LED Seminar (Elko - Julio 2012)

8/13/2019 LED Seminar (Elko - Julio 2012)

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STMicroelectronics

All trademarks and logos are the property of their respective owners. All rights reserved. They are used here only as conceptual examples.

LED Seminar


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Contents

1.1. LED BasicsLED Basics

2.2. Driving High BrightnessDriving High Brightness LEDsLEDs in General Lightingin General Lighting

OffOff--line LED Driversline LED Drivers

DCDC--DC converters based solutionsDC converters based solutions

3.3. LED driving solutions for SignageLED driving solutions for Signage

4.4. LED driving solutions for LCD BacklightingLED driving solutions for LCD Backlighting


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Contents








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LEDs Advantages & Drawbacks

Why LEDs?

High Efficiency (energy/TCO cost saving)

Environment Friendly (CO2 saving, mercury free, recyclable, etc)

Reliable (long life span)

Better Light Quality (CRI, directed light output)

Indestructible (shock, vibration)

Smaller Size, Light Weight

Fast Response (solid state lighting, easly dimmable) Ambient Lighting Effects, etc..

LEDs drawbacks?

Thermal Management Cost ($/Lumens)

Standardization

The

LED

Potential


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LED Driving Circuit: Basics

A LED Driving circuit is a type of power conversion circuit featuring two maincharacteristics:

Delivers a constant average current to the load under all conditions

(eg. input voltage change, temperature change, VF change)instead of constant voltage

Keeps ripple current at acceptable level under all conditions


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Driving Techniques

Resistor LimitingStrenght: Inexpensive, SimpleWeakness: Current variation as VF changesPoor efficiencyHeat generation on the current limiting resistor

Application: Low Power LEDs where brightnessresolution is not an issue

Linear Control MethodStrenght: Simple, high current accuracyWeakness: Poor efficiencyHeat dissipation on the driver ICApplication: EMI sensitive designs and projects

where the drop between VIN and VF is minimum.

Switching Control Method

Strenght: High Efficiency, high current accuracyWeakness: Relatively expensive, Circuit complexityApplication: Where heat and efficiency is an issue.

VFVIN+-

IF

R

R

VVI FINF

=

VIN+-

FeedbackR

L

VIN+- Control &

Feedback R


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Display and signFull color video

Monochrome message boards

Variable message signs

Transportation - passengerInformation

IlluminationArchitectural lighting

FlashlightsMachine vision

General illumination

Sign and marker lights

Neon and bulb replacement

Interior decoration lighting

LED BacklightingNotebookNetbookLCD PanelsGeneral backlighting

STCF0xLED770xPM660x

Traffic signalsRoad traffic signals

Aviation

Railway

Navigation

Emergency/police signals

Automotive & ConsumerInterior/ Exterior lighting

Consumer electronics

TelevisionsVCR/DVD/stereo/audio/video devices

Household appliances

Toys/games

Security equipment

LEDs Applications


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ResidentialLighting

Residential &CommercialLighting

VIPer12A/15/17 (Flyback)

+

TSM10xx

OutputPower*

[W]

Non-Isolated Isolated

10

25

100

L6562A/AT/3H (HPF)

+

DC/DC for each LED string

L6562A/AT/3H (PFC-Boost)+

L6565/6 (Q.R. Controller)+


L6562A/AT/3H (PFC-Boost)+

L6599A/AT (Resonant Controller)+


VIPerX2A/16 (Buck)

VIPer53-E (Buck)

VIPer22A-E/25/27/53-E (Flyback)

+

TSM10xx

VIPerX2A//X7 (N.I. Flyback)

+

TSM10xx

L6562A/AT

(Modified Buck Converter)

L6562A/AT/3H (PFC-Boost)

+L6562A/AT

(Modified Buck Converter)

Off-Line LED Drivers: ST Solutions Offering

L6562A/AT

(Buck-Boost)

Architectural& StreetLighting

* Output power referred to wide input voltage range


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Street lights represent an attractive application for LEDlighting due to several factors.

Large number of streetlights

High maintenance costs due to height andlocation over public roadways

Growing pressure for green lighting solutions toreduce CO2 emissions

Desire for white light

Benefits of LEDs in Street Lighting Longer lifespan and reduced maintenance costs over the expected practical lifetime of the

luminaries (~15 years)

An LED system, thanks to its directionality, illuminates more effectively the target area andthus significantly reduces inefficiencies due to unwanted or not useful lighted areas.

Energy savings level of about 13% relative to the assumed 250W HPS baseline

Improved night visibility due to better Color Rendering Index, higher color temperature andincreased illuminance uniformity

The "instant-on/instant-off" and dimming capability of LEDs offer additional intrinsic valuethrough control strategies that can brighten and dim based on time of day, ambient light, orany other control parameters desired.

Using LEDs in Street Lighting


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ST addresses the application with a solution based on PFC+LLC

ac mains

85305 Vac

48 V/130W

PFCL6562AT LLCL6599AT

AC DC90W 250W

L6562AT and L6599ATare guaranteed over -40 to +125 degrees

making them suitable for reliable power supply with very aggressive

form factor easily fitting all the current street lamp solutions.

