Lighting Solution (HBLED General Lighting and CCFL and LED …read.pudn.com/downloads100/doc/project/410449/ccfl.pdf · CCFL is the short form of Cold Cathode Florescence Lamp CCFL

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. 2007.

Lighting Solution (HBLED General Lighting and CCFL and LED Backlight Solution)

Mars Leung

November 2007

PC317

TMFreescale™ 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. 2007. 2

Abstract

CCFL is commonly used for LCD screen as backlightIt requires several to teens of hundred volts of AC for its operationIn usual application a DC-AC inverter is required to power itIn the past, analog PWM controller is dominating in DC-AC inverterWith the lowered cost and higher processing power of MCU it is

possible to replace the analog controller with added flexibility in control algorithm and functionality

This training will cover different implementation of CCFL controller with an 8 pin MCU – MC9S08QD4


Agenda

What is CCFLInverter TopologyDimming MethodologyMCU Solution

TM


What is CCFL ??


What is CCFL

CCFL is the short form of Cold Cathode Florescence LampCCFL is a low-pressure discharge lampIt is constructed with a glass tube coated on the inside with

phosphor and the tube is filled with mercury vapor at low pressure

HgHg

HgHg

Hg

HgHg

Mercury vapor and filling gasRGB tri-phosphor coating


How CCFL Works

Applying sufficiently high voltage to the lamp via the cathodes cause arcing inside the tube

When the arcing electrons collide with mercury vapor ultravioletradiation is emitted

When the ultraviolet radiation radiates onto the phosphor visible light is emitted

HgHg

HgHg

Hg

HgHg

e-

e-

e-e- e-

e-e- e-

HgHg

HgHg

Hg

HgHg

HgHg

HgHg

Hg

HgHg

Hg

HgHg

Hg

Hg

Hg

Hg

Hg

Hg

e-

e-

e-

+


Some Characteristics of CCFL

CCFLs are often driven with a 20 – 100 kHz sinusoidal waveform• CCFL is functional when driving with DC yet this cause rapid

degradation, darken side and uneven brightness• Sinusoidal waveform creates less significant EMI• The most common frequency is about 40 – 60kHz

CCFL degrades as it operates known as aging• Due to degradation of phosphor and Hg consumption• Ion bombardment from the discharge column may be the attributing

factor in depreciation of the Phosphor• Ion bombardment of the phosphor over a period of time can cause the

inner surface of a phosphor coating to become non-luminescent• Ion bombardment over time can cause some phosphors to have a

greater tendency to absorb mercury• Lamp life defined as the brightness decreased to 50% of the original• Typical lamp life range from 10000 – 60000 hours


Some Characteristics of CCFL

Lamp size (diameter and length) substantially influences electrical dynamics and research shows that

• Higher voltage is required to drive longer lamps (e.g. 30cm lamps driving voltage is about 600V and 60cm is about 1000V

• Higher voltage is required to drive lamps of smaller diameter• Degradation is less obvious in lamps longer and of larger diameter

Under low temperatures CCFLs suffer from flicker and are less intensive

High temperatures shorten tube life

TM


Inverter Topology

TM


Royer InverterRoyer


Royer Inverter Functional Diagram

Buck

Cr

Q1

Q2

L1~100uH

Vin

DVin ⋅22

π

N1/2 turnsL = Lp/2

N3

N1/2 turnsL = Lp/2 N2 turns

R2

Ballast Capacitor C2

R1


Simple Calculations

( )

lampp

P

brP

r

br

lamp

in

strike

INI

L

CNCLf

CfI

VV

NNN

⋅=

+⋅≈

⋅=

⋅⋅

==

currentprimary by the calculated becan ratingcurrent Transistor20uHabout of range in theusually is

22

2

1elyapproximat isFrequency Resonant

voltageoperating lamp the times2about toVSelect 2

V

Value eCapacitancBallast

2

ratio Turns

2

cb

cb

1

2

π

π

π

The calculation for Royer Inverter can be very complicated but here shown only a simplified version


Royer Inverter Features

Royer inverter is a self oscillating circuit• The switching frequency is determined by the inductance of the primary

of the transformer, the parasitic capacitance, the resonant capacitance, the load capacitance etc.

• Thus the switching frequency cannot be controlled precisely• You get a nearly sine wave output waveform

Usually require a buck converter before supplying to the inverter thus the cost increased and efficiency decreased

• The lamp brightness is not sensitive to the input voltage as the buck converter is in place

• Lower efficiency, hardly over 75%Larger Size

• Require 3 primary windings• Higher component count

Require a relatively large inductor to provide constant currentRequires a resonant capacitor


How Does the Royer Inverter Works

Buck

+

+

Vin

Q1

Q2

N3

Cr


How Does the Royer Inverter Works

Buck

+

+

Vin

Q1

Q2

N3

Cr

TM


Push-Pull Inverter


Push-Pull Inverter Functional Diagram

Vin

T1

T2

T1, T2 are n-channel enhancement mode MOSFETs

N1/2 turns

N2 turns

N1/2 turns


Simple Calculations

OUTin

in

OUT

IrmsNNI

VVrms

NN

×=

⋅=

1

2

1

2

currentInput 21


Push-Pull Inverter Features

PWM driving the pair of transistor instead of self resonant oscillate circuit

• The frequency of operation depends on the driving PWM only• Output voltage can be controlled by varying the on time of the transistor

Smaller size• Require 2 primary winding• Does not require a buffer inductor and resonant capacitor• A buck converter is not needed

