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TM
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
TM
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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3Freescale™ 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.
Target Applications
LCD-TV – 22%
Notebook – 27%
Monitor – 39%
Automotive – 2% Picture Frame – 2%
Industrial – 2%
Portable DVD – 5%
TM
4Freescale™ 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.
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
TM
5Freescale™ 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.
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
TM
6Freescale™ 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.
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
TM
7Freescale™ 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.
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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8Freescale™ 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.
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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9Freescale™ 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.
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
TM
10Freescale™ 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.
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
TM
11Freescale™ 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.
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
TM
12Freescale™ 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.
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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13Freescale™ 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.
►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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14Freescale™ 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.
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
TM
15Freescale™ 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.
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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16Freescale™ 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.
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
TM
17Freescale™ 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.
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
TM
18Freescale™ 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.
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
TM
19Freescale™ 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.
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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20Freescale™ 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.
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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21Freescale™ 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.
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
TM
22Freescale™ 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.
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
TM
23Freescale™ 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.
MC34844 Introduction
►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
TM
24Freescale™ 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.
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
TM
25Freescale™ 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.
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
TM
26Freescale™ 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.
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
TM
27Freescale™ 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.
MC34846 Introduction
►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
TM
28Freescale™ 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.
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
TM
29Freescale™ 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.
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
TM
30Freescale™ 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.
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
TM
31Freescale™ 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.
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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32Freescale™ 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.
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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33Freescale™ 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.
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
TM
34Freescale™ 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.
►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.
34
Q&A
TM