CCFL Backlight Controller AME9001 controller provides cost effici

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CCFL Backlight Controller AME9001 controller provides cost effici

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AME9001
CCFL Backlight Controller
AME9001 controller provides cost efficient means drive single multiple cold cathode fluorescent lamps (CCFL). Specifically AME9001 drives external MOSFETs that, turn, drive wirewound transformer that coupled CCFL. AME9001 includes features such soft start, duty cycle dimming control, fault detection. designed work with input voltages from 24V. When disabled circuit goes into zero current mode. applications that piezoelectric transformer please look AME9000.
Configuration
AME9001
AME9001 24PIN QSOP
VREF RDELTA FAULTB 10.CSCOMP 11.CSDET 12.NC OUTC OUTAPB OUTA VBATT VDD1 COMP BRIGHT
Features
Small package: QSOP Drives multiple tubes Automatically checks common fault conditions 7.0V Vbatt component count 3.5mA <1uA shutdown mode
Controller
System Block Diagram
External Components CCFL Array
Applications
Notebook computers LCD/TFT displays
9001
LIGHT
Resistors Capacitors
AME9001
CCFL Backlight Controller
Description
Name
VREF
Description
Reference. Compensation point 3.4V internal voltage reference. Must have bypass capacitor connected here VSS. Chip enable. When (<0.4V) chip into current (~0uA) shutdown mode. Blanking interval ramp. During first cycle this sources During subsequent cycles sources 150m This primarily used provide "blanking interval" beginning every dimming cycle temporarily disable fault protection circuitry. (See application notes.) resistor connected from this VBATT modulates switching frequency function battery voltage. VSS. resistor from this sets minimum frequency VCO. voltage this 1.5V Negative supply. Connect system ground. Over voltage protection input. Indirectly senses voltage secondary transformer through resistor capacitor) divider. will immediately turn circuit voltage over will also turn chip voltage less than 250mV successive clock cycles after voltage risen above (SSC>3V). Negative input auxiliary error amplifier(EA2). this application normally shorted CSCOMP Output auxiliary error amplifier(EA2). this application auxiliary error unity gain configuration voltage CSCOMP =1.25V long 1.25V. Otherwise CSCOMP clamped voltage SSC. Current sense detect. Connect this CCFL current sense resistor divider. this below 250mV consecutive clock cycles after then circuit will shutdown. Must float. Drives external NFETs, opposite phase OUTAPB. Drives external NFETs, opposite phase OUTC. Drives high side PFET. Battery input. This positive supply OUTA driver. Must tied VDD. Regulated supply input. Sets dimming cycle frequency. Usually about 100Hz. Negative input voltage control loop error amplifier. Output voltage control loop error amplifier. Brightness control input. voltage this controls duty cycle dimming cycle. This compared ramp pin. Soft start ramp voltage control loop. (20uA source current.) Drives base external transistor used LDO.
RDELTA FAULTB
CSCOMP
CSDET OUTC OUTAPB OUTA VBATT VDD1 COMP BRIGHT
AME9001
CCFL Backlight Controller
Ordering Information
Part Number
AME9001AETH
Marking
AME9001AETH xxxxxxxxHN yyww
Output Voltage
Package
QSOP-24
Operating Temp. Range
40oC 85oC
xxxxxxxx Internal code
Absolute Maximum Ratings
Parameter
Battery Voltage (VBATT) Classification
Maximum
Unit
Caution: Stress above listed absolute maximum rating cause permanent damage device
Recommended Operating Conditions
Parameter
Battery Voltage (VBATT) Ambient Temperature Range Junction Temperature
Rating
Unit
Thermal Information
Parameter
Thermal Resistance (QSOP Maximum Junction Temperature Maximum Lead Temperature Sec)
Maximum
Unit
AME9001
CCFL Backlight Controller
Electrical Specifications
25OC unless otherwise noted, VBATT 15V, 0.01uF,
Parameter supply (VSUPPLY) Output voltage Line regulation Load regulation Temperature drift 3.4V reference (VREF) Initial voltage Line regulation Temperature drift VREF REFLINE REFTC Vbatt 15V, Iref Vbatt -10C 3.25 -0.1 3.525 ppm/C VDDLINE DDLOAD VDDTC 7<Vbatt<24 Vbatt=7V, Iload 25mA -10C -0.5 -0.2 5.15 5.35 Symbol Test Condition Units
Brightness oscillator (CT1, BRIGHT) Ramp amplitude Frequency Line regulation Temperature drift Comparator offset oscillator (RT2, RDELTA) Initial frequency Line regulation Temperature drift pullin range FVCO(OUTA) LINEVCO TCVCO PULLVCO Vbatt -10C -0.8 +-0.5 RT2/(RDELTA VCT1 FCT1 LINECT1 TCCT1 VOSCT1 Vbatt -10C -0.5 =+-3
Error amplifiers (FB, COMP, CSCOMP) Offset voltage, Vref Input bias current Input offset current Open loop gain Unity gain frequency Output high voltage (comp) Output voltage Output high voltage (cscomp) ISOURCE 50uA ISINK 500uA ISOURCE 50uA 4.77 3.39
AME9001
CCFL Backlight Controller
Electrical Specifications(contd.)
