 3300pF (max), including cablecapacitance. Higher capacitance than 3300pF intro-duces errors due to the rise time of the switched cur-rent source.

Nearly all noise sources tested cause the ADC measure-ments to be higher than the actual temperature, typicallyby + 1C to +10C, depending on the frequency andamplitude (see Typical Operating Characteristics).

MAX161

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8 _______________________________________________________________________________________

CMPT3904Central Semiconductor (USA)

MMBT3904Motorola (USA)

MMBT3904

SST3904Rohm Semiconductor (Japan)

KST3904-TFSamsung (Korea)

FMMT3904CT-NDZetex (England)

MANUFACTURER MODEL NUMBER

SMBT3904Siemens (Germany)

Table 1. Remote-Sensor Transistor

Manufacturers

Note: Transistors must be diode-connected (base shorted to

collector).

National Semiconductor (USA)

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PC Board Layout1) Place the MAX1617 as close as practical to the

remote diode. In a noisy environment, such as acomputer motherboard, this distance can be 4 in. to8 in. (typical) or more as long as the worst noisesources (such as CRTs, clock generators, memorybuses, and ISA/PCI buses) are avoided.

2) Do not route the DXPDXN lines next to the deflec-tion coils of a CRT. Also, do not route the tracesacross a fast memory bus, which can easily intro-duc e + 30C error, even with good f i l tering.Otherwise, most noise sources are fairly benign.

3) Route the DXP and DXN traces in parallel and inclose proximity to each other, away from any high-voltage traces such as +12VDC. Leakage currentsfrom PC board contamination must be dealt withcarefully, since a 20M leakage path from DXP toground causes about +1C error.

4) Connect guard traces to GND on either side of theDXPDXN traces (Figure 2). With guard traces inplace, routing near high-voltage traces is no longeran issue.

5) Route through as few vias and crossunders as possi-ble to minimize copper/solder thermocouple effects.

6) When introducing a thermocouple, make sure thatboth the DXP and the DXN paths have matchingthermocouples. In general, PC board-induced ther-mocouples are not a serious problem. A copper-sol-der thermoc ouple exhib its 3V/C, and it takes

about 200V of voltage error at DXPDXN to causea +1C measurement error. So, most parasitic ther-mocouple errors are swamped out.

7) Use wide traces. Narrow ones are more inductiveand tend to pick up radiated noise. The 10 milwidths and spacings recommended in Figure 2arent absolutely necessary (as they offer only aminor improvement in leakage and noise), but try touse them where practical.

8) Keep in mind that copper cant be used as an EMIshield, and only ferrous materials such as steel workwell. Placing a copper ground plane between theDXP-DXN traces and traces carrying high-frequency

noise signals does not help reduce EMI.PC Board Layout Checklist

Place the MAX1617 close to a remote diode.

Keep traces away from high voltages (+12V bus).

Keep traces away from fast data buses and CRTs.

Use recommended trace widths and spacings.

Place a ground plane under the traces.

Use guard traces flanking DXP and DXN and con-necting to GND.

Place the noise filter and the 0.1F VCC bypass

capacitors close to the MAX1617.

Add a 200 resistor in series with VCC for bestnoise filtering (see Typical Operating Circuit).

Tw isted Pair and Shielded CablesFor remote-sensor distances longer than 8 in., or in par-ticularly noisy environments, a twisted pair is recom-mended. Its practical length is 6 feet to 12 feet (typical)before noise becomes a problem, as tested in a noisyelectronics laboratory. For longer distances, the bestsolution is a shielded twisted pair like that used for audiomicrophones. For example, Belden #8451 works well fordistances up to 100 feet in a noisy environment. Connectthe twisted pair to DXP and DXN and the shield to GND,

and leave the shields remote end unterminated.Excess capacitance at DX_ limits practical remote sen-sor distances (see Typical Operating Characteristics).For very long cable runs, the cables parasitic capaci-tance often provides noise filtering, so the 2200pFcapacitor can often be removed or reduced in value.

Cable resistance also affects remote-sensor accuracy;1 series resistance introduces about +1/2C error.

Low-Powe r Standby ModeStandby mode disables the ADC and reduces the sup-ply-current drain to less than 10A. Enter standbymode by forcing the STBYpin low or via the RUN/STOPbit in the configuration byte register. Hardware and

software standby modes behave almost identically: alldata is retained in memory, and the SMB interface isalive and listening for reads and writes. The only differ-ence is that in hardware standby mode, the one-shotcommand does not initiate a conversion.

