LED Solutions for LCD Backlighting

LED Solutions for LCD Backlighting
ST Position:• #1 in Lighting Segment*• #2 in Power Management**

Systemknow-how

LED DriverICsApplications
flexibilitiy

LEDAppl.

BestPerformance

PowerSavings*STMicroelectronics, Datapoint and Darnell - 2008**iSupply - 2010

ST Expertise:• System Solutions• Technology Integrationand Innovation• Excellent Technical Support

Contents
 LED Solutions for LCD Backlighting LED Array Driver Features/Benefits Error Detection/Diagnostics
 Auto Power Savings/Shutdown PWM Dimming External Synchronization Capability

 System Evaluation Boards and Tools
 LEDs Driver with Boost Converter for LCD Panels
Backlight White LED Controller in Boost topology
 6-row, 30 mA LED driver with Boost

LED Solutions for LCD Backlighting

LCD backlighting
applications: LED TVs
 PC monitors
 Notebooks
 Netbooks
 Mid to Large-sized
LCDs

LED7706/07/08,
STLA02, STLD40/41
PM6600Topology and architecture
flexilbility
 Buck-Boost improved
efficiency
 High side control in Boost
topology for improved
accuracy High Frequency (2MHz)operation with PWM control
 Chip scale packaging
solutions Smallest application area

Lighting Management - BacklightLED Drivers for Backlighting
Part
NumberDrive(# ofLEDs)

Iout(mA)

Vinrange
(V)

Fsw
(MHz)

STLA02620

2.5-182.3

Synchronous, PWM Dimming

STLD401020

3.0-5.5

0.5

Asynchronous, PWM Dimming

STLD4140 (4 stringsof 10)120

3.0-21

1.8

Asynchronous, PWM Dimming

STLD2510 (5 stringsof 2)25

2.3-5.5

2.5

Asynchronous, PWM Dimming

LED770660 (6 stringsof 10)30

4.5-360.2-1

Ext. Sync. Capability, PWMdimming

LED770760 (6 stringsof 10)85

4.5-360.2-1

Ext. Sync. Capability, PWM
dimming

LED7708160 (16strings of 10)85

3.6-36

0.25-1

Ext. Sync. Capability, PWM
dimming

PM660060 (6 stringsof 10)32

4.7-280.2-1Ext. Sync. Capability, PWM
dimming

Notes

STLA02 Boost Converter LED DriverFeatures: Supply Input range 2.5V – 18V
 Synchronous rectification
 Output voltage up to 27V
 Drivers up to 6 LEDs in series
 High side current sensing
 Simple Topology to connect LEDs
 LED current 20mA
 2.3MHz Freq PWM control
 Enable and Dimming current (300:1) withdedicated Pin
 Soft Start Over Temperature and Voltage protections
 Package DNF6 2x2 mm

Application schematic

STLA02

ST advantages:
 High side configuration allows single layer PCB
 Synchronous rectification
 High switching frequency reduces size ofexternal components
 Tiny package DFN2x2

STLA02 EVAL Board
See ST Sales team for availability

STLD40D W-LED Power Supply
w/Evaluation board for Large Display BacklightL=4.7µH

DVBATT

Features: Inductor switcher boost converter
Cin=2.2µF
 Vin range : 3.0Vdc to 5.5Vdc
 High efficiency >80% over wide range of Vin from 3-37V
 Can drive up to 10 white LEDs in series
VIN Output Current capability 20mA
 Enable pin with possibility of PWM dimming control
 OVP and OVT protections with automatic restartEN PFM mode control
 Soft start with adjustable peak current limit Small external inductor
 QFN 3x3 8 leads 1mm Height

Cout=100nF

VOUT

SW

RSET
R SET

STLD40D

N/CFB

GND

R LED

Typical applications:White Led supply for LCD backlight
Mobile phone/smart phonesPDA and organizers
Handheld POS
Digital camera
MP3
Any handsets powered by Li-ion battery

STEVAL-TLL001V1

Part #Evaluation BoardVinIoutmax

Description

App Notes

STLD40D

STEVAL-TLL001V13.0-5.5V20mA

White LED power supply for large display backlight

AN2333

STLD41 – Single Channel WLED DriverWhite LED Power SupplyFeatures:












White LED boost converter
Drives up to 40 LEDs (4 strings of 10 LEDs)
Vin range: 3.0Vdc to 21Vdc
Operating Vout: ~38V
Output Current capability 120mA adjustable bysingle resistor
PWM/PFM Control Mode (1.8 MHz)High efficiency w/2 or 3 Li+ cells
Adjustable peak current
Separate PWM dimming and enable pins
Over voltage and over temperature protections
Soft start
Low shutdown current < 1µA.
Package QFN 3x3-8 leads

ST advantages:

Low cost solution
LED configuration flexibility
Few external components needed

Application schematic

STLD41APPLICATIONS:
Mid-size LCD backlight Tablet Mobile phone
 PDAsSTLD25 - 5 Channel WLED DriverFeatures:
 Operating input voltage from 2.3V
to 5.5V
 + 7.5% LED current accuracy
 Two LEDs in series, 5 channels todrive up to 10 LEDs
 High side current source Up to 125mA of total LEDs current
 90% efficiency at 100mA
 PWM Dimming with automatic
shutdown time window
 2.5MHz switching frequency
 CSP 12 bumps 0.4mm pitch
1.4x1.8mm

Typical Applications: LCD backlight with up to 10 LEDs Cellular phones
 PDAsApplication schematic

STLD25

Using DC-DC Switching Regulators
In Driving LEDs
Monolithic solutions offer high efficiency and compactness, wide input voltage range,high current capability for a variety of applications, and high dimming performancefor superior brightness uniformity.

LED770x

Boost for multi-rows
applications

DC BUS powered applications

Optimized LED driving solution
LED7706 and LED7707
DC-DC
Converter
DC-DC converter

DC-DC
DC-DC

converter
Converter

SerialDC-DC
DC-DC
Converter
converter

ParallelMultiple channel

 simpler architecture brightness uniformity
 high voltage tomanage

 low voltage
 high complexity due tocurrent matching high power dissipation on
current generators

 Typical input bus available  24V
 LEDs to drive  up to 10(e.g. considering 40V technology)

LED770x Trade-off based on: technology availability(rated voltage) efficiency
 LED current regulation

NEED FOR BOOSTCONVERSIONLED7706/7: LED Controllers
MAIN FEATURES
Boost section
 4.5V to 36V Input Voltage range
 Internal +5V LDO
 Internal Power-MOSFET Up to 93% Efficiency
 Up to 36V Output Voltage
 200kHz to 1MHz Switching Frequency
 Fixed FSW Peak Current Mode control
 Programmable Soft-Start Duration
 Programmable OV and OC Protections
 Single Ceramic Output Capacitor
 External sync for multi-device application

Backlight driver section
 Six ROWs capable of driving multiple LEDs inseries (e.g. up to ten WLEDs per ROW)
 Programmable Output Current per ROW

Input voltage
range: 4.5V
to Vout
Internal
Power-MOS

Internal +5V
LDO

Shorted LED
and open row
management
PWMdimming Up to 30mA (LED7706)
 Up to 85mA (LED7707)

 PWM Dimming
 500ns minimum dimming ON time (LED7706)
 10uS minimum dimming ON time (LED7707)

 2% Current Matching between ROWs
 Shorted LED Fault Detection
 Open ROW Fault Detection
 Capability to Disconnect Unused ROWs

LED7706/7

Output voltage:
up to 36V

Six rows, up to 10
WLEDs each
Up to 30mA (LED7706)
85mA (LED7707
programmable outputcurrent

Ideal for:
Backlighting for Medium and Large LCD panels• Monolithic and flexible solution• High efficiency• Superior dimming capability• Complete and flexible fault management

LED7708 LED Controller
MAIN FEATURES
Boost controller section
 3.6V to 36V Input Voltage range
 Adaptive output voltage for high efficiency
 Internal +5V LDO for gate driver supply
 Internal +3.3V LDO for device supply
 High performance external MOSFET driver 250kHz to 1MHz Switching Frequency
 Fixed FSW Peak Current Mode control
 External sync for multi-device application
 Programmable OV and OC Protections
 Over-temp alert and thermal shutdown
Up to 160 White-LEDs

