Introducing LED Backlighting Solutions - NXP … Panel LED Solution ... LED backlights dominate the...

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Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009.

AC103Introducing LED Backlighting Solutions

June 14 - 16, 2009

Michael JenningsMarket Segment Manager – Display Products

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2Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2009.

Contents

►Target Applications►LED Backlighting►LED Advantages►Technical Challenges►Advanced Architectures►Notebook/Medium Panel LED Solution►Large Screen LED Solution►Future Products ►Summary

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Target Applications

LCD-TV – 22%

Notebook – 27%

Monitor – 39%

Automotive – 2% Picture Frame – 2%

Industrial – 2%

Portable DVD – 5%

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LED Backlighting Introduction

►LED backlights dominate the smaller LCD display market• Cell phone, GPS, PDA

►Larger display have traditionally used Cold Cathode Fluorescent Lamps (CCFLs)

►LEDs now penetrating larger LCD modules• Notebooks have largest adoption today• Monitor and TVs are emerging market

CCFL LED

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LED Backlight Classification

► The LEDs used in backlighting are characterized in two major ways

1. Current capability• Standard LED – drive current < 50mA• High current LED – drive current 50 – 150 mA• High power LED – drive current 150 – 1000mA+

2. Color• White LEDs• Red, Green and Blue LEDs

Combined to make white

► LED forward voltage depends on color• Red ~ 2V, Green ~ 3.5V, Blue/White ~3.5 – 4V

Philips Luxeon K2High Power LED

Standard LED

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The LED Advantage

►LEDs have many advantages compared to CCFL• Point source characteristics enable more flexible backlight architectures

Enables thinner backlight designsEnables advanced backlight architectures

• Higher efficacy (more light at a give power) – White LEDs only today• Longer lifetime (50,000 hrs vs. ~20,000 hrs.)• Dimmable – accurate with infinite steps• Low voltage drivers reduces complexity• Environmentally friendly (CCFLs contain mercury)• Rugged – CCFLs are glass and can break easily• Reduced IR emission – no interference with remote devices• RGB specific advantages

Wider color gamutTunable white point

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LED Driver Challenges – LED Connection

► Each backlight consists of many LEDs – 3 to 1000+ depending on display size

► LEDs can be connected in series or parallel

SeriesPerfect current matchingHigh voltage drivers are more expensiveInefficient for high step up ratio

ParallelNeeds current matching circuits – less accurateEnables lower voltage driversNeeds many channels = expensive

Series/ ParallelCompromise between high voltage and number of driversBest cost/ performance ratioMost common approach for >8 LEDs

25V

17V

5V

= 4S4P

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LED Driver Challenges – Current Driver

► To maintain backlight uniformity, all LEDs must be the same brightness• For LEDs, light output is dependent on current, not voltage• Therefore current needs to be matched

Target for TV = ±1% matching, Target for monitors and notebooks = ±2%• Complicated by the fact that LED forward voltages (VF) vary by ±10-15%

► Assume the LEDs have a VF range of 3.0V to 3.6V (Mean = 3.3V) and we want 20mA

Resistor current setting Ideal current source Real world implementationR = (5 – 3.3)/20mA = 85Ω = perfect matching Active circuit maintains voltage across currentILED1 = (5 – 3.0)/85 = 24mA setting transistor - VxILED2 = (5 – 3.6)/85 = 16mA VF voltage difference drop across transistor> Low cost LED current set by Vx/R> Poor matching ±20% Matching set by Vx accuracy> Not suitable for backlight > Suitable for backlight driver

> Freescale has best in class current matching±1% to ±2%

5V 5V5V

VxR

5V 5V 5V

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5V 5V5V

VxR

5V 5V 5V

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LED Driver Challenges – Power Dissipation

►VF variation between LEDs increases power dissipation/ heating• Typical white LED spec’d with VF = 3.0V min, 3.6V max.