R LED

Modified

Buck CC

regulator

DIMMING

R LED

Modified

Buck CC

regulator

DIMMING

LED Street Light : ST solution


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EVALUATION BOARD(http://www.st.com/evalboards)

Functionalities:Input voltage 48V (+/- 20%)Output current (average): 0.35AOutput ripple current < 140mA (+/- 20%)Output current setting / calibration

Digital dimmingOpen / Short circuit protectionNo electrolytic capacitor

ST Solution: EVL6562A-LED

Key Products:

L6562A STPS2H100A

STN3NF06

Typical Applications:

Street lighting Interior lighting Decorative lighting General lighting

Purpose & Positioning:

It addresses customers working on lightingapplications using high brightness LEDs, whereenergy saving, long life time, robustness,brightness regulation and of course very highluminous efficiency is required. It is suitable forhigh input DC voltage LED drivers

Constant current modified Buck LED driver using the L6562AConstant current modified Buck LED driver using the L6562A


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Modified buck converter - measurement

Measurement at nominal input voltage 48V with the output voltage V_led as a parameter

LED current (average, minimum, maximum) LED ripple current

Switching frequencyEfficiency


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Vin = 88V to

265V ac

Input Filter

Microcontroller

ST7LITEU05

PF controller

L6562A PF controller

L6562A

PWM GENERATOR

MODIFIED BUCK CONVERTERHIGH POWER FACTOR BOOST CONVERTER

Brightness Control

400V 80W LOAD

HIGH POWER FACTOR BOOST CONVERTER: Transition mode operation Wide input voltage range 88V to 265V ac

Regulated output voltage 400V

MODIFIED BUCK CONVERTER: Continuous conduction mode operation Fix Off Time (FOT) network designed LED current setting 350mA, 700mA and 1A

Design features:

STTH1L06

STP8NM50FPSTPSC806D

STF9NM50N

PWM GENERATOR: PWM frequency 250Hz 0% to 100% DC variation Input voltage 3.3V to 35V

PWM GeneratorOrdering code:

STEVAL-ILL013V2

Off-line LED driver : ST solution


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Functionalities:80W LED driverLED current setting to 350mA, 700mA and 1AHigh efficiency (~90%) and high Power FactorWide input voltage range 88V to 265V ACUniversal PWM input for dimming (ext. board required)

Not isolated SMPSBrightness regulation between 0% and 100%EMI filter implementedEN55015 and EN61000-3-2 compliant

ST Solution: STEVAL-ILL013V1

Key Products:

L6562A STTH1L06A

STF9NM50N

STP8NM50

STPSC806D

BUX87


Street lighting Interior lighting Decorative lighting


It addresses customers working on high endlighting applications using high brightness LEDs,where energy saving, long life time, robustness,brightness regulation and very high luminousefficiency is required. Main leading application isthe street lighting.

80W off-line LED driver with dimming based on L6562A80W off-line LED driver with dimming based on L6562A


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STEVAL-ILL013V1 Measurement

LOAD: LE UW E3B - OSTAR LED FROM OSRAMPower Factor

0

0.2

0.4

0.6

0.8

1

85 100 110 120 140 160 180 200 220 230 240 265

Input voltage [V]

Powerfactor[-]

700mA@6LEDs

350mA@12LEDs

1A@4LEDs

Power Factor - zoom

0.95

0.96

0.97

0.98

0.99

1

85 100 110 120 140 160 180 200 220 230 240 265

Input voltage [V]

Powerfactor[-]

700mA@6LEDs

350mA@12LEDs

1A@4LEDs

THD

0.00

2.00

4.00

6.00

8.00

10.00

12.00

85 100 110 120 140 160 180 200 220 230 240 265

Input voltage [V]

TH

D[%]

700mA@6LEDs

350mA@12LEDs

1A@4LEDs

Efficiency

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

85 100 110 120 140 160 180 200 220 230 240 265

Input voltage [V]

Efficiency[%]

700mA@6LEDs

350mA@12LEDs

1A@4LEDs

NOTE: Efficiency measured with PWM generator


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ac mains

88 264 Vac

48 V bus

R LED G LED B LED

L6562AModified Buck

CC regulator

L6562AModified Buck

CC regulator

L6562AModified Buck

CC regulator

L6562A

High-PF FlybackConverter

DIMMING DIMMING DIMMING

Modified Buck CC regulator block: reduced component count in case of customization

Up to 50W Applications: Transition Mode PFCin Isolated Flyback and Modified Buck Topology


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Functionalities:Input voltage 48V (+/- 20%)Output current (average): 0.35AOutput ripple current < 140mA (+/- 20%)Output current setting / calibration

Digital dimmingOpen / Short circuit protectionNo electrolytic capacitor


Key Products:

L6562AD, STTH1R06U,

P6KE300A,

STTH3R02S

STPS1H100A

STTH102A

STP7NK80ZFP

STS4NF100

TL431AID


Decorative lighting Multicolor lighting Wall washing Street Lighting


It shows an innovative solution for multiple stageLED driving when PF, isolation and individual LEDbrightness regulation are required

32W offline RGGB LED driver with individual LEDchannel brightness regulation

32W offline RGGB LED driver with individual LEDchannel brightness regulation

Functionalities: Line voltage range: 88 to 265 VAC 4 channels LED driver Constant LED current 350mA LOAD: 5 to 13 LEDs per each channel Rated output power: 32W (wide voltage range) Rated output power: 42W (EU voltage range)

Isolated SMPS Individual RGGB brightness regulation EN55015 and EN61000-3-2 compliant PCB double-side, 145 x 75 x 27 mm

Demoboard available in Q4/Q1Demoboard available in Q4/Q1


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STEVAL-ILL019V1 Measurement: PF, THD and efficiency

Power Factor

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

90 110 130 150 170 190 210 230 250 265

Input voltage [V]

PowerFactor[-]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

30 LEDs

20 LEDs

Power Factor - zoom

0.8

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

90 110 130 150 170 190 210 230 250 265

Input voltage [V]

PowerFactor[-]

0.8

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

30 LEDs

20 LEDs

THD

0

2

4

6

8

10

12

14

16

18

90 110 130 150 170 190 210 230 250 265

Input voltage [V]

TH

D[%]

0

2

4

6

8

10

12

14

16

18

30 LEDs

20 LEDs

Efficiency

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

90 110 130 150 170 190 210 230 250 265

Input voltage [V]

Efficiency[%]

