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Advanced LED Backlighting Technology

Justin ZhaoNov 1st, 2008

Including ALS (ambient light sensing), dimming & fading, fun-lighting, etc..

http://www.elecfans.com 电子发烧友 http://bbs.elecfans.com 电子技术论坛

— China Power Technology Forum 2008 —

Backlighting Problem –Power Budget – Smart phone

Display and Backlight are biggest culprit for power now and evenmore so in the future

Why is the display on ?• Texting (SMS) available 99% of

handsets• Navigation (GPS) available in 33%

of handsets by 2012• Games (Enhance Audio) available

in 68% of handsets by 2012• Video/Pictures Taking (Camera &

MMS) available in 83% of handsets by 2012

• Video View (Mobile TV, Enhance Audio) available in 33% of handsets by 2012

• Email available in 86% of handsets by 2012



Solution 1 : Ambient Light Sensing

Using a PhotoDiode to measure the Ambient Light ConditionsLight level is used to Dynamically adjust the backlight light intensity to match the ambient light

Higher Backlight Current in Higher Ambient Light Conditions

Some example SettingsOutdoor 16mA (5-6 LEDS)Office 5mADark 1.5mA



Solution 2 : Image Content Based Adaptive Backlight Control (cABC)

90% of Display Power is taken by BacklightCABC looks at video image data and used PWM to reduce backlight based on content. (Darker Images require less backlighting)Average reduction in power is 30%Gamma Compensation of Image Required

Image Data



Ambient Light Sensor ImplementationsIt is critical to maintaining battery life as backlight + (keypad) usage increases

Method #1 – Manual ☺ Method #2 - ADC

User manually adjusts backlight to level most often used –“office” +must be ok in daylight GPS, Video, Internet = Dangerous, FrustratingHigher IAverage = Less Battery Life

e.g Capella CM3200 Requires Processor polling and ADC (built into processor)Sony Ericsson xxxx, Nokia xxx, xxxx, xxx– Discrete (E.g. Osram SFH3710 Photodiode)



Ambient Light Sensing

Method #3 – Dual Sense I2C Method #4 – Angelfish etc.

TAOS TSL2563I2C Interface., 2 x 16-bit ADC, INT represents changeRequires Processor PollingNokia xxxx, xxxx, xxxxApple xxxxx

ADP5520, ADP5501, ADP8860Requires no processor polling



Ambient Light based Backlight control –ADI Implementation

Mux

L1

L2

CMP

CMP

0 – 400uA

Brightness

0 uA (0Lux)

400 uA (1k Lux)L1

L2

Dark Office Outdoor

I2C Registers

L1, L2 Programmable Trip Points

Ambient Light

Bac

klig

ht

L1

L2

Display Not readable

Display Readable

Dark Office Outdoor

Power Savings

Max Setting

Dim Setting

Automatic Transitions

Trend - Display manufacturers are integrating photo diode/transistors on the glass

Set L1, L2 with I2CLight Sensor provides digital readoutOnce Ambient Light level code passes L2 threshold – LED current is automatically adjusted



Ambient Light Detection - ADI

L2_OUT(2) L3_OUT(2) AMBIENT LIGHT LEVEL CONDITION 0 0 Ambient Light > L2 DAYLIGHT 1 0 L3< Ambient Light < L2 OFFICE 1 1 Ambient Light < L3 DARK



Uniformity, Fading and Dimming are key requirements for enhanced user experience

LED Bin Point

Lum

inan

ce

LED Current

Analog Dimming

MAX Current

OFFON

Analog Dimming

Analog Dimming The LED current is reduced to DIM the lightsDigital Dimming The LED current ON time is reduced to DIM the lights

Analog Dimmingnon-uniform intensity and color lightLower EMI and inrush currents

Digital DimmingOffers consistent color and uniform lightTrade-off Increased EMI

FADING IN/OUTLuminance vs LED current is not linearFading requires varying the LED current such that output light is linear



ADI Backlight Controllers Offer Different Fading and Dimming Features

Lum

inan

ce

LED Current

Max Setting

Dim SettingStep FadeFade time = 0

Linear FadeFade time = t

Square Law FadeFade time = t Lu

min

ance

Dim Setting

Time

Step FadeLowest user visual experience

Linear FadeScreen Fades out fast initially and then dims gradually

Square Law FadeScreen Fades out linear in timeBest user visual experience

Ideal Characteristic for Eye

Linear, Square and “Cubic” Law Fades256 steps – Program Min, Max, Fade time, Linear/Square/ “Cube”Eye reacts to relative changes