Higher conversion efficiency• A buck converter is not needed

The output waveform is not as close to sine wave as Royer inverter• Since the driving waveform is a square wave and rely on the loading

characteristic to filter out the other frequency components


How Does the Push-Pull Inverter Works

Vin

+


How Does the Push-Pull Inverter Works

Vin

+

TM


Full Bridge Inverter



T1

T2

T3

T4

Vin

Vin

T1, T3 are p-channel enhancement mode MOSFETsT2, T4 are n-channel enhancement mode MOSFETs

N1 N2



Similar to half bridge topology but instead of single end of the supply is fixed both end are switch controlled

2 complementary pair of PWM is needed• In the first half cycle T3 is on when T2 is on,T4 and T1 must be off• In the next half cycle T1 is on when T4 is on, T2 and T3 must be off

Require 4 MOSFETs• 2 p-channel and 2 n-channel

Wider input voltage range accepted


How Does the Full Bridge Inverter WorksVin

Vin+

T1

T2

T3

T4

N1 N2


How Does the Full Bridge Inverter WorksVin

Vin

+

T1

T2

T3

T4

N1 N2

TM


Half Bridge Inverter


Half Bridge Inverter Functional Diagram

T1

T2

Vin

T1 is p-channel enhancement mode MOSFETsT2 is n-channel enhancement mode MOSFETs

N1 N2


Half Bridge Inverter Features

1 complementary pair of PWM is needed• In the first half cycle T1 is on when T2 is off• In the next half cycle T2 is on when T1 is off

Require 2 MOSFETs• 1 p-channel and 1 n-channel

Require higher turns ratio


How Does the Half Bridge Inverter WorkVin

+

T1

T2

N1 N2


How Does the Half Bridge Inverter WorkVin

+

T1

T2

N1 N2

TM


Dimming Methodology


Dimming Methodology

Common Dimming Methodology includes• Dimming by Modifying the Burst of Driving Waveform• Dimming by Modifying the Pulse Width of the Driving Waveform• Dimming by Modifying the Frequency of the Driving Waveform

See detail in the following slides


By Modifying the Burst of Driving Waveform

This dimming method can be applied to any type of CCFL drivingBy periodically enable and disable the driving waveform supplied to the

CCFL with a burst frequency at about 100 – 200HzBy varying the on-time and off-time ratio of the burst frequency we can get

the light visually dimmedVery high dimming ratio (up to about 100:1) is achievable (this depends on

the CCFL, the driving frequency and the burst frequencyAlmost linear dimming is achievable Note that

• Flickering will be seen when the burst frequency is low• Moving banding will be seen if the burst frequency is closed to the screen

vertical frequency• The quality of the transformer, PCB layout (which affects the EMI radiation) and

the decoupling from the audio circuit is very important as the burst frequency is in the audio frequency range

• While the CCFL is off the gas inside the tube is remain ionized thus no need to strike again. Applying this should consider the off time carefully


By Modifying the Burst of Driving Waveform (Royer)

Burst period : approx 5 – 10ms

Duty cycle 1 – 100%

CCFL on during this period

CCFL off during this period

The CCFL off time should not be too long to have the gas inside the CCFL remain in plasma state


By Modifying the Burst of Driving Waveform (Direct Drive)

Burst period : approx 5 – 10ms


CCFL on during this period

CCFL off during this period

The CCFL off time should not be too long to have the gas inside the CCFL remain in plasma state


By Modifying the Pulse Width of the Driving Waveform

This dimming method can be applied to direct drive type CCFL inverter (push-pull, half bridge, full bridge)

The driving frequency of the power MOSFET is fixedDimming is achieved by varying the time the power MOSFET is

switched onLonger the MOSFET on time, higher the voltage seen at the

secondary outputThe output voltage to drive the CCFL is varied thus dimming the

CCFL


By Modifying the Pulse Width of the Driving Waveform

Maximum Brightness

Medium Brightness

Minimum Brightness


By Modifying the Frequency of the Driving Waveform

This dimming method can be applied to direct driving type CCFL (push-pull, half bridge, full bridge)

The time the driving MOSFET is on is fixed, dimming is achieved by varying the time the MOSFET is switched off

The output voltage to the CCFL is roughly fixed but the average power delivered to the CCFL is changed thus dimming the CCFL

As the on time is fixed the energy transfer and the voltage at the secondary is almost constant yet the longer the off time the lower the average power delivered to the secondary output


By Modifying the Frequency of the Driving Waveform

Maximum Brightness

Minimum Brightness

Medium Brightness

TM


MCU Solution


MCU Solution

Not many MCU solution provided by semiconductor vendor yetCustomer is shifting to consider using MCU as the PWM controllerCurrently system cost of MCU solution and analog solution is similar and

MCU solution is expected to gain popularity due to• lowering cost of MCU• More flexible in changing control parameter• More complex control and protection algorithm could be implemented• MCU provides communication capability• Functions like soft start, open lamp, short circuit, over current, over/under

voltage can be implemented easily with firmware and thus save some external components and system cost

Only requires simple coding• Code size about 1K

Yet programming an MCU could be a hurdle for customer to shift to use MCU

• We had written code for Royer inverter and push-pull inverter• You can use it as a starting point to support customer writing the code


Advantage of CCFL Backlight Controller MCU

ADC for connecting various sensor• Light sensor for automatic brightness control• Lamp brightness monitoring/control• Temperature sensor • Lamp operating range monitoring and protection

16 bit timer for flexible timing control• Flexible dimming PWM frequency• Synchronize dimming PWM with external event• Flexible soft-start/soft-off control

