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Advanced LED Backlighting Technology
Justin ZhaoNov 1st, 2008
Including ALS (ambient light sensing), dimming & fading, fun-lighting, etc..
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— 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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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— China Power Technology Forum 2008 —
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
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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
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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
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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
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2 Chip SolutionH
inge Connections
14Lines
I2C
AD
P50
250
Dat
a
Mis
c
Ser
ial D
ata
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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
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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
Max_curr: programmableDim_Curr: programmable
Max_curr: programmableDim_Curr: programmable
L2programmable
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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
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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
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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
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— China Power Technology Forum 2008 —
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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