Binning can be used to sort LEDs and reduce this variation• For a string of 12 LEDs, this means VF(total) = 36V to 43.2V• In reality, statistical distribution may give 2V - 3V variation• The linear drivers have to absorb this voltage difference (VVAR)• In addition, there is a minimum voltage in the drivers needed

for the current driver (VMIN)Reducing this to a minimum, helps keep power dissipation downHowever there is a trade off with current accuracyFreescale products typically around 500mV

• PDiss = ((n – 1) x ILED x (VMIN + VVAR)) + ILED x VMIN

• e.g. For 8 channels, driving 50mA LEDs with average variation of 3V• PDiss = ((8 -1) x 50.10-3 x (0.5 + 3)) + 50.10-3 x 0.5 = 1.08W

►Dynamic Headroom Control (DHC)• To reduce power dissipation, the string voltage (VS) should be kept to a minimum• As LED voltage is unknown, fixed output voltage must assume worst case (43.2V)• DHC measures the voltage connected to the LED driver and adjusts the output voltage

(VS) to the minimum capable of driving the LEDs – 500mV for FSL drivers• Delivers minimum possible dissipation/ highest efficiency for LED driver

VVAR + VMIN

VS

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►Freescale products use linear current drivers►Alternatively can use switching driver

Linear Driver Switching Driver

Single DC:DC Separate DC:DC per stringLinear driver absorbs string difference Switcher absorbs string difference= higher power dissipation = higher efficiencyFewer expensive external components Requires separate inductor+capacitors/ string= lower cost = higher cost= smaller footprint = large PCB area

LED Drivers – Linear vs. Switching

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LED Placement

►Edge lit backlight

• LEDs along edge of display• Generally used in smaller panels

Now in TV’s up to 40”• Enables super thin backlight

<2mm thick for notebook• Uniformity worst than direct

backlightEspecially for larger displays

►Direct backlight

• LED array behind LCD• Used in larger panels

30”+• Enables advanced architectures

Scanning and local dimming• Good uniformity

Backlight Driver Backlight Driver Backlight Driver Backlight Driver

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Advanced LED Backlight Architectures

►Advanced LED backlight architectures are being used to overcome drawbacks of the LCD technology

►One such drawback is contrast ratio

►A second is power consumption

►Local dimming improves both• Backlight is divided in to a number of zones• The backlight is then adjusted depending on the

picture contentContrast ratio improvements to >500,000:1 possible

– Standard LCD ~ 5000:1Reduces power dissipation up to 60%

– The backlight consumes 30%+ of power in LCD-TVs

Without With

Local Dimming

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Advanced LED Backlight Architectures

►Another problem with LCD is motion blur

►This can be improved using scanned backlights• Backlight is divided into rows • Light is scanned down the display at frame rate• One or more rows can be illuminated at a time• Eye tricked in to seeing faster refresh• This removes the blur effect

►Often combined with local dimming

With Scan

Without Scan

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The Freescale Advantage

►Experience• Assembled expert team with many years LED driver experience• System group engaged with major LED backlight vendors for complete solution

approachConvert LCD panels to LED backlightUnderstand all aspect of backlight designDeep understanding of LED design challenges

►Technology• Freescale SMARTMOS™ technology• Enables integration of high density control

logic, with integrated power device andaccurate analog control circuits

►Proven Capability• Our existing custom products are the highest performing LED drivers on the

market• Standard products offer innovative features and differentiated performance to

stand out from the competition

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Notebook and Mid-size Display LED Drivers

►Typically use white, standard LEDs (20 to 30mA)

►Edge-lit is used in almost all these displays

►The number of standard white LEDs varies depending on the application• 10 – 100 LEDs will be used depending on screen size

7” = 10-16 LEDs12” = ~40 LEDs14.1” = ~54 LEDs 15.4” = ~60 LEDs

• Typical applications have a single driver

►Drivers are powered from either• Internal 5V or 12V• Direct from battery

7 to 20V in notebooks

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MC34845 Introduction

►MC34845 is a 6-channel, fully integrated white LED driver• Target panel sizes from 10” to 17”• Can drive max.96 LEDs from a single device (16S6P)