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

30 LEDs

20 LEDs

LOAD: 30LEDs (9 blue LBW5SN; 6 + 7 green LTW5SN; 8 red LRW5SN)

LOAD: 20LEDs (5 blue LBW5SN; 4 + 4 green LTW5SN; 7 red LRW5SN)


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STEVAL-ILL019V1 Measurement: LED current precision

Modified buck converter current precision

0

50

100

150

200

250

300

350

400

450

12.1 15 17.9 20.8 23.7 26.7 29.7 32.7 35.6 38.7

V led [V]

Iled[mA]

I led

4 5 6 7 8 9 10 11 12 13 LEDs

Output LED precision Iout = 350mA 5%(5LEDs to 13LEDs)

LED average current 350mASwitching frequency 189kHz

LED peak to peak current ripple 57.8mA

LED voltage vs. LED current LED current measurement


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Off-line TRIAC dimmable LED driver : ST Solution

LED driver solution compatible with TRIAC phase-control dimmers

The undimmed power factor is an excellent 0.95

TRIAC based dimmers

Conventional "2-wire" dimmers replace wall switchesin some applications. It is highly desirable to have theLED driver accept power from a TRIAC-dimmedsource. The TRIAC dimmer limits the average powerdelivered to the load (LED driver) during each half

cycle by increasing the turn on delay hence theconduction angle of TRIAC.

Many LED drivers have stickers stating "not for usewith dimmers" because they are unable to cope withthe sudden rise of voltage late in the half cycle

This solution has characteristics compatible with thetriac dimmer. It features the (approximately)sinusoidal line current when the driver is not dimmed,and the line current when the triac dimmer (set nearmaximum) is in the circuit.


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15W off-line TRIAC dimmable LED driver based onL6562AD and TSM1052 (USA Market - 115 V)15W off-line TRIAC dimmable LED driver based onL6562AD and TSM1052 (USA Market - 115 V)

Application note: AN2711Demoboard available in Q4/Q1

Application note: AN2711Demoboard available in Q4/Q1

Functionalities: 120 V line (96 V to 132 Vrms) Vout is set at 40 V max Iout is set at 0.7 A maximum average current 0.7 minimum power factor, required for residential use 0.9 or greater power factor, required for commercial use Capable of FCC Class B conducted EMI

Emitted acoustic noise less than 24 dBA Isolated output, "safe" voltage Dimmable with low-cost TRIAC based dimmer, average current down to

less than 10% of maximum LED current Meets US DOE ENERGY STAR program requirements for SSL

luminaires - version 1.0.

Key Products:

L6562ADSTPS10150CT

STP5NK60ZFP

TSM1052

AN2711


Residential lighting Commercial lighting

Purpose & Positioning: To give to luminaire manufacturers a low-cost,commonly available dimming option for homefixtures


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Efficiency measurement

A high efficient LED driving system is mandatory in order to maximizeillumination efficiency and reduce power dissipation

Efficiency measurements - Vin = 120 Vac Efficiency vs. conduction angle

Efficiency of the board at full load with no dimmer is 82.47%


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Functionalities:Input voltage 48V (+/- 20%)Output current (average): 0.35AOutput ripple current < 140mA (+/- 20%)Output current setting / calibrationDigital dimmingOpen / Short circuit protectionNo electrolytic capacitor


Key Products:

L6562A STD5NM50

STTH1L06A

Typical Applications: General lighting Residential lighting

Purpose & Positioning:Suitable for solid state lighting solution whichrequires high power factor, high efficiency in thesimplest way and at the lower cost

18W single stage off-line LED driver based on L6562A18W single stage off-line LED driver based on L6562A

40mm

Functionalities: Buck-Boost topology Input voltage: 120VAC +/-10% Provides 18W constant power to HBLED Able to drive 14 to 20 HBLED in series Open load and short load protection

Soft-switching Power Factor > 0.8 Efficiency > 87% RoHS Compliant


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STEVAL-ILL026V1 - measurement

Cost effective and compact solution

The circuit is able to protect itself from abnormal condition of open load operation

In case of short circuit condition the VIPer works at minimum admissible duty cycle until thevoltage applied to the Vdd pin falls below the shutdown voltage

Board efficiency vs input voltageLED current regulation vs input voltage


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Off-line LED drivers: Evaluation boards summary (1/2)

Solutions available and technical documentations

P/N Order Code Vin (VAC) Iout (mA) Vout (VDC) Comments AN

VIPER12A (*) STEVAL-ILL005V1 85 to 265350 & 700 &

10503.5 to 15

Flyback constantcurrent source

AN1916

VIPER22A (*) STEVAL-ILL001V185 to 135 or185 to 265

350 3.5 to 28Flyback

dimmableAN2042

VIPER17HN(*) STEVAL-ILL017V1 176 to 265 500 7 VmaxNot Isolated

Flyback constantcurrent source

AN2811

VIPER22A STEVAL-ILL026V1 85 to 265 350 0 to 40Buck constantcurrent source

AN2961

(*) plus TSM10x


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Off-line LED drivers: Evaluation boards summary (2/2)

Solutions available and technical documentations

DRAFT18W single stage

off-line LEDdriver

54V350mA120Vac10%STEVAL-ILL027V1L6562A

DRAFT32W off-line

RGGB LED driver48V4x350mA85 to 265STEVAL-ILL019V1L6562A

DRAFT130W PFC Boost+ LLC LED SMPS

48V2.7A85 to 305EVL130W-STRLIGL6562AT

L6599AT

P/N Order Code Vin (VAC) Iout (mA) Vout (VDC) Comments AN

L6562A STEVAL-ILL016V2 120Vac20% 700mA 40Vmax15W HP Flybackconstant current

sourceAN2711

L6562A EVL6562A-35WFLB 90 to 265 700mA 48V35W HP Flybackconstant current

source

AN2838

L6562A STEVAL-ILL013V1 85 to 265350mA, 700mA

or 1A400V

80W PFC Boost +Modified buck

converter

AN2928

UM0670


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Contents








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LED Driver Concept using DC-DC Converters