Standby mode is not a shutdown mode. With activity onthe SMBus, extra supply current is drawn (see TypicalOperating Characteristics). In software standby mode,

M

AX1617


_______________________________________________________________________________________ 9

MINIMUM

10 MILS

10 MILS

10 MILS

10 MILS

GND

DXN

DXP

GND

Figure 2. Recommended DXP/DXN PC Traces

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the MAX1617 can be forced to perform A/D conversionsvia the one-shot command, despite the RUN/STOP bit

being high.Activate hardware standby mode by forcing the STBYpin low. In a notebook computer, this line may be con-nected to the system SUSTAT# suspend-state signal.

The STBYpin low state overrides any software conversioncommand. If a hardware or software standby command isreceived while a conversion is in progress, the conversioncycle is truncated, and the data from that conversion is notlatched into either temperature reading register. The previ-ous data is not changed and remains available.

Supply-current drain during the 125ms conversion peri-od is always about 450A. Slowing down the conver-sion rate reduces the average supply current (see

Typical Operating Characteristics). In between conver-sions, the instantaneous supply current is about 25Adue to the current consumed by the conversion ratetimer. In standby mode, supply current drops to about3A. At very low supply voltages (under the power-on-reset threshold), the supply current is higher due to theaddress pin bias currents. It can be as high as 100A,depending on ADD0 and ADD1 settings.

SMBus Digital Interfac eFrom a software perspective, the MAX1617 appears as a

set of byte-wide registers that contain temperature data,alarm threshold values, or control bits. A standardSMBus 2-wire serial interface is used to read tempera-ture data and write control bits and alarm threshold data.Each A/D channel within the device responds to thesame SMBus slave address for normal reads and writes.

The MAX1617 employs four standard SMBus protocols:Write Byte, Read Byte, Send Byte, and Receive Byte(Figure 3). The shorter Receive Byte protocol allowsquicker transfers, provided that the correct data registerwas previously selected by a Read Byte instruction. Usecaution with the shorter protocols in multi-master systems,since a second master could overwrite the commandbyte without informing the first master.

The temperature data format is 7 bits plus sign in twos-com-plement form for each channel, with each data bit repre-senting 1C (Table 2), transmitted MSB first. Measurementsare offset by +1/2C to minimize internal rounding errors; forexample, +99.6C is reported as +100C.

MAX161

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10 ______________________________________________________________________________________

ACK

7 bits

ADDRESS ACKWR

8 bits

DATA ACK

1

P

8 bits

S COMMAND

Write Byte Format

Read Byte Format

Send Byte Format Receive Byte Format

Slave Address: equiva-

lent to chip-select line ofa 3-wire interface

Command Byte: selects which

register you are writing to

Data Byte: data goes into the register

set by the command byte (to setthresholds, configuration masks, andsampling rate)

ACK

7 bits

ADDRESS ACKWR S ACK

8 bits

DATA

7 bits

ADDRESS RD

8 bits

/// PS COMMAND

Slave Address: equiva-lent to chip-select line

Command Byte: selectswhich register you arereading from

Slave Address: repeateddue to change in data-flow direction

Data Byte: reads fromthe register set by thecommand byte

ACK

7 bits

ADDRESS WR

8 bits

COMMAND ACK PS ACK

7 bits

ADDRESS RD

8 bits

DATA /// PS

Command Byte: sends com-mand with no data, usuallyused for one-shot command

Data Byte: reads data fromthe register commandedby the last Read Byte orWrite Byte transmission;also used for SMBus AlertResponse return address

S = Start condition Shaded = Slave transmission

P = Stop condition /// = Not acknowledged

Figure 3. SMBus Protocols

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Alarm Threshold Registers

Four registers store alarm threshold data, with high-temperature (THIGH) and low-temperature (TLOW) reg-isters for each A/D channel. I f ei ther measuredtemperature equals or exceeds the c orrespondingalarm threshold value, an ALERTinterrupt is asserted.

The power-on-reset (POR) state of both THIGH registersis full scale (0111 1111, or +127C). The POR state ofboth TLOW registers is 1100 1001 or -55C.

Diode Fault AlarmThere is a continuity fault detector at DXP that detectswhether the remote diode has an open-circuit condi-tion. At the beginning of each conversion, the diodefault is checked, and the status byte is updated. This

fault detector is a simple voltage detector; if DXP risesabove VCC - 1V (typical) due to the diode currentsource, a fault is detected. Note that the diode faultisnt checked until a conversion is initiated, so immedi-ately after power-on reset the status byte indicates nofault is present, even if the diode path is broken.