Single chip solution in many applications

►Targeted Applications

Industrial/Instrumentation Picture Frame Portable DVD MedicalNotebook

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MC34845 Advantages

►Advantages• 60V boost output capability supplies more LEDs in series

Drives 96 LEDs from single device using standard 6-pin interconnect• Small BOM to minimize footprint and cost

Includes integrated boost FET• PWM up to 25kHz to remove audible noise concerns• Advanced dynamic headroom control to reduce power dissipation in IC

and improve backlight efficiency• High speed drivers provides for improved PWM range even at 25kHz

Minimum input pulse down to 200nsLinear range from 0.4% to 100%

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BoostController

Regulators

6 channel30mAcurrentdriver

VIN

EN

SW

I0

I1

I2

OCP/OTP/UVLO

I3

PWM

DHC / Fault Detector

COMPOVP

I4

I5

GNDA

VDC1 SW

VDC2

PGND

OVP

ISETDGND

VOUT

WAKE

SLOPE

MC34845 Notebook LED Driver

►Features• Input voltage range 5V to 21V• 2.0A Integrated boost

600kHz or 1.2MHz• Output Voltage up to 60V• 6 channel LED driver

Up to 30mA LED current±2% current matching

• Direct PWM input controlPWM frequency up to 100kHz30,000:1 dimming range200ns minimum pulse

• Dynamic Headroom control• LED open/short protection• User programmable OVP • OTP, OCP, UVLO fault detection• Shutdown to <1μA • 24-Ld QFN 4mm x 4mm x 0.65mm package

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Monitor and TV LED Drivers

►For monitors and TVs both white and RGB LEDs are used

►Can use all types of LED from standard to high power (50mA to 350mA)

►Edge-lit is most popular today with direct backlight in high end models only

►The number of LEDs depends on the size of panel, and the type ofLED

• Can use 2000 – 4000 standard LEDs• For high power LEDs, a few hundred units are used• Requires multiple drivers per system

►Power typically comes from a 24V supply

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►MC34844 is a 10-channel, fully integrated white LED driver

• Target panel sizes from 14” to 27”• Can drive max.160 LEDs from a single device

(16S10P)Single chip solution in many applications

►Targeted Applications 24” white LED monitor driven using single MC34844

Industrial/Instrumentation MedicalMonitors TVs

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MC34844 Advantages

►Advantages• 10-channel, 60V drivers support up to 160 LEDs

One chip supports monitors up to 24”• Small BOM to minimize footprint and cost

Includes integrated boost FET• PWM up to 25kHz to remove audible noise concerns• PWM synchronizing capability to remove visual noise artifacts• Advanced dynamic headroom control to reduce power dissipation in IC

and improve backlight efficiency• High speed drivers provides for improved PWM range even at 25kHz

Minimum pulse down to 200nsLinear range from 0.3% to 100%

• Supports I2C/SM-Bus/PWM control inputs• Temperature/optical sensor inputs

Closed loop control for improved uniformity over lifetime/tempAmbient backlight control for improved battery life

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MC34844 White LED Driver

►Features• Input voltage of 7V to 28V• 3.0A Integrated boost

150kHz to 1.2MHz• Output Voltage up to 60V• 10 channel LED driver

Up to 50mA LED current±2% current matching8-bit programmable for each channel

• Internal PWM generator100Hz to 25kHz8-bit resolution

• PWM synchronizing capability100Hz to 25kHz

• I2C/ SM-Bus interface• Dynamic headroom control• Temperature/optical compensation loops• LED short detection• User programmable OVP • OTP/OCP/UVLO lockout• 32-Ld QFN 5mm x 5mm x 1mm package

Boost Controller

REG 1

10 channel 50mA current mirror

PWM Generator

I2C/ SM-Bus interface

VIN

SCK

GND

EN

SW

I0

I1

I2

ISET

OCP/OTP/UVLO

I3

PWM

Temp/Opto loop control

PIN

NIN

Clock/ PLL CK

V sense

COMP

OVP

M/~S FAIL

I4

I5

PGND

SDA

A0/SEN

VDC1

SW

I7

I8

I9

I6

Current DAC

VOUT

REG 2 VDC2

PGND

GND

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Road Map

2008 2009 2010

60”