Basic Topologies

BOOST: (Vin


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Basic topologies: Boost

BOOST VOUTVIN

VREF

L6920DLED7706

LED7707

PM6600

STLD41 (in development)

Supported by:

Low-side switch

Low-side current sensing Load referenced to GND

+

=

121

1

2

, rDD

II LEDRMSSW

DVV INOUT

=

1

1

( )2

1 DfLI

Vr

LED

OUT

=

ISW

OUT

INOUT

V

VVD =**

DII

OUTSW

=1

1

** DREAL>DIDEAL in the formula to compensate for losses. Always check the real duty cycle.


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Positive Buck-Boost High-side switch

VIN VOUT

VREF

Supported by:


Basic topologies: Positive Buck-Boost

+

=

121

1

2

, rDD

II LEDRMSSW ( )2

1 DfLI

Vr

LED

OUT

=

ISW

D

DVV INOUT

=1 D

IIOUTSW

=1

1

INOUT

OUT

VV

VD+

=**


L497X L597X L598X L6902 L6928

STCF07

Require external FET


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Inverting Buck-Boost High-side switch

VIN VOUT

VREF Supported by:

High-side current sensing Load referenced to GND

Basic topologies: Inverting Buck-Boost

Negative output

+

=

121

1

2

, rDD

II LEDRMSSW

D

DVV INOUT

=1

( )2

1 DfLI

Vr

LED

OUT

=

ISW

INOUT

OUT

VVVD+

=**

DII

OUTSW

=1

1


L497X L597X L598X L6902


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Basic topologies: SEPIC (Buck-Boost)

LED7706

LED7707

Supported by:

Low-side switch

Low-side current sensing Load referenced to GNDSEPIC VOUTVIN

VREF

2,

)(

IN

INOUTOUTOUTRMSSWV

VVVII

+

ISW

IOUT

D

DVV INOUT

=1 INOUT

OUT

VVVD+

=**

DII

OUTSW

=1

1



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Basic topologies: Conventional Buck

Conventional BUCK High-side switchVIN VOUT

VREF

Supported by:


L597X

L598X L6902

L6925/6/8

+=

121

2

, rDII LEDRMSSW

DVV INOUT =

( )DfLI

V

rLED

OUT

= 1

ISW

IN

OUT

V

VD =**OUTSW

II =


ST1S10

PWM controller (L6726A)+ FETs


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Functionalities: Buck topology Input voltage Vin: 8 V to 30 Vdc Designed for 350mA LEDs Fully dimmable board Easy modification for higher current Analog dimming

Digital (PWM) dimming Maximum output voltage limited 5 LEDs can be driven with 700mA output current (Vf = 4.4V) 6 LEDs can be driven with 350mA output current (Vf = 4V)


Key Products:

L6902D STPS340U

Typical Applications: Architectural lighting

General Lighting Gaming Machine

Purpose & Positioning: An high efficiency switching buck

converter current source able to supplyHigh Brightness LEDs. To provide a tool to test and evaluate theL6902D as LED driver with analog andPWM dimming functionality

High-intensity LED driver with dimming based on L6902High-intensity LED driver with dimming based on L6902


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Functionalities: Buck topology Input voltage Vin: 8V to 18V Output voltage (with Vin= 18 V): 2.5V to 14 V Output current ILED: 1A / 1.5A / 2.8A Analog dimming (with ILED= 0 A) : 0V to 2.5V

Low level PWM signal: 0 V High level PWM signal: 2.8V to 3.8V (typ.: 3.3V) Duty cycle (at fdim = 200 Hz) : 0% to 99% Efficiency (with Vin =18 V and Vout = 12.6V): 94.8%


Key Products:

L6726A L78L06ACU

STS8DNH3LL

STPS1l30A

TS821B

Typical Applications: General lighting

Architectural lighting Decoration lighting Reading lighting Cabinet Lighting

Purpose & Positioning: For customers working with LEDs

applications which need high currentsolutions. Typical example could be P7from SEOUL-Semiconductor.

High Efficiency Switching LED Driver for High CurrentLEDs based on L6726A

High Efficiency Switching LED Driver for High CurrentLEDs based on L6726A


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Boot 1

Ugate 2

GND

3

Lgate 4

Vcc

5

FB6

COMP7

Phase

8

U2 L6726A

22uFC1

2R2

R7

2R2

R8

GND

10uH

L1

Inductor

22uFC9

0R56R9

D1TS821

4k7R4

4k7

R3

6k8R5

82nFC3

470pFC2

1k1R2

100nFC7

D3STPS1L30M

D2

1N4148

10RR610uF

C4

4.7uFC8

100nFC6

IN3

2

OUT 1

GND

U1 L78L06AC

8

2

1

5

4

3

7

6

Q1STS8DNH3LL

0R56R10

62k

R1

100nF

C5

Vcc18V

CompPhase

Vcc6V

Boot

OUT-A

OUT-K

PWM

Vref

Ugate

Lgate

FB

123

PWM

123456

OUT

0R56R14

0R3R15

0R3R16

1 2 3

P1

1

32

K375A

CN1

8-18V

STEVAL- ILL023V1: Electrical Schematic

Power mosfet

STS8DNH3LL

PWM controller

L6726A

Linear regulator

L78L06AC

Schotkky diode

STPS1L30MVoltage reference

TS821


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Power losses on the

sense resistor

Ploss = VFB * ILED

Ploss = 0.8V * 2.8A

Ploss = 2.24W

Ploss = 0.28V * 2.8APloss = 0.784W

Losses on Rsen

2.24 W

-65%

0.784W

FB

Rsen

GND

VCC

0.8V

2.8A

Ploss

FB

Rsen

GND

VCC

0.8V

2.8A

PlossR2

R1

TS821

1.225V

0.28V

Classic

current sensing

Current sensingwith offset

STEVAL-ILL023V1 Current Sensing


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STEVAL-ILL023V1: Efficiency 94.8% at full load