If the remote channel is shorted (DXP to DXN or DXP toGND), the ADC reads 0000 0000 so as not to trip either

the THIGH or TLOW alarms at their POR settings. Inapplications that are never subjected to 0C in normaloperation, a 0000 0000 result can be checked to indi-cate a fault condition in which DXP is accidentally shortcircuited. Similarly, if DXP is short circuited to VCC, theADC reads +127C for both remote and local channels,and the device alarms.

ALERTInterruptsThe ALERT interrupt output signal is latched and canonly be cleared by reading the Alert Response address.Interrupts are generated in response to THIGH and TLOWcomparisons and when the remote diode is disconnect-ed (for continuity fault detection). The interrupt does nothalt automatic conversions; new temperature data con-tinues to be available over the SMBus interface afterALERT is asserted. The interrupt output p in is open-drainso that devices can share a common interrupt line. Theinterrupt rate can never exceed the conversion rate.

The interface responds to the SMBus Alert Responseaddress, an interrupt pointer return-address feature(see Alert Response Address section). Prior to takingcorrective action, always check to ensure that an inter-rupt is valid by reading the current temperature.

Alert Response AddressThe SMBus Alert Response interrupt pointer provides

quick fault identification for simple slave devices thatlack the complex, expensive logic needed to be a busmaster. Upon receiving an ALERT interrupt signal, thehost master can broadcast a Receive Byte transmissionto the Alert Response slave address (0001 100). Thenany slave device that generated an interrupt attemptsto identify itself by putting its own address on the bus(Table 3).

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0 111 1111

DIGITAL OUTPUTDATA BITS

SIGN MSB LSB

0 111 1111+127+127.00

0 111 1111

0 111 1110+126+126.00

+127+126.50

0 001 1001

0 000 0001+1+0.50

0 000 0000

0 000 0000+0+0.00

+127+130.00

+0+0.25

+25+25.25

0 000 0000

0 000 0000+0-0.50

1 111 1111

1 111 1111-1-1.00

TEMP.(C)

-1-0.75

1 110 0111

1 110 0110-25-25.50

1 100 1001

ROUNDEDTEMP.

(C)

1 100 1001-55-55.00

+0-0.25

-55-54.75

-25-25.00

1 011 1111

1 011 1111-65-70.00

-65-65.00

Table 2. Data Format (Twos-Complement) Table 3. Read Format for Alert Response

Address (0001100)

ADD66Provide the current MAX1617slave address that was latched atPOR (Table 8)

FUNCTION

ADD55

ADD44

ADD33

ADD22

ADD11

ADD77

(MSB)

10

(LSB)Logic 1

BIT NAME

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The Alert Response can activate several different slavedevices simultaneously, similar to the I2C General Call.If more than one slave attempts to respond, bus arbitra-tion rules apply, and the device with the lower address

code wins. The losing device does not generate anacknowledge and continues to hold the ALERT line lowuntil serviced (implies that the host interrupt input islevel-sensitive). Successful reading of the alertresponse address c lears the interrupt latch.

Command Byte FunctionsThe 8-bit command byte register (Table 4) is the masterindex that points to the various other registers within theMAX1617. The registers POR state is 0000 0000, sothat a Receive Byte transmission (a protocol that lacksthe command byte) that occurs immediately after PORreturns the current local temperature data.

The one-shot command immediately forces a new conver-

sion cycle to begin. In software standby mode(RUN/STOP bit = high), a new conversion is begun, afterwhich the device returns to standby mode. If a conversionis in progress when a one-shot command is received, thecommand is ignored. If a one-shot command is receivedin auto-convert mode (RUN/STOP bit = low) between con-versions, a new conversion begins, the conversion ratetimer is reset, and the next automatic conversion takesplace after a full delay elapses.

Configuration Byte FunctionsThe configuration byte register (Table 5) is used tomask (disable) interrupts and to put the device in soft-ware standby mode. The lower six bits are internally set

to (XX1111), making them dont care bits. Write zerosto these bits. This registers contents can be read backover the serial interface.

Status Byte FunctionsThe status byte register (Table 6) indicates which (ifany) temperature thresholds have been exceeded. Thisbyte also indicates whether or not the ADC is convert-ing and whether there is an open circuit in the remotediode DXPDXN path. After POR, the normal state of allthe flag bits is zero, assuming none of the alarm condi-tions are present. The status byte is cleared by anysuccessful read of the status byte, unless the fault per-sists. Note that the ALERT interrupt latch is not auto-

matically cleared when the status flag b it is cleared.When reading the status byte, you must check for inter-nal bus collisions caused by asynchronous ADC timing,or else disable the ADC prior to reading the status byte(via the RUN/STOP bit in the configuration byte). Inone-shot mode, read the status byte only after the con-version is complete, which is 150ms max after the one-shot conversion is commanded.