ADP5501 “Glowfish” Ambient Light Sensing Lighting Management System

-40°C to 85°C

TemperatureRange

Vboost: 24VImax : 31mA

(programmable)

Boost

KEY BENEFITSKEY BENEFITSBacklight Driver

24V Low noise 1.5 MHz to 2.5 MHz PWM Boost with selectable opera24V Low noise 1.5 MHz to 2.5 MHz PWM Boost with selectable operating ting frequencyfrequency

BuiltBuilt--in automatic OVP protection with IRQin automatic OVP protection with IRQ93% efficiency, 4.7 uH 93% efficiency, 4.7 uH –– 10 10 μμH selectable power inductor value H selectable power inductor value (selectable via fuse)(selectable via fuse)

Highly Customizable Ambient Light Management SystemHighly Customizable Ambient Light Management System3 behavior profiles: DARK, OFFICE & OUTDOORS3 behavior profiles: DARK, OFFICE & OUTDOORS

Each profile allows customizable: Max current, Dim current, Dim Each profile allows customizable: Max current, Dim current, Dim timeout, Off timeout, timeout, Off timeout, Fade law, FadeFade law, Fade--in time, fade out time in time, fade out time

programmable trip points & hysteresis for profile transitions wiprogrammable trip points & hysteresis for profile transitions with absolutely th absolutely no flickerno flickerII22C override for 100% customization and controlC override for 100% customization and controlAutonomous mode to completely off load processorAutonomous mode to completely off load processor

Push button display & processor wake Push button display & processor wake -- upup

All lighting functions can be handled with 3 lines to the procesAll lighting functions can be handled with 3 lines to the processorsor

Input Voltage

Single Cell Li-Ion

2.5 V to 4.8 V

Intelligent Lighting ManagementIntelligent Lighting Management&&

Reduced System Power ConsumptionReduced System Power Consumption

24 LFCSP

Package Options

Extensive fading & dimming capabilitiesExtensive fading & dimming capabilities

Actively computes the lowest current needed to Actively computes the lowest current needed to achieve selected brightnessachieve selected brightness



ADP8860Parallel Backlight Controller with ALS

Function/PerformanceCharge Pump based WLED DriverTri-Mode Charge Pump for high efficiency30mA Typical LED currentInternal Soft Start, shutdownUVLO, OVP, Thermal ShutdownAutomatic LED disconnect

FeaturesIndependent Current Sink ControlAutomatic Ambient Light Sense Control

Built in comparator with programmable trip points for Dark, Office and Outdoor ModesIndependent LED sinks with programmable blinking and fade features

I2C Interface control

Small Size20 Bump WLCSP, 24 LFCSP

D3 E3 E4 D4 C4 B4 B3 C3

A2

A1

C1

E2

C2

E1

A3

VoutVDDIO

nRST

SDA

SCL

VinVout

C1+

C1-

CMP_IN

D1 D2 D3 D4 D5 D6 D70.1 uF

1 uF

1 uF1 uF

Photosensor

ADP8860

Vout

0 to 30mA

I2C Interface

Main-Display

Sub-Display

Keypad Light6 LEDs @ 10mA each



Parallel vs. Series Configuration

Parallel LED Configuration ProsNo inductor required – May have less EMI One LED Failure will not disable display5V Process may allow for lower cost, integration into PMUSmaller, Lower Profile Solution

0.5mm Height

Series LED Configuration ProsImproved efficiency across Li-Ion Battery RangeCurrent Matching not an issueInductor size and cost reducing



Parallel vs. Serial Backlight Efficiency

ADP8860 (Parallel) and ADP5520 (Serial) Efficiency Curves

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

2.7 3.2 3.7 4.2Vin (V)

Effic

ienc

y (%

)

ADP8860 - 7 LEDs (Par) @ 220 mAADP8860 - 7 LEDs (Par) @100 mAADP5520 - 6 LEDs (Ser) @30mA