Main efficiency factors Synchronous rectification

Decreased feedback voltage from 0.8V to 0.28V

Mosfet with Rdson 20m

Inductor with DC resistance 7.8m


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STCF07: Buck-Boost White LED Driver

Features Drives one power LED up to 1A

Input Voltage range: 2.3V to 5.5V

LED temperature protection with NTC

Open LED failure detection

1.8 MHz typ fixed frequency PWM Synchronous rectification

90% typ. efficiency across all input voltage range

Two selectable operational modes:

High current mode: Up to 1A

Low current mode: from 20mA

Adjustable current in both modes

True shutdown

OVP(5.3V), OTP, SCP

< 1A shutdown current

QFN 4 x 4 x 1 mm 16 leads

Typical Application LED Flashlight Camera flash

VLX1

PV BAT

VBAT

EN

CSEL

GND PGND

FB2

FB1

RLC

RHC

COUT

L

CIN

VIN

STCF07

VLX2VLX1

FAULT

VOUT

FB2S

RX NTC

RXNTC


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Principle of a Linear Current Regulator

Very similar to a voltage regulator,linear current driving uses a linearpass element with a feedback blockthat regulates the current in a pathrather than the voltage at a node.

Devices can be operated as currentsource or current sink

Linear current driving can only beused when the input voltage isalways higher than the output

voltage. Headroom must also beadded for the voltage drop in thedriver circuits. Otherwise there is notenough voltage available to operatethe LEDs.

Advantages: simple design, low

component cost. Drawbacks: Low efficiency, heat

dissipation on the IC.

LEDsupplydriver VnVV =

LEDdriverdriver IVP *=


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STCSXX/A: Linear LED driver

Main features: Up to 40V operating input voltage Less than 0.5 V voltage overhead PWM dimming pin Shutdown pin

Open LED failure detection A Version: slope compensation

for EMI improvement

STCS05 features: Up to 0.5 A output current

SO-8 package

STCS1 features: Up to 1.5 A output current

DFN8 & Power SO-8 package

STCS2 features: Up to 2 A output current PowerSO-10 package

Input Voltage

PWM

ENGNDSLOPE

VCC DRAIN

Load Disconnection

DISC FB

STCS05/1/2/A

Input Voltage

PWM

ENGNDSLOPE

VCC DRAIN

Load Disconnection

DISC FB

STCS05/1/2/A

Input Voltage

PWM

ENGNDSLOPE

VCC DRAIN

Load Disconnection

DISC FB

STCS05/1/2/A

Input Voltage

PWM

ENGNDSLOPE

VCC DRAIN

Load Disconnection

DISC FB

STCS05/1/2/A

ST Solution: STEVAL ILL014V1


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Functionalities: Linear topology Input voltage (VIN): 4.5V to 40V Less than 0.5V voltage overhead Up to 1.5A output current Selectable PWM dimming (internal circuit/ ext input)

Shutdown pin Open LED failure detection


Key Products:

STCS1APUR

BAT46ZFILM

TS3702IPT

L78L05ABUTR

Typical Applications: Advertising kiosk Backlight

Automotive interior and exterior lighting Emergency vehicle warning lights Small appliances lighting General lighting

Purpose & Positioning: To demonstrate the operation of the

STCS1A constant current LED driver To provide a LED driver for automotiveand industrial applications ensuringconstant brightness and extended LEDlifetime

Constant current controller for high brightness LEDsbased on STCS1A

Constant current controller for high brightness LEDsbased on STCS1A

Driving LEDs usign DC-DC converters:


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Driving LEDs usign DC DC converters:Evaluation Boards Summary

AN2333White LED Controller in

Boost topologyup to 20mA3V to 5.5VSTEVAL-TLL001V1STLD40D

UM0677Buck synchronous LED Driverfor high current LED based on

L6726A + MOSfets1A / 1.5A / 2.8A8V to 18VSTEVAL-ILL023V1L6726A

AN2928Constant current Inverse Buck

LED driver350mA48VEVL6562A-LEDL6562A

AN2810LEDs Driver with Boost

Converter for LCD PanelsBacklight

60mA

per channel4.5V to 32VSTEVAL-ILL021V1LED7707

AN1941Cree LED Flashlight with

L6920D350mA1V to 3VSTEVAL-IILL008V1L6920D

AN2129High Intensity LED Dimming

Driver based on L6902350mA8V to 30VSTEVAL -ILL010V1L6902

4.5V to 32V

4.5V to 40V

12Vac

12V to 24V dc

Vin

LEDs Driver with BoostConverter for LCD Panels

Backlight

High Brightness Linear LEDDriver based on STC1A

High Intensity LED driver forMR-16 format based on

L5973D

Comments

AN280920mAper channel

STEVAL-ILL020V1LED7706

UM0422up to 1.5ASTEVAL-ILL014V1STCS1A

AN25591ASTEVAL-ILL007V1L5973D

Part Number ANIoutmaxOrder Code

B k C t LED D i S


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Buck Converters LED Driver Summary

Buck Boost Converters LED Driver Summary


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Buck- Boost Converters LED Driver Summary


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Linear Current Regulators Summary


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Linear Current Regulators Summary

Linear Current Regulators

Contents


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Contents







LED Display typical architecture


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MAINPROCESSOR

ModularConcept

SMPS

Modular solution to fit different screen sizes

LED Display typical architecture

Image Position

adjustment (MEMS)

Data Bus

Flat Ribbon cable

MCU &LVDS

Interface

LED-PCB

LED DriversTemp. Sensor

LED Display Panel: Cluster Architecture


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LED Display Panel: Cluster Architecture

SingleCluster-256RGBLEDs

MAIN

PROCESSORSingle Cluster: 1 MCU, multiple LED Drivers in cascade

More Clusters in Cascade..