LED array driver section
 4-wire, 30MHz serial interface
 16-channels with 85mA/ch current capability
 Selectable 12/16-bit gray-scale Programmable gray-scale latency
 Grouped or independent channel PWM control
 1.5% max channel-t-channel current matching LED short-circuit and open-channel fault detectionand management Serial data formats: 16x16 bits, 1x256bits or1x192 bits

Ideal for:
Backlighting for LCD TVs
 Advanced local dimming performance Adaptive LEDs voltage regulation
 Flexible solution
 High efficiency
 Superior brightness control
 Complete and smart fault management

LED770x: Adaptive Output Voltage
Minimizing the power consumption
Higher power dissipation

Fixed output voltage
VF spread

Adaptive output voltage
Output voltage
depends on the active
LED string with highestVF

Minimization of thepower dissipation on thecurrent generators

Example• VIN = 12V• 6 strings of 8 LEDs
• VF,LED = 3.5 0.2V
• fSW = 600kHz• IROW = 75mA

5*N*VFmin
5*N*V
FMIN

N*VFMAX
N*V
FMAXILEDILED
BOOST
BOOST

LED7707
LED7707η = 84.2% (fixed VOUT approach)η = 87.3%* (adaptive V approach)
15

OUT

0.7V

*0.5% lower every 100mV of increase of thevoltage across the master generators

LED770x: Boost topology
VIN= 4.5V to 36V

VOUT= up to 36V

Wide input
voltage range
+5V

OVP

LDO

High
efficiency

RRILIM
C L
T O
R GL ICFault
EnableCURRGEN(LED7707@VOUT=34V, IOUT=350mA)

95%

ηVREF

LED770x
PWM Dimming

Input voltage: 4.5V to 36V
Maximum RMS switch current: 2.5A
Parallelable channels for higher current(LED7707)

Up to 10white LEDs
per row

I LED =KRRRILIM

90%
14V

INPUT VOLTAGE

24V

LED current:
up to 85mA/ch (LED7707)

Channel to channel current mismatch: ±2%
Up to 20kHz PWM dimming (1%-100%, LED7706)

LED Faults & Dimming Waveforms
1) ROW0Opens
2) The output
voltage increases
3) If 95% is crossed,
the faulty ROW isdisconnected1) LED Short
Circuit: the ROW0
Voltage Increases
2) If the 3.4V
threshold is crossed,
the device is turnedoff (MODE=0)

Detecting and Managing Faults in LED7706/7/8

20µs Dimming
On-Time500ns Dimming
On-Time(fDIM=10kHz, DDIM=20%, fSW=630kHz, LED current=20mA)

Managing Dimming Waveforms in LED7706/7/8

LED7706/7 LED Driver Application Examples
Slope Comp OVP selectSlope Comp OVP selectSwitching Freq SelectInternal MOS OCP
Rows current selectSwitching Freq SelectInternal MOS OCP
Rows current selectUp to 10 High
Brightness (510mA)
WLEDs

Up to 10 WLEDs per row
Dimming
Fault
EnableFault Management SelectSync Output

Typical application schematic

660kHz MASTERDimming
Fault
EnableFault Management SelectSync Output

High-Brightness LED driving solution

660kHz Daisy-Chained SLAVESMulti-device applications with external Synchronization18

LED7706/7 LED Driver w/Boost Converter
Evaluation Board Solution
Key Features:
Boost section
 4.5 V to 36 V input voltage range
 Internal power MOSFET Internal +5 V LDO for device supply
 Up to 36 V output voltage
 Constant frequency peak current-mode control
 200/250 kHz to 1 MHz adjustable switchingfrequency (LED7706/7)
 External sync for multi-device application
 Pulse-skip power saving mode at light load
 Programmable soft-start Programmable OVP protection
 Single ceramic output capacitor
 Non-latched thermal shutdown

Typical Applications: LCD monitors & TV Panels
 PDAs Panel Backlight GPS Panel Backlight Emergency Lightning