25OC unless otherwise noted, VBATT 15V, CT1=0.01uF,
Parameter Output (OUTA) Peak current Output Voltage Output High Voltage Other outputs (OUTAPB, OUTC) Peak current Output Voltage Output High Voltage Soft start clamps (SSC, SSV) Initial current Normal current current Other parameters high threshold threshold high threshold threshold CSDET threshold Average supply current Average current HIGH CELOW OVPHI OVPLO VTHCS IBATT IOFF gate current application 3.55 ISSCINIT ISSC ISSV IPEAKBC ISINK 10mA ISOURCE 10mA 0.25 IPEAKA 0.2mA -5mA 14.4 10.8 Symbol Test Condition Units
AME9001
CCFL Backlight Controller
Block Diagram
Figure AME9001 Block Diagram
VREF 3.4V REFERENCE CHIP ENABLE LOGIC
150uA
VREF VDDOK
5.0V
CLAMP1
1000pF
22nF Vbatt 1.2Meg
BRIGHT BRIGHTNESS CONTROL VOLTAGE
RDELTA
2.5V
F_RANGE RAMP
COMP 47nF
F_MIN
0.1µF FAULTB
VCO_CONTROL
SLOW RAMP GEN.
0.01uF
FIRST
4.7uF
VDDOK
FAULT CHOP LOGIC NORM
CSDET
VDD1
VBATT
10uF
CSCOMP
DUTY OUTA
OUTA
1.25V
CHOP
OUTAPB
CSDET
OUTPUT DRIVER
OUTC
OUTAPB Q3-1 Q3-2
OUTC
AME9001
CCFL Backlight Controller
Application Schematic
Figure Single Tube Application Schematic Vbatt 24V) (Note, disabled this drawing)
BATTERY 1Meg 2N3906 3.9K
BRIGHT SI3457DV
22nF 0.1uF 0.1µF
AME9001 VREF RDELTA FAULT CSCOMP CSDET BRIGHT COMP VDD1 VBATT OUTA OUTAPB OUTC
47nF 30.1K 100K
49.9
1000pF 0.01uF 10uF 0.1uF
IRF7341
Bill Materials
Part Value 1Meg 49.9k 1.2Meg 30.1k 3.9k 100k 2N3906 Si3457DV IRF7341 Rating 1/16 watt 1/16 watt 1/16 watt 1/16 watt 1/16 watt 1/16 watt watt 1/16 watt 1/16 watt 1/16 watt 1/16 watt 1/16 watt pot. Tolerance Part Value 0.1uF 1.0uF 22nF 0.01uF 10uF 0.1uF 4.7uF 47nF 1.0uF 0.1uF 1N914 1N914 1N914 1N914 1N914 20:20:2200 Rating Tolerance
AME9001
CCFL Backlight Controller
does not. Referring Figures NMOS transistors Q3-1 Q3-2 driven phase with duty cycle signal indicated waveforms Figure frequency NMOS drive signals will frequency which CCFL driven. PMOS transistor, driven with pulse width modulated signal (PWM) twice frequency NMOS drive signals. other words, PMOS transistor turned once every time each NMOS transistor this case, when NMOS transistor Q3-1 PMOS transistor both then NMOS transistor Q3-2 off, side primary coil connected NMOS transistor Q3-1 driven ground centertap transformer primary driven battery voltage. other side primary coil connected NMOS transistor Q3-2 (now "off") driven twice battery voltage (because each winding primary equal number turns). Current ramps side primary connected Q3-1 (the "on" transistor), transferring power secondary coil transformer. energy transferred from primary excites tank circuit formed transformer leakage inductance parasitic capacitances that exist transformer secondary. parasitic capacitances come from capacitance transformer secondary itself, wiring capacitances, well parasitic capacitance CCFL. Some applications actually small amount parallel capacitance (~10pF) output transformer order dominate parasitic capacitive elements. When PMOS, turned off, voltage transformer centertap returns ground does drain NMOS transistor Q3-2 (the drain Q3-2 twice battery voltage). Halfway through cycle, NMOS transistor Q3-1 (that turns NMOS transistor Q3-2 (that off) turns this point, PMOS transistor turns again, allowing current ramp side primary that previously current. Energy primary winding transferred secondary winding stored again leakage inductance Lleak, this time with opposite polarity. current alternately goes through primary winding then other. duty cycle PMOS transistor controls amount power transferred from primary winding secondary winding transformer. Note that CCFL circuit work with PMOS transistor constantly (i.e. duty cycle 100%), although power would unregulated this case.