MCU LED Driver

SPIControl Panel

Mode

Brightness

Speed

RGB LED ConfigurationLED Block

TemperatureSensor

Circuit Block

SPI SPILEDDriver

OE-

R/G/B L

EDDriver

DM

LE

5v

3.3v

Typical Cluster Architecture Example


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Single cluster combines 4 blocks of 8x8 LEDs Single cluster includes 32 LED Drivers (STP24DP05), 1 MCU (STM32) and 1 temperature Sensor Supply section is based on 3.3V- 600mA LVDO powering both STP24DP05 and MCU.

Module top view

Cluster

Typical Cluster Architecture Example

Driving Concept for RGB LEDs


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Driving Concept for RGB LEDs

How to drive LEDs arrays


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y

Serial Configuration: cascaded driversare used. The data is sent through all LEDdrivers via the SPI and then latched to theoutputs.Advantage: current in each channel is

regulated by software PWM modulation, whichmeans color control of each RGB LED.Disadvantage: lower PWM resolution forhigh LED count, as the data takes time to reachall drivers.

Parallel Configuration: mainly usedwhen high light intensity with many LEDs of thesame color is required.Advantage: simpler method and better PWMresolution, because of faster data transferamong the drivers.

Disadvantage: it increases the number of I/Oson microcontroller in case of RGB applications

Note: It is possible to mix serial and parallelconfigurations to provide different colors depthachieving higher brightness.

LEDs Brightness & Color control by software


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g y

Brightness Control: Limited by PWM resolution and

processing data capability of themicrocontroller or FPGA

It is recommended to select a PWMdimming frequency above 150 Hz to

avoid visible flickering.

Color Control: Depends on three fundamental color

components: Red, Green and Blue. TheRGB components are used to get thedesiderate colors according to the imagedata processing and the white point at

different color temperatures. Color and temperature sensors aregenerally used.

Color GamutColor Gamut

White Point Area

Power Logic LED Driver


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g

Drives multiple low power LEDs used in applications such as signage and matrix display.

Constant current controlin a single chip solution is allowed. Minimum BOM required: one resistorsets the preferred maximum current for all outputs.

Innovative feature of this family are the clockand data re-synchronization useful when at least twodevices are cascaded.

Features such as high channel to channel precision, LED error-detection, auto power-savingand Symmetrical Turn-ON and Turn OFF are integrated into the newest products of the family.

SPI

Interface

Serial In

Latch

Clock

Rext

PowerMOS

PowerMOS

Next LED driverin cascade

Constant

current

Serial Out

Out EN

Cascaded Power Logic devices


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SDI

STP16CP05

SDO

STP16CP05

SDI SDO

STP16CP05

REXT REXT REXT

SDOSDI

LED1 -----------> LED 16

V-LED

Micro

OE

LE

SDI = Serial Data In

Cascaded LED drivers, typical circuit diagram

SDO = Serial Data Out

LE = Latch Enable

OE = Output Enable Pin

1 or 0

LED17 ------> LED 32 LEDn ------> LEDn +16

STP16CPxxNew Constant current P/Ns expand features offering


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New Constant current P/Ns expand features offering

Keep existing Pinout without PCB re-layout

STP16CPCSymmetrical Turn-ON and Turn-OFF

As EMI and inrush current are reduced it suits applications requiring slower Turn-ON and Turn-OFF

times .

Status: Mass Production

STP16CPP/SExcellent accuracy even at low current level.

Latest LED technology has dramatically increased the brightness while lowering the flowing current .

The STP16CPP05 is the best choice to drive LEDs from 3mA to 40mA.

Typical current accuracy +/- 2% among all channels.

/S Version with Auto Power Shutdown - eng sample

STP16DP/P/SExcellent accuracy even at low current level in addition to LED error detection and

Auto Power Saving.Status: Sample Available Pre-production



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Functionalities: Two STP24DP05 with 16 RGB LEDs. STM32 MCU using a cost effective internal HSoscillator. JTAG interface for MCU firmware change/update. Mini USB connector for interconnection with PC GUI Test point to simplify electrical evaluation. Buttons and a knob to control the board.

Error and Over-Temperature Flag for each LEDdriver. LED failure (Open and short) simulation

Input voltage range 7.5V - 18V.

Key Products:

STP24DP05BTR

STM32F103C6T6

ST1S10PUR

LD3985M33R

USBUF01P6

Typical Applications: LED Diplay

Scoreboards LCD Backlighting Traffic diplay and Road Signs

Purpose & Positioning: An inexpensive and accurate current

control for low power RGB LEDs to beused in full color display application . To provide a platform to test andevaluate STMicroelectronics power logicLED driver STP24DP05

RGB LED Array based on STP24DP05 and STM32F103C6RGB LED Array based on STP24DP05 and STM32F103C6

Power Logic Evaluation Boards Summary


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5V, 0.5A3.5V-5V, 3A

UM DRAFT

- Animated Text

- Adjustable Blinking Speed- GPS Interface

- audio output for playback of theprerecorded .wav files

Mother/slave board for LEDdisplay based on STM32.