Built-in trimmable, programmable output frequency oscillator help lower system cost

MCU enables various functionality• Communication with system host controller• Programmable lamp characteristic• Fault reporting


An Application Example of a Royer Type Inverter

+ C410uF 16V

2

3

5

6

1

8

7

4

T1 PX190664

C81uF

123456

JP1 BDM

1 2C1

27pF/3kV

1 2

C60.15uF

+5V

PO

WE

R_O

N

R31K

R930

0R

1

3 2

D4BAV99/SOT

123

J1

CCFL1

Q3FZT849/SOT

123

J3

CCFL2

+5V

R5100R

R6 0R

R7 OPEN

R1456k

21

D1

LED0805

R17OPEN

23

1

Q1MMBT3904

1234

J4

EXT CTRL

+5V

R24 0R

VOUT max 1500V

R15

0RPWR

BRIGHT

123456

J2

CON6

IOUT max 18mA total8mA per lamp normal

10:10:2:1:1445

R160R

PTA51

PTA42

VDD3

VSS4

PTA35PTA26PTA17PTA08U1

MC9S08QG4/SOIC8C90.1uF

F13A

+

C2200uF 25V

BR

IGH

TNE

SS

R80R

RESETbBKGb

R10

300R

R140R

BRIGHT

L1

100u

H/2

A

Q2FZT849/SOT

31

D2

BZX

84-B

5V6

R210K

31

D3

BZX

84-B

5V6

PWR

+C3

47uF 25V

12C5

27pF/3kV


Royer Type Inverter Demo Board Features

Royer Type Self Oscillate 50kHz DC-AC InverterSupply Voltage 12V 1AOutput Voltage ~1.2kV 8mAPWM Dimming. Frequency up to 1kHzDigital/Analog/Photo Dimming Control Algorithm Implemented2 Lamps of Length 30cmOpen Lamp and Over Current ProtectionSoft-Start and Soft-OffLamp Aging Tracking (Patent in Process)


Royer Type Inverter Demo Board Photo


An Application Example of a Push-pull Type Inverter

+5V

T1

3

6

8

1

7

2

4

5

R20 0R

J2

CON6

123456

R31K

+24V

R19 0R

R8open

R140R/1206

R17open

+ C410uF

R1856k

R210K

R1160K

PTA2

+C3

47uF

R16500R

U1

MC9S08QD4/SOIC8

1234 5

678

PTA5PTA4VDDVSS PTA3

PTA2PTA1PTA0

R10240K

R120R

BKGb

JP1 BDM

123456

+

C2200uF

R130R

PTA5

+5V

C1

33pF/3kV

1 2

R70R

F12A

J1

CCFL1

12

C60.1uF

PO

WE

R_O

N

Q2NDS4559/SO

2

3

4 5

7

1

6

8

Q12N3904/TO92

23

1

C80.1uF

R140R

C5

33pF/3kV

12

C71uF

R4100R

D2

BZX

84-B

5V6

31

R50R

J3

CCFL2

12

RESETb

D3BAV99/SOT

1

3

2

R15500R

+24V

R6open

Q3NDS4559/SO

2

3

4 5

7

1

6

8

BR

IGH

TNE

SS

J4

EXT CTRL

1234

R90R

D1LED0805

21


Push-pull Type Inverter Demo Board Features

Push-Pull Type 50kHz DC-AC InverterSupply Voltage 24V 0.6AOutput Voltage ~2x1kV 6mALamp Length 64cm x 2PWM Dimming by modulation of 200Hz PWM or by modifying the

pulse width of the driving PWMDriving PWM 50kHz with adjustable pulse width from 35% to 50%

(minus dead time)Dead time from 100 – 400nsDigital/Analog/Photo Dimming Control Algorithm ImplementedOpen Lamp and Over Current ProtectionSoft-Start and Soft-OffDriving and Dimming Waveform Always Synchronized


Push-pull Type Inverter Demo Board Photo


PWM Driving Waveform of Push-pull Type Inverter

Min : 20μs

Dead time0/200/400ns

10 to 13μs + 2*Deadtime

7 to 10μs - 2*Deadtime


Waveform for Dimming by 200Hz PWM modulation

Max : 5100μs (255*20μs)



Output Waveform


Waveform at MOSFET

Vgate1

Vdrain1

Vgate2

Vdrain2


Real Life Photo


Real Life Photo

TM


LED Lighting SolutionPC317

Nov 29, 2007

Dennis LuiSystem Engineer


Agenda

LED Lighting Solution

• Introduction• Microcontroller-based HB LED drivers• Solution Examples

KA2 HB LED SolutionMR16 Form Factor SolutionSOS Flashing LED TorchQG4 White / RGB LED Backlight DriverSystem in Package (SIP)Light-Box Demo

• Summary

TM


Introduction to HB LED LightingIntroduction to HB LED Lighting


Introduction to HB LED Lighting

HB LEDs are lighting the world!!! This semiconductor technology is bringing the benefits of Solid State Lighting to general lighting applications

General lighting and other new marketsOutdoor signageTraffic signaling LCD Backlighting/DisplaysAutomotiveAvionics


Advantages of LED

•• Reliable (100K hours) Reliable (100K hours) –– Reduced Maintenance CostsReduced Maintenance Costs•• More Energy Efficient More Energy Efficient –– Be the Environmental SolutionBe the Environmental Solution•• Flexible Size and Shape Flexible Size and Shape –– Design FlexibilityDesign Flexibility•• Vivid Saturated Colors Vivid Saturated Colors –– Without FiltersWithout Filters•• Robust Robust –– Vibration ProofVibration Proof•• Instant On and Fully Dimmable without Color Variation Instant On and Fully Dimmable without Color Variation –– PWM PWM