Application Notes
Overview goal AME9001 application circuit drive CCFL (cold cathode fluorescent lamp) with high voltage sine wave order produce efficient cost effective light source. most common application this will backlight either notebook computer display, flat panel display, personal digital assistant (PDA). CCFL tubes used these applications usually glass rods about foot long 0.125"-0.25" diameter. Typically they require sine wave 600V they current several milliamperes. However, starting striking) voltage high 2000V. start tube looks like open circuit, after plasma been created impedance drops current starts flow. characteristic these tubes highly non-linear. Traditionally high voltage required CCFL operation been developed using some sort transformerLC tank circuit combination driven several small power mosfets. AME9001 application uses external PMOS, external NMOS high turns ratio transformer with centertapped primary. Lamp dimming achieved turning lamp rate faster than human detect. These "on-off" cycles known dimming cycles. Steady State Circuit Operation Figure (and shows PMOS driving center primary gate drive pulse width modulated (PWM) signal that controls current into transformer primary extension, controls current CCFL. gate drive signal drives battery voltage down volts below Vbatt that logic level transistors used without their gates being damaged. internal clamp prevents gate drive (OUTA) from driving lower than Vbatt-7.5V. NMOS transistors Q3-1 Q3-2 alternately connect outside nodes transformer primary VSS. These transistors driven duty cycle square wave one-half frequency drive signal applied gate Figure illustrates some ideal gate drive waveforms CCFL application. Figure detailed views power section from Figures Figure transformer parasitic elements added while Figure
AME9001
Figure Idealized Gate Drive Waveforms
CCFL Backlight Controller
Gate
(OUTA)
VBATT VBATT- 7.5V
Q3-1 Gate
(OUTAPB)
Q3-2 Gate
(OUTC)
Figure Power Stage Single Tube Components
(Same component designations used Figures
Figure Power Stage Single Tube Components with parasitic elements
(Same component designations used Figures
OUTA 0-100% Vbatt Vbatt-7.5V fosc
VBATT
OUTA 0-100% Vbatt Vbatt-7.5V fosc
VBATT
OUTAPB D=50% fosc/2
Q3-1
Q3-2
OUTC D=50% fosc/2
OUTAPB D=50% fosc/2
Q3-1
Q3-2
OUTC D=50% fosc/2
leak
Signals OUTC OUTAPB inverse each other.
Cparasitic CCFL
Signals OUTC OUTAPB inverse each other.