16 x 32 LED matrix displayunit

STEVAL-ILL024V1

STEVAL-ILL025V1STP16DP05

StandardSupply

Connector

AN2415

AN2478

- Adjustable Brightness

- Adjustable Blinking Speed

- Animated Text

- Error Detection Feature

40 LEDs DiagnosticReference Board Using

OSRAM Blue LEDsSTEVAL-ILL002V3STP08DP05

StandardSupply

ConnectorUM0574


-JTAG interface for C firmwarechange/update

-Mini USB connector for PC GUIconnection


16 RGB LED Array based onSTP24DP05 andSTM32F103C6


RGB LED Reference Board

OSTAR Projection ModuleGolden Dragon LEDs

40 LEDs DiagnosticReference Board Using

Vishay Green LEDs

32 LEDs Array ReferenceBoard

Description

AN2531

AN2415

AN2478

AN2241

ApplicationNotes

Standard

SupplyConnector



- Animated Text

- PowerLED Driving

STEVAL-ILL009V3

STEVAL-ILL009V4STEVAL-ILL009V5

STP04CM05

StandardSupply

Connector



- Animated Text



StandardSupply

Connector



- Animated Text

STEVAL-ILL003V2STP16CP05

STP16CPS05

Part NumberPowerSupply

FeatureOrder Code

Power Logic LED Driver portfolio


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To control LEDs status in road signsFast Ton/Toff Response with LED ErrorDetection

5-100mA

3 - 5.5VSTP08/16DP058/16 Channel

Inexpensive Led Driver solution for H.B. LEDsLow side driver Fast Ton/Toff Response100/250mA5.VSTPIC6D5958 Channel

Suitable soluiton for middle-end video display(RGB)

8CHX3 indipendent groups driver, full LEDerror Detection

5-80mA3.3-5.5VSTP24DP0524 Channel

For High End Display, footprint compatible withbasic STP16xx series

12/16 bit PWM control, Full LED Error Detection

Gain current adjust, advanced thermalmanagement

5-80mA3.3-5.5VSTP1612PW0516 Channel

Reduces switching inrush current and ghost

effect

Symmetrical Ton/off (100nS) ,5-

100mA

3.3-5.5VSTP16CPC0516 Channel

3.3-5.5V

3.3-5.5V

3.3-5.5V

3.3-5.5V

3.3-5.5V

3.3-5.5V

35.5V

VDD

3-40mA

3-40mA

3-40mA

3-40mA

5-100mA

5-100mA

80-400mA

Io

High accuracy ~ 1% at 3mALow current LED driverSTP16CPP0516 Channel

Auto Power shutdown, wake up does not needext.signal

Auto Power savingSTP16CPPS0516 Channel

To control LEDs status in road signsLow current Full LED Error detection,STP16DPP0516 Channel

Significant power savings for Green application+ LED Status control

Low current ,Full Error Detection, Power-Saving

STP16DPPS0516 Channel

Significant power savings for Green applicationAuto Power SavingSTP16CPS0516 Channel

STP08/16CP05

STP04CM05

P/N

Constant current Fast Ton/Toff Response

Integrated solution 4 High current channels

Key Features

Possibility to increase video display frame rate8/16 Channel

Best solution to supply high power LEDs (RGGB)4 Channel

Key AdvantageN.Channel

EXISTING PRODUCTNEW PRODUCT

STP1612PW05: Low Voltage 16-channel LED Driver withGain control , PWM and LED Failure Detection


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Key Features16-channel 3-to-60mA Constant Current

12/16-bit Grayscale PWM Control

Selectable enhanced PWM for ghost effect reduction

8-bit GAIN control with two selectable ranges for global

LED brightness adjustment

Full Output LED Error Detection

Programmable Progressive output delay

30MHz Clock Frequency

Timeout alert if clock signal is missing

ESD protection: 2.5kV HBM, 200VMM

PackageSTP1612PW05MTR (SO-24)STP1612PW05TTR (TSSOP-24)STP1612PW05XTTR (HTSSOP-24)

ApplicationVideo display LED panels, RGB backlighting

MCU

STP1612PW05

1 2 15 16SPIControl

Mode

Brightness

Speed

More Drivers in Cascade

RGB LED ConfigurationLED Block3.3v

TemperatureSensor

Circuit Block

SPI SPI

PW

M

Clk

STP1612PW05

OE

LE

5v

STP1612PW05

Control Panel

Pre-Production

Contents


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LED Backlighting: Introduction


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LED backlight dominates the smaller LCDdisplay market

Cell Phones, GPS, PDA, etc

Larger display have traditionally used ColdCathode Fluorescent Lamps (CCFLs).Compared to CCFL, LED allows:

Thinner backlight design

Advanced backlight architectures

LEDs now are penetrating larger LCDmodules

Notebooks have largest adoption

today-exceed 30% in 2009 Monitor an TVs are emerging markets

LED backlighting driver challenges: Current matching


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To maintain backlight uniformity, all LEDs must have the same brightness LED light is controlled by current, not voltage

Therefore current needs to be matched among LEDs

The current matching target required by LCD markers is 1%

Affected by LED forward voltage spread (10-15%)

Assume the LEDs have a VF range of 3.0V to 3.6V (Typ. 3.3V) and we want 20mA:

Vx Vx

5V 5V 5V 5V 5V 5V

R= (5V-3.3V)/20mA = 85ILED1 = (5V-3.0V)/ 85 = 24mAILED2 = (5V-3.6V)/ 85 = 16mA

Ideal Current Source Perfect matching

Real Implementation

Low cost Poor matching Not suitable for backlight

Active circuit maintains Vf voltage

difference drop across the transistor LED Current is set by Vx/R Best Current matching(1% to 2%) Suitable for backlight LED driver

Each backlight consist of many LEDs 3 to 1000+ depending on the LCD panel size

LED backlighting driver challenges: LEDs Connections


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LEDs can be connected in series and parallel

Series Perfect current matching High voltage LED Driver are moreexpensive Inefficient for high step-up ratio

Parallel Requires current matching circuit Allows using lower voltage drivers Multichannels approach increases the cost

Vs

Vs

A series-parallel combination can be also usedVs

Other LED driving considerations


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VF spread among the LEDs increases the power dissipation/heating White LEDs have a typical VF between 3V to 3.6V

For instance a string of 12 LEDs has a total VF value between 36V to 43.2V

Binning is used to reduce the VF variation

A linear driver needs to absorb the voltage variation (VVAR)

Drivers require an overhead voltage (Vmin) to properly control the current Keeping the overhead voltage low minimizes power dissipation

ST products requires ~ 400mV (typ.) to regulate 50mA.