ControlControl•• No Mercury No Mercury –– Environmental RegulationsEnvironmental Regulations•• LowLow--Voltage DC Operation Voltage DC Operation –– Eliminate High voltage connectionsEliminate High voltage connections


LED Cost down

TM


Microcontroller-based HB LED drivers


Buck Converter

ON

OFFSW1

ISW

IDIODE

IL

t

t

t

t

High side switching is realized as a Buck converter:

When SW1 is ON, L is energized;

When SW1 is OFF, stored energy in L continues to drive RL


Steady State AnalysisConverters is operating in continuous conduction mode (CCM)Invoke Voltage-Second Balance Equation across L.

Ideal Case: VDIODE=0:

(VIN – VO)DTPERIOD = VO(1 – D)TPERIOD

VO/VIN = D (<1)where

TON = DTPERIOD; TOFF = (1-D)TPERIOD


Steady State AnalysisL current can be shown

IL(ON) = (VIN – VO) x TON/LIL(OFF) = - (VDIODE – VO) x TOFF/L

Knowing VIN, VO, D, TPERIOD, IRIPPLE, L can be deduced

For example, VIN=5V (Supply Voltage), VO=3.85V (LED VF), D=3.85/5, TPERIOD = 1/30kHz, IRIPPLE = 350mA x 25%

L = (VIN – VO) x D x TPERIOD/IRIPPLE = (5-3.85) x 3.85/5 x 1/30k / (0.35 x 0.25) = 337uH


Feedback Control

• To maintain the LED in constant current, close loop control must be applied

• Use low Ohmic resistor as a current sensor• Current sensor convert the LED forward current into voltage• Over current →reduce D, reduce TON• Under current →increase D, increase TON• ADC or analog comparator is needed for feedback.

1Ω

ADC / ACMP-MCU

TM


Solution Examples

TM


KA2 HBLED Demo


HB LED RD Buck ConverterFeatures:

• High Brightness LED driver with 350mA current driving capability

• Control a buck converter to regulate supply voltage to match with various HB-LED forward voltage requirement

• Up to ~80% efficiency

• Internally generated, ~30 KHz PWM Switching Frequency

• Feedback control on LED forward current thru a current sense resistor

• Dimming control by two GPIO pins

VDD = 5V

Vref

PWM(MTIM)

Vout

MCUControl

FB

Key

ACMP

VDD

GND DIM0

VDD

Rs

KBI

DIM1

RS08KA2

PWMPMOS


HB LED Load HandlingUsing KA2 internal Timer and Analog

comparator modules to implement a Buck Regulator.

A simple buck converter is implemented to convert a 5V input supply to a current regulated output for LED driving.

The MCU generates a 8-bit resolution PWM (~30KHz) signal using the Timer Interface Module to control the switching duty cycle of the PMOS device.

The LED current is monitored by a current sense resistor Rs and transferred to a voltage level (VRs) which can be detected by ACMP module.

Base on the feedback voltage, the MCU will adjust the PWM duty cycle in close-loop control to keep the LED driving current as a constant. (e.g. increase duty cycle if feedback voltage is less than comparator ‘s Vref voltage)

IL IO

Time

PMOSON

Time

OFF ON OFF ON OFF

PWMOutput

T=~33us

VRsACMP Ref

TimePWMOutput

increaseON duty

decreaseON duty

Hysteresis

Inductor Current

Feedback Voltage


HB LED RD Software

Initialization

Detect Feedback Voltage

FB higher than ACMP ref ?

No

Decrease PWM ON time

Detect KBI and modify DIM0/1

NoNo

Yes

Yes

No

Increase PWMON time

Software Implementation

The 8-bit Modulo Timer is configured to generate the PWM signal. The Timer is running in Module mode such that the overflow flag will be set if the counting value matches the modulo value.

The function of the ACMP comparison loop is to control the PWM duty cycle periodically when it detects a error between the feedback voltage and the reference voltage.

When a key pressing event is detected in KBI routine, the output states of DIM0 & DIM1 will be changed to setup a new reference voltage for ACMP.


HB LED RD Software

PMOSON

Time

OFF ON OFF ON OFF

PWMOutput

Total Period = PWM ON + OFF + S/W overhead

MTIMMOD = PWM ON

MTIM OverflowMTIMMOD = PWM OFF

MTIM Overflow again

Detect KBI, Check ACMP resultand adjust PWM ON/OFF values

MTIMMOD = Updated PWM ON

Overhead

SoftwareOverhead

PWM and Feedback loop Implementation.PWM output can be achieved by programming two timer overflow variables (PWM ON and PWM OFF) alternatively into the MTIM Module Register.

The PWM control range is determined by the values of PWM ON and OFF time. These two variables should be adjusted in opposite polarity such the the overall period is keep constant. (e.g. PWM ON plus 1 => PWM OFF minus 1)

The overall PWM period is equal to sum of PWM ON, PWM OFF and the time using in software looping for KBI / ACMP…etc.

The PWM ON and OFF values will be updated according to the result of analog comparator output which is used as a feedback signal to tell us whether the LED current is higher or lower than the expect level.