STEVAL-ILL020V1

STEVAL-ILL021V1

LED driver section
 Six rows with 30/85 mA maximum current
capability (adjustable) LED7706 /7
 Up to 10 white LEDs per row
 Rows disable option
 Less than 500 ns minimum dimming time
(1% minimum dimming duty-cycle at 20 kHz
dimming frequency - LED7706,
 Less than 10 μs minimum dimming time at 1kHz
dimming frequency - LED7707
 2.0% current matching between rows
 LED failure (open and short circuit) detection

Part #Evaluation BoardVin

Ioutmax

Description

App Notes

LED7706

STEVAL-ILL020V1

4.5V to 36V

20mA /chLEDs Driver with Boost Converter

AN2809

LED7707

STEVAL-ILL021V1

4.5V to 36V

60mA/chLEDs Driver with Boost ConverterAN2810

PM6600 LED Driver w/Boost Converterand Evaluation BoardOutput voltage:
up to 36V

Input voltage range:
4.7V to 28VKey features 6 rows with up to 10 LEDs/row (60 LEDs)
 Monolithic solution up to 36V output voltage
 Programmable LED current up to 32 mA at highest precision/
matching accuracy Supports analog and digital dimming Boost Fsw from 200Khz to 1MHz and high efficiency at light load
 Pulse-skip power saving mode at light load
 LED failure (open and short circuit) detection
 Soft-start, programmable OVP protection, thermal shutdown
 Internal power MOSFET, reducing space and application cost
 Ceramic output capacitor supportedPM6600
Internal
PowerMOSENInternal+5V LDO
MODE
FAULT

BOOST
CTRL
LDO
FAULT
MNGMT

DIM RILIM
Shorted LEDsand Open
ROW
management PWM
dimming

Key benefits

ROWS
CTRL

 Covers all mobile PC and netbook screen sizes (8” to 17”)
 Superior brightness uniformity, with tight current matching Longer battery life with energy regulation compliancy (VESA-NEBL)
 Saves BOM cost, supporting MLCC output cap w/default values
 Space-saving monolithic solution in 24-pin QFN4x4Six ROWs, upto 10 WLEDseachUp to 30mA programmable
output current
3.1mm
1.2mm

Typical applications
 Notebook panels, netbooks, and nettops
 Tablet PCs
 Battery/AC adapter supplied equipment

VFQFPN-24 4x4mm2

STEVAL-ISA056V1

Part #Evaluation BoardVin

Ioutmax

Description

PM6600STEVAL-ISA056V1

4.7 - 28V

32mA6-row, 30 mA LED driver with boost

PM6600: Higher Efficiency – up to 93%
 WLEDs board + PM6600 save board space Save Power in whole dimming rangeVin = 12V
10090

FULL LOAD

Efficiency [%]807060fDIM = 500Hz50fDIM = 20kHz

LIGHT LOAD

403020100020406080100

DIM duty cycle [%]VIN=12V, VOUT=34V (6x 10WLEDs 100mV VF Spread), ILED=20mA
Switching Frequency: fSW=630kHz, L=6.8µH

Driving LEDs using DC-DC converters
Evaluation Boards Summary
Part Number
LED7706

Order CodeSTEVAL-ILL020V1

VinIoutmax

Comments

AN

4.5V to 32V

20mA
per channel

LEDs Driver with Boost
Converter for LCD Panels
Backlight

AN2809LEDs Driver with Boost
Converter for LCD PanelsBacklight

AN2810

LED7707

STEVAL-ILL021V1

4.5V to 32V

60mA
per channel

STLD40D

STEVAL-TLL001V1

3V to 5.5V

up to 20mA

White LED Controller in
Boost topology

AN2333

PM6600STEVAL-ISA056V1

4.7 to 48V

32mA

6-row, 30 mA LED driver with
BoostTBD

LED Solutions for LCD Backlighting
on ST.COM
LED Lighting Brochure

LED Application web pages

http://www.st.com/internet/com/segment/4.jsp

http://www.st.com/internet/com/SALES_AND_MARKETING_RESOURCES/
MARKETING_COMMUNICATION/MARKETING_BROCHURE/brlighting.pdfeDesign Studio

www.st.com/edesignstudio

Add LCD Backlighting block diagram here

ST LED Lighting Solutions

For more information, visit:www.st.com > home > support > tools & resources
www.st.com > Backlighting

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