PDISS= ((N-1) x ILED x (Vmin + VVAR)) + ILED x Vmin

Emitted LEDs light wavelength depends on the current intensity

PWM dimming technique allows changing the brightness without color-shift

Analog dimming can be used to improve the dynamic range (contrast ratio) at low brightness Human eye is less sensitive to low intensity color

To tune RGB LEDs wavelength, current must be independently controlled.

VVAR +Vmin


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Typical LCD display block diagram


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Row

driver

LCDBias

IC

DigitalControl

IC

DigitalControl

IC

Backlight Driver

Backlight Module

Row

driver

Column DriverColumn Driver Column Driver

Power

Video

Power

LCD backlighting for notebook and mid-size display


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White LEDs are used ranging from~ 20mA to ~50mA.

The number of LEDs depends onthe size of the LCD panel and thekind of final application.

The standard displays sizes usinga single driver solution are:

7 = 10 to 16 LEDs

12 = ~ 40 LEDs

14.1 = ~ 54 LEDs

15.4 = ~ 60 LEDs

Usually the driver is powered from12V or 5V bus rail.

In notebooks the input voltagerange is 7V to 20V, varying fromthe battery or the AC adapter.

For other portable devices thedriver is powered by a single cellLi-Ion battery.

STLA0220mA Boost LED Driver for Backlight


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Main Characteristics: Boost DC/DC Converter Synchronous Rectification Drives up to 6 LEDs at 20maA max Output power capability up to 500mW

Input Voltage Range 2.5V To 12V Output Current Control 2.3 Mhz Fixed Frequency PWM Input Brightness Control with

300:1 Dimming Range

350mA Integrated Switch OVP & OTP Less than 1A Stand-by Current Internal Soft Start Package DFN 2x2 6L

Main Application: Small LCD Display Backlight (7) Keyboard Backlight

E.S. Available

VIN

L

CIN

STLA02 R

FB

EN/PWM

VIN

LX

VOUT

FB

GND ILED

VIN

L

CIN

STLA02 R

FB

EN/PWM

VIN

LX

VOUT

FB

GND ILED

Input voltageOutput voltage:

Input voltageOutput voltage:

LED770x: WLEDs Backlight Driver for medium/largeLCD panels (MNT & TV)


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BOOST SECTION 4.5V to 36V Input Voltage range

Internal Power-MOSFET

Up to 93% Efficiency

Up to 36V Output Voltage

200kHz to 1MHz Switching Frequency

Programmable Soft-Start, OVP and OCP

External sync for multi-device application

BACKLIGHT DRIVER SECTION

Six ROWs capable of driving multiple LEDs in series(e.g. up to ten WLEDs per ROW)

LED7706: up to 30mA Programmable Output Currentper ROW

LED7707: up to 85mA Programmable Output Currentper ROW

LED7707: ROWs in parallel to drive up to 510mA LEDs

1.5% Current Matching between ROWs

Shorted and Open LED Fault Detection

PWM Dimming (LED7706: 500ns minimum dimming ONtime; LED7707:10us minimum dimming ON time)

TARGETED APPLICATIONS Consumer: Mid to large size LCD (TV & MNT)

Automotive: navigation displays and dashboards

Industrial: lighting, displays

FAULT

ROWSCTRLMODE

BOOSTCTRL

LDO

DIM RILIM

range: 4.5V to

Vout

FAULTMNGMT

Output voltage:

up to 36V

EN

PWMdimming

Six rows, up to10 WLEDs each

Up to 85mAprogrammableoutput current

Shorted LEDand open rowmanagement

Internal

+5V LDO

InternalPower-MOS

FAULT

ROWSCTRLMODE

BOOSTCTRL

LDO

DIM RILIM

range: 4.5V to

Vout

FAULTMNGMT

Output voltage:

up to 36V

EN

PWMdimming

Six rows, up to10 WLEDs each

Up to 85mAprogrammableoutput current

Shorted LEDand open rowmanagement

Internal

+5V LDO

InternalPower-MOS

STEVAL-ILL020V1

STEVAL-ILL021V1

V t 36VL

LED770x: Application Schematic


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ROW1

ROW2

ROW3

ROW4

ROW5

ROW6

LDO5

BILIM

RILIM

SS

SGND

SLOPE

VIN L

X

OVSEL

SWF

AVCC

FAULT

EN

SYNC

MODE

PGND

DIM

VIN= 4.5V to VOUT VOUT= up to 36V

COMP

+5V

Up to 10 WLEDs per row

Enable

Dimming

Fault

LED770x

L

MLCC

Sync Output

Faults Management Selection

OVP selection

Switching Frequency selection

Slope Compensation

Rows current select.

Internal MOS OCP


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Monitor and TV LED Backlighting


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Both white and RGB LEDs are used Low (50mA) or high power (350mA) can

be used

The number of LEDs depends on thepanel size and the LED type:

Up to 2000-4000 low power LEDs A few hundreds for high power LEDs

Require multiple drivers per system

Power supply is typically 24V

Local dimming improves LCD technology

drawbacks: Contrast ratio

Power Consumption

Backlight is adjusted according to thepicture content and the area of the screen

Scanned backlight improves motion blureffect and it can be combined with localdimming


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Documents

LED Seminar (Elko - Julio 2012)