ADP5520 – ALS Backlight Driver with I/O Port ExpanderKEY FEATURESKEY FEATURESBackl

Customiza

Configurable Port Expander

RGB/In

State Machi

ight DriverNonNon--synchronous boost converter operating at 85% efficiencysynchronous boost converter operating at 85% efficiencyDrive up to 6 white Drive up to 6 white LEDsLEDs in seriesin series

ble Ambient Light Management SystemLED current control via a programmable current sink (128 levels LED current control via a programmable current sink (128 levels between 0 and 30mA)between 0 and 30mA)Programmable backlight fade in/out, dim and off timersProgrammable backlight fade in/out, dim and off timersAmbient light sensor for automatic backlight adjustmentAmbient light sensor for automatic backlight adjustment

8 configurable GPIO pins (input, output, up to 4x4 keypad matrix8 configurable GPIO pins (input, output, up to 4x4 keypad matrix))

dicator LED ControllersUp to 3 auxiliary LED current sinks (64 levels between 0 and 15mUp to 3 auxiliary LED current sinks (64 levels between 0 and 15mA)A)Programmable auxiliary LED fade in/out timersProgrammable auxiliary LED fade in/out timersProgrammable auxiliary LED on/off timers (allows blinking)Programmable auxiliary LED on/off timers (allows blinking)

neII22C compatible serial interfaceC compatible serial interfaceInterrupt line for signaling an external processorInterrupt line for signaling an external processorCurrent limit, overvoltage & thermal overload protectionCurrent limit, overvoltage & thermal overload protectionHard resetHard reset

Minimizes lines across the hinge Minimizes lines across the hinge Off loads processor functionsOff loads processor functions

&&Reduces system power consumptionReduces system power consumption

2.2k

2.2k

10k

10k

I/O I/O

Vboost: 24VImax : 30mA

(programmable)

BoostInput Voltage

2.7 V to 5.5 V 4×4mm 24 lead LFCSPPackage Options

-40°C to 85°C

TemperatureRange



ADP5520 “Angelfish” Perfect Application

Pantec Duo

Samsung DMB

HTCSlider

Samsung Dual Hinge

Motorola2 Way Radio

Hand held devices with complex hinges

Any portable device with buttons and a screen valuing • Power Savings • Space savings • SW simplicity

General Portable



Vbatt

VddA

LMUAngelfish

SW BST

BL_SNK

CMP_IN

nRST

nINTI

VddIO1.8 to 2.7V

SCL

1.8 to 2.7V

SDA

Cap_out

3x3 Keys

C0

2.8VAGND

GND 13

GND 14

Vbatt =2.5 to 4.8V

C1 C2 C3R0

KRM 021607

Column 0

Column 1

Column 2

R1R2 R3

A B C

E F G

I J K

ILED

GR B

Applications Diagram

Configurable Port Expander

Supports up to a 4x4 key scan matrix or 8 GPIOs or 3 indicator LEDs or 1 RGB controller.

Ambient light Management System

Supports external photo sensor with 3 programmable brightness modes(Outdoor/Office/Dark)

programmable backlight driver

Accommodates up to 6 WLEDs in series. User defined Max & Dim currents.

I2C for Programming

Optional reset signalFor brown out

Conditions

Programmable Indicator Controller

Dedicated pin for visual indication of network connectivity or charging functions. Programmable autonomous blink and fade sequences

Programmable RGB ControllerIndependently programmable blink, fade and on/off functions