TM


MR16 Form Factor Light Bulb


Features of MR16 LED Bulb SystemDrop-in Replacement for standard MR16 halogen type format (longer life, no fragile glass, no mercury)Low power consumptionDC 12V Input Voltage3W Ultra High Brightness LEDBulk topologyConstant LED Current (700mA)Soft-Start Control and Over-Current ProtectionDimming Control without additional wiring (advantage for Flash MCU)


Low Cost MCU Based MR16 LED Bulb System

FeaturesFeatures ::

•• Low cost and Low cost and compact design with compact design with all electronic all electronic components housed components housed into a into a ““MR16MR16”” form form factor lighting modulefactor lighting module

•• Intelligent control via Intelligent control via user input, or self user input, or self detection via power detection via power lineline

•• Safety protection is Safety protection is possiblepossible


Functional Description

The power MOSFET switching is controlled by MCU PWM output and the LED current is monitored by ADC module thru a current sensing circuit.Base on the feedback voltage, the MCU will adjust the PWM duty cycle in close-loop control to keep the LED driving current as a constant.The dimming level can be adjusted by changing the regulated LED current directly which is proportional to a target value using in the ADC comparison loop.The pre-set dimming levels (target values) are stored in MCU Flash memory. When the system is power on, the previous dimming level will be restored from memory for brightness setting. The current dimming level will be saved in memory again if the system is operated more than 12 second, otherwise the next step dimming level will be recognized as the configuration for next power on brightness setting.There is no additional control signal for dimming setting; only the power on time is used.


Dimming Handling

POR

Retrieve Saved Level from Flash

Save Next Level to Flash

Wait 12s

Save This Level to Flash

Brightest

Dimmest

Stack of Pre-defineDimming Level

NextLevel

Saved PointerFLASH

TM


SOS Flashing LED Torch


Features of LED TorchMulti-level Dimming Control with 100/75/50/25% BrightnessDC-to-DC Buck Converter with Constant Current RegulationUp to 350mA LED Forward Current~80 Efficiency for 1 W High Brightness LEDFlashing Mode for EmergenciesStandard “SOS” Pattern orOther flashing sequences pre-set by manufacturer in MCU Flash memorySingle Button Switch for Mode Selection

ON / OFFDimming Scan modeFlashing mode

Compact SizeDC 6V Input Voltage (4x1.5V AAA Batteries)


Low Cost MCU Based LED Torch

Rs

VF

908QT2908QT2Iout

PWMControl

ADC

Vin(6 V)

ConstantConstantCurrentCurrentControlControl

Button Switch

(3 V)

Current Sense &Level Shift


Features of LED Torch

Mode Selection:

1. ON ModePress once and release the button within half second

2. Dimming Scan ModePress and hold the button longer than one secondThe brightness level will be switched cycle through various dimming levels and stop scanning when the button is released

3. Flashing ModePress and release the button twice within two secondsThe pre-set “SOS” flashing sequence is generated continuously

4. OFF ModePress and release the button again during any operating mode

TM


QG4 White / RGB LED Backlight

Driver


Specifications

Inputs• Power supply Vin = 7V to 16V DC• On/Off control input

High ON, Low OFF, 3V or 5V.• Digital Burst Control input

Direct Burst control mode - hard wired (250Hz to 10KHz)SMBUS burst control mode (status read available)Buffered burst control mode (local burst freq. conversion)ON/OFF control at 3V or 5V

Outputs• Vout = 30V DC (20V to 40V)

80KHz PWM Boost circuit (PWM resolution = 125)Minimum drive voltage detection (95% high efficiency)Loading = 180mA (30mA x 6)Cycle to cycle over-voltage protection (by ADC readout)

• 6 Channels constant current outputsShort circuit protection (limited current when shorted)Power on short circuit detection and protectionOpen circuit detection and protection (by ADC readout)Independent channel duty control possible (for RGB LED)

Vout

OUT1

OUT2

OUT3

OUT4

OUT5

OUT6

Vin

ON/OFF

Burst_in

SCL

SDA

Driver Board


System Block Diagram

Freescale LED Backlight Driver Block Diagram• MCU: MC9S08QG4 16pin• MCU Bus clock = 10MHz• 80KHz PWM resolution = 125

Boost 47uH

ADC1-6

x10 LEDs

x 6 in parallel

10MHz / 33

80-300KHz PWM

QG4 16pin

ADC0

3.3V Reg

Vin

On/Off /RST

Burst in

45V protection

Current Feedback

20V – 40V 7V to 16V

250Hz to 10KHz

SCL

SDASCLSDA


Demo Board

MCU

InductorJ1

BDM

3 cm

3 cm

J2

12V

EADIM

GND

SCLSDA

LED BarLED Bar

LED BarLED Bar

LED BarLED Bar


Application Sample6 Parallel LED Backlight Driver Sample

• Configuration #1: 6 parallel White LED bars• Configuration #2: RGB LED bars with independent duty control for each R,G,B channel

ADC1-6

x10 LEDs

6 RGB barsHV

HV out

QG4 Driver Board

BURST IN

Vin

On/Off /RST

Burst inCurrent Feedback x 6

30V

12V

Analog or Digital

SCL

SDA

SCLSDA

VCC

RGB Independent Duty Control x 6

Option

6 W-LED bars or

TM


System in Package (SiP)


System in Package (SiP)

System in Package Solution, using the most optimized technologiesHigh integrated products – optimized per applicationSmaller Footprint requiring reduced PCB space


MM908E625 Features

The 908E625 is a highly integrated single-package 8-bit solution that includes a high-performance HC08 microcontroller with a SMARTMOS™ analog control IC.