CCFL
Control Circuitry R9+R10
Control Circuitry
R9+R10
AME9001
Figures illustrates various oscilloscope waveforms generated CCFL circuit operation. These figures show that duty cycle gate drive decreases battery voltage increases from would expect order maintain same output power). first three traces Figures show gate drive waveforms transistors Q3-1, Q3-2, respectively. mentioned before, gate drive waveform transistor drives battery voltage down only approximately below battery voltage. fourth trace Figures 6,7) shows voltage centertap primary winding also drain PMOS transistor, Q2). This waveform essentially ground battery voltage pulse varying duty cycle. When centertap primary driven high, current increases through PMOS transistor, indicated sixth trace down from top. region drain current equal opposite drain current Q3-1 since gate Q3-1 high Q3-1 region drain current will equal opposite drain current Q3-2 (not shown). region when PMOS transistor switched off, current through this transistor, after initial sharp drop, ramps back down towards zero. Figures fifth trace down from shows drain voltage Q3-1. (The trace NMOS transistor Q3-2, shown, would identical, shifted time half period.) seventh trace down from shows current through NMOS transistor Q3-1, which equal current PMOS transistor portion time that PMOS transistor conducting (see region example). current ramps primary winding, energy transferred secondary winding stored leakage inductance Lleak (and parasitic capacitance secondary winding). current NMOS transistor close zero when that NMOS transistor turned that means that CCFL circuit being driven close resonant frequency. circuit being driven from resonant point then there will large residual currents transistors when they turned causing large ringing, lower efficiency more stress components. called "soft switching" achieved when drain current zero while being turned off. driving frequency transformer parameters should chosen that soft switching occurs. Once PMOS transistor completes on/off cycle, repeated again with alternate NMOS transistor
CCFL Backlight Controller
conducting. This complementary operation produces symmetric, approximately sinusoidal waveform input CCFL load, shown bottom trace Figures operation CCFL circuit divided into regions III, shown Figures Figure shows equivalent transformer load circuit model region During region primary windings connected across battery, current that winding increases energy coupled across secondary. current flows other winding because NMOS turned body diode reverse biased. drain that NMOS stays twice battery voltage because both primary windings have same number turns battery voltage forced across other primary winding. Figure shows equivalent transformer load circuit model region During region battery disconnected from primary winding. this configuration, current flows through both primary windings. current decreases very quickly first then ramps down zero rate that slower than current ramped initial drop almost instantaneous change inductance when current flow shifts from portion primary winding both portions primary. Figure shows equivalent transformer load circuit model region III. During region III, primary winding opposite from used region connected across battery, increasing current that primary winding direction opposite that region Energy coupled across secondary region with opposite polarity. current flows undriven winding because NMOS turned body diode reverse biased. drain that NMOS stays twice battery voltage because both primary windings have same number turns battery voltage forced other primary. Region effectively, inverse region Figure shows equivalent transformer load circuit model region During region battery disconnected from primary winding. this configuration, current flows through both primary windings with opposite polarity that region current decreases very quickly first then ramps down zero rate that slower than current ramped Once again, initial drop effective change inductance when current flow shifts from portion primary winding both portions primary. Region effectively inverse region
AME9001
Figure Typical Waveforms VBATT=9V
CCFL Backlight Controller
VBATT=9V Gate
(OUTA)
1.5V VBATT VBATT IMAX IMAX
Q3-1 Gate
(OUTAPB)
Q3-2 Gate
(OUTC)
Center
DRAIN)
Q3-1 Drain IDQ2
IDQ3-1 ILAMP
Region Region Region Region
Figure Typical Waveforms VBATT=21V
VBATT=21V Gate
(OUTA)
Q3-1 Gate
(OUTAPB)
13.5V VBATT VBATT
Q3-2 Gate
(OUTC)
Center
DRAIN)
Q3-1 Drain
IDQ2 IDQ3-1
IMAX IMAX
ILAMP
Region
Region
Region
Region
AME9001
Figure 8-1. Region
ILEAK
CCFL Backlight Controller
Figure 8-2. Region
ILEAK
Cparasitic
Load
Cparasitic
Load
Figure 8-3. Region
ILEAK Cparasitic
Load
Figure 8-4. Region
ILEAK
Cparasitic
Load
Figure Steady State Dimming Waveforms (1st Cycle Show)
BRIGHT 0.5V Under voltage Under current Faults Over voltage Faults
Ignore
Respond
Ignore
Respond
Always Respond Over voltage Faults
Tube Current (time scale)
AME9001