20”

30”

40”

50”

10”Not

eboo

k

Mon

itor

Net

book

Tele

visi

on

MC348456-channel

Driver + DC:DC

MC3484410-channel

Driver + DC:DC

Local dimming direct backlightchipset solution

MC348466-channel

Driver + DC:DC

(TBD)4-channel

Driver + DC:DC

Mul

tiple

devi

ces

Edge-litLED Driver

Next gen. Mon.Adv 8-channel

Driver + DC:DC

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►MC34846 is a 6-channel, advanced functionality white LED driver• Target panel sizes from 10” to 17”• Integrates advanced features for audible/visual noise reduction

►Targeted Applications

Industrial/Instrumentation Picture Frame Portable DVD MedicalNotebook

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MC34846 Advantages

►Advantages• 52V boost output capability supplies more LEDs in series

Drives 84 LEDs from single device using standard 6-pin interconnect• Small BOM to minimize footprint and cost

Includes integrated boost FET• High speed PWM output up to 25kHz • Reduced audible noise• Simplified DC:DC design• Improved efficiency

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MC34846 Advanced White LED Driver

►Features• Input voltage range 5V to 24V• 2.0A Integrated boost FET

300kHz to 1.5MHz• Output Voltage up to 52V• 6 channel LED driver

Up to 30mA LED current±1.5% tolerance

• Internal PWM generator100Hz to 25kHz10-bit resolution = 1000:1 dimming range

• Direct PWM control mode100Hz to 75kHz200ns minimum pulse30,000:1 dimming range

• Dynamic Headroom control• User programmable OVP• LED open/short detection• OTP, OCP, UVLO fault detection• Shutdown to <1μA• 20-Ld QFN 4mm x 4mm x 0.65mm package

MODE

BoostController

Regulators

6 channel30mAcurrentdriver

PWM Generator

VIN

PWM

SW

I0

I1

I2

OCP/OTP/UVLO

I3

DHC

OVP1

I4

I5

GNDAPWM_SET

VDC1

PGND

ISET

LogicControl

OVP

5V to 24V

EN

SW

F_BOOST

P_RST

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LED Backlight Controllers

►For RGB color control, simple 8-bit MCU is sufficient• Freescale solution based on 68HC9S08AW60• Patented color control system architecture

LCD TV main LCD TV main Processor InterfaceProcessor Interface

Color sensor inputsColor sensor inputs

FPGAFPGABoard InterfaceBoard Interface

User User Control InterfaceControl Interface

SystemSystemMonitoringMonitoring

UARTUART

BDMBDMinterfaceinterface

Package : 44/64LQFPPackage : 44/64LQFP

VSSVSS VDDVDD VSSaVSSa VDDaVDDa

60K FlashLCD TV main LCD TV main Processor InterfaceProcessor Interface

Color sensor inputsColor sensor inputs

FPGAFPGABoard InterfaceBoard Interface

User User Control InterfaceControl Interface

SystemSystemMonitoringMonitoring

UARTUART

BDMBDMinterfaceinterface

Package : 44/64LQFPPackage : 44/64LQFP

VSSVSS VDDVDD VSSaVSSa VDDaVDDa

60K Flash

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Freescale Color Management Control System

Auto calibration is possible in the manufacturing stage !Auto calibration is possible in the manufacturing stage !

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Small Panel Solutions

►White LEDs dominate small panel backlighting• Cell phones, DSC, smart phone, PDA, MID, GPS…

►Historically have used separate LED driver►Majority applications now moving to integrated solutions►Freescale supports this market through integrated solutions only

Future IC

PMIC for portable productsIntegrates LED driver

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Summary

►Freescale highly focused on LED backlight market

►Leverage system expertise and Freescale advanced technology to provide differentiated, enabling products

►Freescale products in volume production today

►Future road map to cover all types of LED backlight requirements

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►Thank you for attending this presentation. We’ll now take a few moments to review the audience questions, and then we’ll begin the question and answer session.

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Q&A

Introducing LED Backlighting Solutions - NXP … Panel LED Solution ... LED backlights dominate the...

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