• High-performance M68HC08 core• 1616K on-chip flash memory• 512 Bytes RAM• Two 16-bit, 2-channel timers• 10-bit ADC• Three 2-terminal hall sensor inputs• Four low-resistive half-bridge outputs• One low-resistive high-side output• 16 microcontroller I/Os


MM908E625 Current regulator

The MM908E625 has a current regulator functionality built into each of it’s 4 half bridge low side outputs.

• Current limit circuitry turns off the Mosfet when programmed limit is reached

• Circuitry regulate by re-adjusting the duty cycle of the switching frequency

• Current trip point level is programmable with 6 different settings

55, 260, 370, 550 and 740mA

• Switching frequency is 25KHz max provided by Timer OUT of Microcontroller

+-

S

R

RC

Fgen

FLIP FLOP

L

Vref I

Q

Vs

Internal to MM908E625


High-Brightness LED 908E625 Board

• Features the 908E625 MCU• I/O emulating SPI communication to

MC13192 RF transceiver• SMAC 4.1 to control the MC13192• Buck regulator implementation to

drive high-brightness LEDs• Capable of driving 4-350 mA

highbrightness LEDs• Internal low-side MOSFETS using

current limitation feature• 100 Hz PWM with 20 steps for LED

dimming• Code Size: 4381 Bytes• RAM Size: 132 Bytes

General purpose platform that allows users to prototype their high-brightness LED solutions. It also demonstrates the Freescale-integrated solution using general purpose microcontrollers, analog devices and intelligent distributed control ICs.

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Light Box Demo Light Box Demo


LED Light-Box Demo

This demo is a MCU controlled LED color mixing light source for LCD backlight or general lighting applications


LED Light-Box Demo

Design Challenges:

Implement an accurate color light source.Extend the control range on brightness level.Tracking on color balance for different brightness settings.Resolve the flickering effect Support various standard control interface, SCI / SPI / IIC…etc.


LED Light-Box Demo

PWM

SCI

KBI

AW60 PWM

ADC

Key SwitchDetection

GPIO Port

RS232Interface

To PC

12 Power Supply DC/DCConverter

Red LEDs

Green LEDs

Blue LEDs

I/O Control

System Block Diagram


Linear LED Driver

Features• Individual control block for DC2DC and

LED Driving• Constant current control thru linear

regulationPros

• Fast ON / OFF response time • Support high frequency PWM dimming • Accurate and wide range control on

dimming levelCons

• Power loss at linear driver stage

SW

Vin Vout

SwitchingControl

Ref

PWM

LEDs

Vref

DC2DC FB

MCU

Rs


Firmware Flow – Main Program

Display control menu through SCI

Yes

No

Initialization

SCI Input Mode Operation?

Enable I/O for PCB button detection

YesNo

Valid command from PC ?

Process commands and adjust PWM output

YesNo

Any PCB button pressed ?

Adjust PWM output according to button event

*Standalone demo box without PC control


Firmware Flow– Adjusting PWM Output

Auto White balance?

Adjust PWM width in next PWM cycle

Calculate the two remaining channels PWM values according to existing Color Temperature

PWM value input to one channel

Yes

Get the other two channel values from user input

No


LED Box Demo - Control Menu

Command keys used for different controls

Display of existing parameters andPWM values

Prompt for PWM value input


Demo 1 - Demonstration Mode• The LED Light-Box will display different colors and then light up RED, GREEN, BLUE

and WHITE with increasing intensity.

Demo 2 – Preset Colors Display• The output will be switched to another preset color after “Tab” key has been pressed

each time.

Demo 3 – Auto White Balance Control• The RED and BLUE PWM values will be adjusted automatically to keep the output at

the existing color temperature.

Demo 4 – PWM Output Frequency Control• The flicking phenomenon is more significant at the lower frequency such as at 30Hz. It

can be removed by setting PWM to higher frequencies.

Demo 5 – Full Manual Control• Fully control on R/G/B PWM settings.

LED Light-Box Demo : Demo Examples

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Summary Summary


Brochures


Summary

Applications Freescale Devices

Features Benefits

General Lighting

KA2 / QD2 Timer / ADC / ACOMP Low pin count Temp sensor

Current and Dimming control Low cost Avoid overheating

Handheld KA2 / QG4 Low volt operation Flash for pattern storage Low pin count

Power saving Pattern blinking Small size

Automotive MM908E625 Integrated device (Analog + MCU)

Optimized per application Small footprint

Color Control AW16/32/60 High resolution PWM control Communication interface (IIC/SPI/SCI)

Accurate color control User friendly control menu PC Host communication

Wireless MC13201/2 / MC13211/2/3

ZigBee-compliant Platform Integrated Transceiver Low power modes Ultra low component count


SummaryAdvantages of Freescale Solutions:

• Freescale offers microcontroller-based LED drivers to secure constant current drivers.

• Our intelligent driver solutions contain constant-current controls to configure the LEDs operated in a rated forward current, power saving feature to limit the loss on LED driving stages and over-temperature/voltage/current fault detection to protect the system.

• With user friendly communication interface, users can control the parameters and generate correct colors for a particular application.

• Provide technical supports on microcontroller portfolio, and to help make your design process easier.

• Provide a number of development tools and reference designs to get you started.