Driving CCFL Unlike other conventional schemes driving CCFLs secondary winding AME9001 method designed look like voltage source CCFL lamp. circuit acts more like current source power source). circuit will increase duty cycle thereby dumping more more energy across secondary tank circuit until CCFL tube current achieves regulation various fault conditions met. There special "striking period" necessary with some other schemes. When circuit starts driving transformer there initially struck CCFL. CCFL load looks like open circuit. voltage across CCFL will increase with each successive cycle. events then happen: inside CCFL will ionize, voltage across CCFL will drop, current through CCFL will increase, stable steady state operating point will reached. three fault conditions will shutting down circuit: CCFL tube voltage continues rise until higher than 3.5V which point circuit will shut down. CCFL voltage fails rise high enough keep undervoltage portion from tripping. CCFL current fails rise high enough keep undercurrent threshold CSDET from tripping. Note that condition time while AME9001 enabled. Condition only after crossed four successive undervoltage events occur row. pulled everytime lamp turned off, whether dimming cycle, user shutdown fault occurrence. ramps slowly depending size capacitor connected pin. period time when fault checks disabled called "blanking" time. blanking time occurs from time starts ramp until reaches Figure some idealized waveforms illustrating behavior just described. Control Algorithm There major control blocks (loops) within first loop controls duty cycle driving waveform. senses CCFL current (Figure resistor R10) rectifies integrates against internal
CCFL Backlight Controller
reference adjusts duty cycle obtain desired power. This loop uses error amplifier whose negative input whose output COMP. positive input connected 2.5V reference. External components, time constant integrator, EA1. order slow response integrator increase value product C8). second control block adjusts brightness turning lamp varying duty cycles. Each time lamp turns referred "dimming cycle". each dimming cycle pulled low, this forces COMP well clamping action Clamp1 shown Figure beginning dimming cycle COMP tries increase quickly clamped voltage SSV(softstart voltage) pin. capacitor (C8, Figure which discharged every dimming cycle, sets slew rate voltage pin, hence also maximum positive slew rate COMP pin. ["Dimming cycle" explained more fully below] BRIGHT pins user-provided voltage BRIGHT compared with ramp voltage (See Figure 10). voltage BRIGHT increases duty cycle dimming cycle (and brightness CCFL) increase. frequency dimming cycles value capacitor Figure also proportional current resistor Setting equal 0.01uF equal 47.5k yields dimming cycle frequency approximately 125Hz. frequency should vary inversely with value according relation: Frequency(Hz) 1/[17 brightness also controlled using variable resistor place (See Figure 11). this case BRIGHT should pulled that CCFL remains constantly. This method lead flicker intensities easy implement. Harmonic distortion also increase since duty cycle waveform gate will vary greatly with brightness. When using burst brightness control duty cycle driving waveforms should vary because CCFL running 100% power turned off. long battery voltage does change duty cycle driving waveform also does change greatly. This means that harmonic distortion minimized optimizing frequency transformer characteristics particular duty cycle rather than large range duty cycle.
AME9001
Figure Duty Cycle Dimming
CCFL Backlight Controller
Outside Chip
Inside Chip
BRIGHT
CHOP CHOP causes CCFL turn periodically.
Brightness control voltage
500mV
Figure Alternative Brightness Control
Inside Chip
Outside Chip
This method disables duty cycle dimming BRIGHT CHOP Always Maximum current= R1//(2R+R) COMP 2.5V Fault Control Logic 250mV CSDET Minimum current= (R1+R2)//(2R+R)
Comparator
AME9001
RT2, RDELTA frequency drive signal gate determined shown Figure1. detail shown Figure user sets minimum oscillator frequency with resistor connected figures). relation Frequency (Hz) 2.8E9 (ohms) from formula that increased frequency gets smaller. other things being equal, battery voltage increases duty cycle driving waveform gate decreases. Often waveform becomes less sinusoidal duty cycle decreases. avoid this unwanted effect ensure that FETs remain "soft switching mode" application described here adjusts oscillator frequency upwards battery voltage increases. increase driving frequency desirable minimize harmonic distortion output waveform duty cycle drive signal gate decreases. Resistor controls much oscillator frequency increases function battery voltage. relationship Delta frequency (Hz) 3.44E8 (Vbatt -1.25) from formula that frequency will increase battery voltage increases. amount this increase current application (Figure connected unity gain which will provide constant 1.25V CSCOMP subsequently Vco_control Rdelta input VCO. Even though Vco_control fixed voltage frequency still modulates because current through changes battery voltage increases hence increases charging current into timing capacitor Figure thereby increasing oscillator frequency. Supply voltage pins, Most circuitry AME9001 works with exception output driver. That driver (OUTA) power (VBATT) must operate although OUTA never forced lower than volts away from VBATT pin. OUTA internally clamped approximately volts below Vbatt pin. AME9001 uses external device provide regulated supply from battery voltage (See Figure 13). battery voltage range from VBATT 24V. drives base external device, supply into chip.