Interrupt to Processor

Ambient Light

Manager

Ambient Light

Manager

Backlight Driver

Backlight Driver

Port Expander

Port Expander

RGBController

RGBController

Indicator controllerIndicator controller



Flexible Use for Different Application

Vbatt

VddA

LMUAngelfish

SW BST

BL_SNK

CMP_IN

nRST

nINTI

VddIO1.8 to 2.7V

SCL

1.8 to 2.7V

SDA

Cap_out

4x4 Keys

C0

2.8V

AGND

GND 13

GND 14

Vbatt =2.5 to 4.8V

C1 C2 C3R0

KRM 021607

Column 0

Column 1

Column 2

Column 3

R1R2 R3

A B C D

E F G H

I J K L

M N O P

ILED

V1=3.0 to 5 V

Vbatt

VddA

LMUAngelfish

SW BST

BL_SNK

CMP_IN

nRST

nINTI

VddIO1.8 to 2.7V

SCL

1.8 to 2.7V

SDA

Cap_out

C0

2.8V

AGND

GND 13

GND 14

Vbatt =2.5 to 4.8V

C1 R3 C3R0

KRM 021607

R1R2

V1=3.0 to 5 V

GP

IO

GP

IO

GP

IO

GP

IO

GP

IO

ILEDC2

GP

IO



Proposed Phone FunctionalityH

inge Connections

53Lines

Display

CameraDisplay

Keys

Display D

ata and C

ontrol15 Lines

Cam

era Data and

Control

I2C

2 Lines15 Lines

Backlight

2 Lines

Backlight

Keypad C

ontrol

6 Lines

Sub B

acklight

2 Lines

Pow

er

2.6V

1.8V

Vbat

Cha

rge

LED

1 Lines

Mis

c

Vibrator

Audio

4 Lines

Light Sensor

2 Lines 4 Lines

Flip Side

Indicator LED

LightSensor



2 Chip SolutionH

inge Connections

14Lines

I2C

AD

P50

250

Dat

a

Mis

c

Ser

ial D

ata



Issue ~ 1¢ / line across hinge processor must control I/O’s

Always on to monitor

Impacthigher cost solutionhigher power consumption

Traditional Hinge Vs. Angelfish Comparison

Value reduced lines across hinge autonomous GPIO control

Processor can go to sleep mode

Impactlower cost solutionlower power consumption

Push button 1Push button 2Push button 3Push button 4Push button 5Push button 6

Ambient Light SensorNetwork Indicator

Hinge or Slider

Power, ground, I2C4

Traditional

Charging Indicator

Power, ground, I2C

Ambi

ent L

ight

Sen

sor

Hinge or Slider

4

Push button 5

Push button 1Push button 2Push button 3Push button 4

Push button 6

ADP5520ADP5520

Angelfish

Interrupt

Net

wor

k In

dica

tor

Cha

rge

Indi

cato

r



Photo Sensor Backlight Controls

L3programmable

Dark Office Outdoor0mV

30mV

Brightness

L3 L2 Function

0 0 Outdoor mode0 1 Office mode1 0 N/A1 1 Dark mode

Processor can read the status.ADP5520 automatically does the

Adjustments.

Max_curr: programmableDim_Curr: programmable



L2programmable



Intelligent Backlight Controller reduces real time software

User InputBL O

N

BL FADETo DIM

BL FADETo OFF

User Input

BL ON

Polling Ambient Light Sensor

Office Outdoor

Polling Ambient Light Sensor

Office Outdoor

BL FADETo Outdoor setting

LED Current Office Setting

OFF Setting

DIM Setting

Outdoor SettingSquare Law Fade

Time Sensitive I2C writes

Intelligent Backlight Controller

Software base Controller



System Advantage

Autonomous operation improves System EfficiencyHardware OptimizationMinimize the load on the processorBacklight controlled by LMU not processor

Backlight ControllerBacklight consumes 1/3rd of the battery budget

Software control requires processor interactionSimple, autonomous control of backlight timers, fade-in, fade out will save power

Ambient Light SensorsOptimizes the display light power consumption based on ambient light. Over 50% power savings in Standby



Stand-By Time Analysis

0

50

100

150

200

250

300

0 4 8 12 16 20 24 28 32 36 40

User Interrupts

Hou

rs

Software ControlHardware ControlWith ALS

Over 50% Improvement in Stand-by time

User Interrupt Display turns on for 10secs and DIM for 2secs

Autonomous Backlight Control15% Improvement in Standby

time

Backlight + Processor

Battery Capacity = 1100mAH

Assumptions• 4 LEDs

• 20mA (Bright Mode)• 10mA (DIM Mode)

• ARM Processor = 20mA• Use scenario

• 25% Outdoor• 60% Office/Indoor• 15% Indoor

With ALS 50% improvement in Standby time



Presented By:Justin Zhao

Application Manager - Portable Power

Analog Devices, Inc.22/F, One Corporate Avenue222 Hu Bin Road, Shanghai, 200021, ChinaOffice: 86-21-2320-8088Mobile: 86-1376-122-5504EMAIL: [email protected]


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