TM


LED Backlight SolutionPC317

Nov 29, 2007

Dennis LuiSystem Engineer


Agenda

LED Backlight Solution

• Market Overview• Advantages of LED Backlight• LED Backlight Module• Concerns With Using LEDs for Backlight• Freescale Solution• Summary

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Market OverviewMarket Overview


Market Highlights• LCD TV shipment rapid growth in the next few years makes LCD TV to become a major

market share in large screen display to replace the transitional CRT TV due to screen size, thickness and less radiation of TV

• The worldwide consumption TAM units for LCD TV (>=26”) is growing very fast at CAGR 42% from 2005 (13.3Mu) to 2010 (77Mu)

• LED will be used to replace CCFL as the lighting source of the LCD backlight due to longer life time, RoHS compliance (mercury-free), widen color gamut, better color performance (dimmable, reduction in motion artifacts)

• We need to handle wide range HB LED devices’ characteristics and provide LED aging & compensation in order to keep good display uniformity. The color management solution can also be applicable for color filter and color filter-less panel. Moreover, the system architecture is also scalable for various screen sizes

• The SAM for LED BLU in LCD TV (>=26”) is $580M in 2010. SAM for LED BLU in high end monitor (>=20”) is $260M in 2010. SAM for LED BLU in medium & small size LCD (<9”) is $620M in 2010.


Breakdown of existing LCD panel cost

Source: DisplaySearch Nov, 2004

• Cost for Backlight & Color Filter increased in large-sized panel


Market Analysis

Cold Cathode Fluorescent Lamp (CCFL) is the traditional solution for LCD backlight. However, the color quality and image quality are not as good compared with CRT. Customers are looking for better quality

For high-end monitor (≥20”), they will be used for publishing machines and true color performance is expected

For medium & small panel size (<9”), reduction in motion artifacts is one of the key benefits. Moreover, the resolution will be improved 3 times if color filter-less panel is used

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Advantages of LED Backlight


Source : OSRAM

Color Gamut of LED & CCFL Compared to NTSC Standard


Source : Luxeon

Advantage of LED Backlight vs CCFL

Vivid colors from saturated Red, Green and Blue LED light source


Reduced Motion Artifacts using fast-switching LEDs instead of CCFL being constantly turned ON

Backlight Constant-On Backlight BlinkingWith Fast-Switching

Advantage of LED Backlight vs. CCFL



Increased Color freedom - white light produced from frequencies close to the 3 primary colors

• Sony’s QUALIA 005 LCD TV offers 105% of NTSC spec.

• NM Visual’s LCD monitor supports the Adobe RGB standard

• Medical imaging LCD panel developed by NEC adjusted to match X-ray film background color


Thinner and Lighter Backlight

No Inverter Needed

Thin Bezel

Source : www.sony


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LED Backlight ModuleLED Backlight Module


LED

LENS

DiffuserLGP

Reflector

In an LCD LED backlight module, strip(s) of RBG or White LEDs are used as light source instead of CCFL tube(s).

In general, there are 2 types of LED backlight designs: edge-emitting and direct-emitting. The diagram shown below is a design of edge-light type LCD monitor backlight module using a strip of LEDs instead of CCFL as light source (OSRAM 6-lead MULTILED LRTBG6SG RBG LEDs)

LED Backlight Module


LED light bar for edge-emitting BLU

The edge-emitting BLU is widely adapted for small screen size displays such as portable media devices, PDAs and mobile phones and is already good enough for the display system.

For panel screen size < 30”, the cost of BLU is more sensitive such that CCFL is still playing an important role. The optic design in this system includes the light guide and diffuser. This enables the focused light source to deliver evenly over the panel area.

Edge-Emitting LED BLU


Direct-Emitting LED BLU

The challenge becomes greater as the screen size gets biggerFor larger screen size, the Direct-Emitting LED BLU will be

considered because of the better uniformity and display quality.


March 18, 04: NEC-Mitsubishi debuts 21.3”LED-backlighted monitor

October 5, 04: Sony debuts 23” WUXGA monitor

August 19, 2004: Sony debuts 40” & 46”Qualia 005 LCD TV

January 6, 2005: Samsung 46” LCD TV

LED light-bar used inside the BLU

Products or Proto-types Shown Using LED BLUs


Largest LCD TV with RGB LED BLU

Samsung at CeBIT 2006 demonstrated world’s largest 82” HD 1920x1080p 16:9 contrast ratio 7000:1 dynamic contrast 500 units(cd/m2) brightness 0.5KW TFT LCD TV with RGB LED backlight technology

http://www.reuters.co.in/locales/c_newsArticle.jsp;:422bf95c:1cf68db6d5ea3d6?type=technologyNews&localeKey=en_IN&storyID=7821226


46” LED BLU Demonstration in China Freescale Technology Forum 2006

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Concerns With Using LEDs for Backlight


LED color decay & stability over time & temperature:• Relative LED Light Output at Different Ambient Temperature

Issues of Current LED Backlight Module Design


LED color decay & stability over time• Luminance Deterioration vs. Emission Time

Issues of Current LED Backlight Module Design

Source : Nikkei Electronics Asia 2005 03


Source : Nikkei Electronics Asia 2005 03

Tight packing of the RGB LEDs produces better lighting mixing which enhances color uniformity, but concentrated heat sources degrade the thermal radiation performance

Loose packing improves cooling but color variation becomes more pronounced.

Issues of Current LED Backlight Module DesignIssues of Current LED Backlight Module Design

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Freescale Solution


Target Achievement by LED solution

RoHS compliance• RoHS at EU starting Jul 2006 requested CCFL must

contain less than 5mg of mercury per lamp, under one of the exemptions listed in the Annex to RoHS Directive

Color gamut >100% NTSC Total system power consumption should be similar to the

one using CCFL BLU that is in the range of 100 to 150W The color shift requirement is <0.5%


Differentiation – LED Backlight Experience / Total System Solution

Experience team based in HKG and building complete LED backlight systems ,

• Built TV and monitor demo systems for customers in the industry

• Have own color management algorithms/ software (patents Filed !)