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Table 4. Command-Byte Bit Assignments

*If the device is in hardware standby mode at POR, both temperature registers read 0C.

Read remote temperature: returns latest temperatureRRTE 01h

00h

COMMAND

0000 0000*

0000 0000*

POR STATE

Read configuration byteRCL 03h

02h

0000 0000

N/A Read status byte (flags, busy signal)RSL

Read local THIGH limitRLHN 05h

Read local temperature: returns latest temperatureRLTS

04h

0111 1111

0000 0010

Read remote THIGH limitRRHI 07h

06h

0111 1111

1100 1001 Read local TLOW limitRLLI

Read conversion rate byte

REGISTER

RCRA

Write configuration byteWCA 09h

08h

N/A

1100 1001

FUNCTION

Write local THIGH limitWLHO 0Bh

0Ah

N/A

N/A Write conversion rate byteWCRW

Write remote THIGH limitWRHA 0Dh

Read remote TLOW limitRRLS

0Ch

N/A

N/A

One-shot command (use send-byte format)OSHT 0Fh

0Eh

N/A

N/A Write remote TLOW limitWRLN

Write local TLOW limitWLLM

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To check for internal bus collisions, read the statusbyte. If the least significant seven bits are ones, discard

the data and read the status byte again. The status bitsLHIGH, LLOW, RHIGH, and RLOW are refreshed on theSMBus clock edge immediately following the stop con-dition, so there is no danger of losing temperature-relat-ed status data as a result of an internal bus collision.The OPEN status bit (diode continuity fault) is onlyrefreshed at the beginning of a conversion, so OPEN

data is lost. The ALERTinterrupt latch is independent ofthe status byte register, so no false alerts are generat-ed by an internal bus collision.

When auto-converting, if the THIGH and TLOW limitsare close together, its possible for both high-temp andlow-temp status bits to be set, depending on theamount of time between status read operations (espe-cially when converting at the fastest rate). In these cir-cumstances, its best not to rely on the status bits toindicate reversals in long-term temperature changesand instead use a current temperature reading to

establish the trend direction.

Conversion Rate ByteThe conversion rate register (Table 7) programs thetime interval between conversions in free-running auto-convert mode. This variable rate control reduces thesupply current in portable-equipment applications. Theconversion rate bytes POR state is 02h (0.25Hz). TheMAX1617 looks only at the 3 LSB bits of this register, sothe upper 5 bits are dont care bits, which should beset to zero. The conversion rate tolerance is 25% atany rate setting.

Valid A/D conversion results for both channels areavailable one total conversion time (125ms nominal,

156ms maximum) after initiating a conversion, whetherconversion is initiated via the RUN/STOP bit, hardwareSTBY pin, one-shot command, or initial power-up.Changing the conversion rate can also affect the delayuntil new results are available. See Table 8.

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RUN/STOP

6 0

0

PORSTATE

Standby mode controlbit. If high, the deviceimmediately stops con-verting and enters stand-by mode. If low, thedevice converts in eitherone-shot or timer mode.

Masks allALERTinter-rupts when high.

FUNCTION

RFU50 0 Reserved for future use

MASK7 (MSB)

BIT NAME

Table 5. Configuration-Byte Bit

Assignments

Table 7. Conversion-Rate Control Byte

Table 6. Status-Byte Bit Assignments

*These flags stay high until cleared by POR, or until the status

byte register is read.

LHIGH*6A high indicates that the local high-temperature alarm has activated.

A high indicates that the ADC is busyconverting.

FUNCTION

LLOW*5A high indicates that the local low-temperature alarm has activated.

RHIGH*4A high indicates that the remote high-temperature alarm has activated.

RLOW*3 A high indicates that the remote low-temperature alarm has activated.

OPEN*2A high indicates a remote-diode conti-nuity (open-circuit) fault.

RFU1

BUSY7

(MSB)

Reserved for future use (returns 0)

RFU0

(LSB)Reserved for future use (returns 0)

BIT NAME

0.12501h 33

30

0.2502h 35

0.503h 48

104h 70

205h 128

406h

0.062500h

225

807h 425

RFU08h to

FFh

DATACONVERSION

RATE(Hz)

AVERAGE SUPPLYCURRENT

(A typ, at VCC = 3.3V)

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Slave AddressesThe MAX1617 appears to the SMBus as one devicehaving a common address for both ADC channels. Thedevice address can be set to one of nine different val-ues by pin-strapping ADD0 and ADD1 so that more

than one MAX1617 can reside on the same bus withoutaddress conflicts (Table 9).

The address pin states are checked at POR only, andthe address data stays latched to reduce quiescentsupply current due to the bias current needed for high-Zstate detection.

The MAX1617 also responds to the SMBus AlertResponse slave address (see the Alert ResponseAddresssection).

POR and UVLOThe MAX1617 has a volatile memory. To prevent ambigu-ous power-supply conditions from corrupting the data inmemory and causing erratic behavior, a POR voltage

detector monitors VCC and clears the memory if VCC fallsbelow 1.7V (typical, see Electrical Characteristics table).When power is first applied and VCC rises above 1.75V(typical), the logic blocks begin operating, although readsand writes at VCC levels below 3V are not recommended.A second VCC comparator, the ADC UVLO comparator,prevents the ADC from converting until there is sufficientheadroom (VCC = 2.8V typical).

Power-Up Defaults:

Interrupt latch is cleared. Address select pins are sampled.

ADC begins auto-converting at a 0.25Hz rate.

Command byte is set to 00h to facilitate quickremote Receive Byte queries.

THIGH and TLOW registers are set to max and minlimits, respectively.

Table 8. RLTS and RRTE Temp Register Update Timing Chart

n/a (0.25Hz)

NEW CONVERSION RATE(CHANGED VIA WRITE TO

WCRW)

Power-on resetAuto-Convert

OPERATING MODE CONVERSION INITIATED BY:

156ms max

TIME UNTIL RLTS AND RRTEARE UPDATED

156ms maxn/a1-shot command, while idlingbetween automatic conversions

Auto-Convert

When current conversion iscomplete (1-shot is ignored)

20sec

n/a

0.0625HzRate timerAuto-Convert

1-shot command that occursduring a conversion

Auto-Convert

10sec

5sec

0.125Hz

0.25HzRate timerAuto-Convert

2.5sec

1.25sec

0.5Hz

1HzRate timerAuto-Convert

Rate timerAuto-Convert


625ms

312.5ms

2Hz

4HzRate timerAuto-Convert

237.5ms

156ms

8Hz

n/aSTBYpinHardware Standby



156ms

156ms

n/a

n/a1-shot commandSoftware Standby

RUN/STOP bitSoftware Standby

Table 9. Slave Address Decoding (ADD0and ADD1)

Note: High-Z means that the pin is left unconnected and floating.

0011 001High-ZGND

0011 000

ADDRESS

0101 001GNDHigh-Z

0011 010VCCGND

0101 011VCCHigh-Z

0101 010

1001 101High-ZVCC

1001 100

GNDGND

GNDVCC

High-ZHigh-Z

1001 110VCCVCC

ADD0 ADD1

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Figure 5. SMBus Read Timing Diagram

Figure 4. SMBus Write Timing Diagram

SMBCLK

A B C D E F G H I J K

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tHD:DAT tSU:STO tBUF

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVEE = SLAVE PULLS SMBDATA LINE LOW

L M

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO SLAVE

H = LSB OF DATA CLOCKED INTO SLAVE

I = SLAVE PULLS SMBDATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO MASTER

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION, DATA EXECUTED BY SLAVE

M = NEW START CONDITION

SMBCLK

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

A B C D E F G H I J

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tSU:STO tBUF

K

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = ACKNOWLEDGE CLOCK PULSE

J = STOP CONDITION

K = NEW START CONDITION

Programming Exam ple:Clock-Throttling Control for CPUs

An untested example of pseudocode for proportional

temperature control of Intel mobile CPUs via a power-management microcontroller is given in Listing 1. Thisprogram consists of two main parts: an initialization rou-tine and an interrupt handler. The initialization routinechecks for SMBus communications problems and setsup the MAX1617 configuration and conversion rate. Theinterrupt handler responds toALERTsignals by readingthe current temperature and setting a CPU clock duty

factor proportional to that temperature. The relationshipbetween clock duty and temperature is fixed in a look-up table contained in the microcontroller code.

Note: Thermal management decisions should be madebased on the latest temperature obtained from theMAX1617 rather than the value of the Status Byte. TheMAX1617 has a very quick response to changes in itsenvironment due to its sensitivity and its small thermalmass. High and low alarm conditions can exist in theStatus Byte due to the MAX1617 correctly reportingenvironmental changes around it.

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Listing 1. Pseudocode Example

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Listing 1. Pseudocode Example (continued)

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Listing 1. Pseudocode Example (continued)

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QSOP.E

PS

________________________________________________________Pa ckage Information

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NOTES

Documents

Max 1617