Capable to offer all building blocks including analog driver with power management and controller with software

Color management solution implemented in 46” LCD TV

15” Monitors using CCFL & using LED with FSL color management solution

20” LCD Monitor using LED with FSL color management solution


Differentiation – Process Technology and System Architecture

SMARTMOS™ is Freescale industry leading, proprietary process technology which provides the highly integrated analog with digital control

We have the patented system architecture fulfill the needs of the latest LED BLU Technology


Issues in existing LED solution

Expensive power control hardware for each LED string High field failure due to the overheat problem Poor PWM control algorithm – edge aligned No individual thermal feedback for each string Hardware complexity increase for more LED units

employed in the larger panel


Advantages of FSL SolutionAll building blocks from one manufacturer : Intelligent LED driver with

power management and logic control, MCU and Software – Total System Solution

Scalable, intelligent architecture from small to large LCD panels for notebook, monitor and TV applications

Effective System Architecture to implement local dimming, and dynamic contrast control

The LED aging and thermal compensation are the consideration factors to keep the good display uniformity

Compensate the linearity of the LED driverPatented system architecture to address the need of the Multi-zone control

requirement in the latest advanced BLU


Freescale LCD Backlight Solution

PWM

Intelligent

Driver

ADC channel

Timers

FreescaleMCUCore

PanelTemperature

ColorSensorInputs

Flash / RAMGPIO

SCI/SPI

LCD PanelAnd

Back Light Module

OSCINTDBG

Safety Detection

Interface toLCD ControllerFor adjusting color temp,Brightness,

Sync

IntensityUniformityfeedback


FSL’s Patent on intelligent LCD Backlight system

Dynamic sensing and control of a set of parameters (temp, drivers non-linearity, LED binning, local area luminosity).

BLU controlBLU control

Local tempLocal tempLED binning LED binning parametersparameters

Drivers nonDrivers non--linearitylinearityLocal dimmingLocal dimming

CoefficientCoefficient

LED driverLED driver


Freescale Proprietary Process: SMARTMOS™

SMARTMOS™ is Freescale industry leading, proprietary process technology

Designed for high level integration including power, analog and logic

• Low RDS-on FETs for compact power devices• Down to .25µm (.18µm next gen.) for compact digital/ logic design• High voltage support up to 80V (120V next gen.)• Trench isolation to reduce cross talk for high level integration devices• Thick metal for high current capability in small area• High temperature operation up to 175°C• Latch-up immunity

= high integration, low cost, integrated solutions!


FSL LED Driver Product Highlights

Freescale developing complete LED backlight driver chip set • Scalable intelligent architecture for various panel size• Modular solution = scalable feature set

Low cost simple feature rich advanced• Supports multiple channels of LEDs for better system cost• High efficiency drive scheme to reduce heat

Auto adjusted output voltageLow drop-out Constant Current Drivers

• Smart PWM scheme for reduced EMI and low in-rush current • Optical closed loop operation is possible• Segmented backlight architecture for relaxed binning of LEDs• Supports dynamic backlight and zoned backlight control


Advantages of FSL System Solution

Scalability

Power Consumption

Intelligent PWM

Zoned backlight


Color Management Controller


LCD TV main LCD TV main Processor via I2CProcessor via I2C

Color sensor inputsColor sensor inputs

PanelPanelTemperatureTemperature

PWMsPWMsFor For

LED ControlLED Control(Can be 1set ,(Can be 1set ,

or 2 sets)or 2 sets)

LED Operation DetectionLED Operation Detection

SyncSyncInputInput

Over CurrentOver CurrentDetectionDetection

Over Voltage Over Voltage DetectionDetection

UARTUART

BDMBDMinterfaceinterface

Package : 44/64LQFPPackage : 44/64LQFP

VSSVSS VDDVDD VSSaVSSa VDDaVDDa

60K Flash

Proposed BLU Control MCU – 68HC9S08AW60


Calculation of PWM ratio for RGB LEDs

(fR/G/B) is the fraction of R, G, B for color mixing

(Xw, Yw) is the desired white point color space

(XR/G/B, YR/G/B) are the R/G/B LED color space as selected from particular LED binning

( fR/G/B ) = F( XR/G/B,YR/G/B ) F( Xw, Yw )


ColorManagement

Controller+

MCUBased

IntelligentDriver

Desired white balance point input from the system (user)

Actual result measured from the panel

Color SensorInput

LCD BLU

Color Analyzer

Calibration Setup


Using low cost Flash-based MCU to handle different LED binning by profiles which can be pre-stored in the on-chip NVM

Using R-G-B LED set to generate the white light, and MCU can perform the right color mixing (Color space coordinate) by usingstandard formula

Minimize LED binning problem with MCU


Summary

System development in Hong Kong and patent already filed

Freescale provides a total system LED BLU solution with color management controller, DC2DC and LED driver in a patented system architecture for LCD TV and monitor

Advanced process enables differentiation from other solutions

Local dimming and dynamic contrast control can be implemented by the system architecture

The LED aging, thermal compensation and linearity of LED driver had been considered to keep the good display uniformity

TM

Documents

Lighting Solution (HBLED General Lighting and CCFL and LED …read.pudn.com/downloads100/doc/project/410449/ccfl.pdf · CCFL is the short form of Cold Cathode Florescence Lamp CCFL