CCFL Backlight Controller
4.7uF capacitor, bypasses supply ground. external supply available then external would necessary should float. When (<0.4V) chip goes into zero current state. chip puts into high impedance state which shuts lets supply collapse zero volts. When low, also immediately turns PMOS transistor off, however transistors Q3-1 Q3-2 will continue switch until collapsed 3.5V. Allowing transistors continue switch some time after turned permits energy tank circuit dissipated gradually without large voltage spikes. voltage sensed internally that switching circuitry will turn unless voltage larger than 4.5V internal reference valid. Once 4.5V threshold been reached switching circuitry will until less than 3.5V mentioned before). Output drivers (OUTA, OUTAPB, OUTC) OUTAPB OUTC pins standard CMOS driver outputs (with some added circuitry prevent shoot through current). OUTA driver quite different (See Figure 14). OUTA driver pulls VBATT (max 24V) pulls down about volts below VBATT. internally clamped within 7.5V VBATT. each transition OUTA will sink/source about 500mA 100nS. After initial 100ns burst current current scaled back 1mA(sinking) 12mA(sourcing). This technique allows fast edge transitions overall power dissipation. Fault Protection, CSDET pins AME9001 checks different fault conditions. When fault conditions then circuit latched off. Only power reset toggling will restore circuit normal operation. (See Figure schematic FAULT circuitry.) first fault condition check used detect overvoltages CCFL. Specifically, above then this fault condition detected. first fault condition always enabled, thus there blanking period, succesive faults required shutdown. second fault condition check used ensure that CCFL voltage above some certain voltage
AME9001
level cycle cycle basis. does cross 250mV threshold once during four successive clock periods then this fault will triggered. This protection disabled while ramp below such during initial start beginning every dimming cycle. ramp after power reset enabled) times slower than subsequent start ramps. This slow first ramp allows more time cold tube strike before chip senses fault shuts down. order enable first fault condition checks then must, indirectly, sense high voltage input CCFL. actual CCFL voltage must reduced using either resistor capacitor divider such that normal operation voltage higher than 250mV lower than third fault condition check used monitor CCFL current. Specifically, checks whether voltage CSDET higher than 250mV. CSDET does cross 250mV threshold once during successive clock cycles then this fault will triggered. This protection disabled while ramp below such during initial start period, beginning every subsequent dimming cycle. This fault condition used check that reasonable minimum amount current flowing tube. Please note that application circuit Figure uses resistor divider drive voltage above 250mV below That effectively disables first fault condition checks. Some applications require fault condition checks. third fault condition usually sufficient detect open circuit faults. Figure simplified schematic fault protection circuitry used AME9001. Most signals have been previously defined however some need little explanation. VDDOK signal power signal that goes high when supply (VDD) valid. CHOP signal stops operation switching circuitry once every dimming cycle burst mode brightness control. output signal, FIRST, high during first burst cycle after power turned causes source time less current than subsequent dimming cycles. NORM signal enable signal switching circuitry. When high circuit works normally. When switching circuitry stops. pins
CCFL Backlight Controller
pin's primary role define time period which fault condition (previously described) disabled. This period time called blanking interval. During initial start period after power reset just after high transition sources into external capacitor(C3). voltage ramps upwards towards VDD. blanking interval defined time during which V(SSC) Once voltage crosses blanking interval finished three fault condition checks enabled. beginning next dimming cycle pulled then allowed ramp upwards again, however during subsequent dimming cycles sources 150uA instead case first cycle. effect, different sourcing currents means that first blanking interval times long subsequent blanking intervals. This allows cold tube more time strike before shutting down undercurrent undervoltage fault. (Please figure further clarification blanking function.) (like pin) pulled ground beginning every dimming cycle then sources 20uA into external capacitor. This creates volt ramp pin. This ramp used limit duty cycle gate drive signal available OUTA pin. accomplishes duty cycle limiting clamping COMP voltage higher than voltage. Because magnitude COMP voltage proportional duty cycle signal OUTA duty cycle starts each dimming cycle zero slowly increases steady state value voltage increases. (Figure shows this operation.) This type duty cycle limiting commonly called "soft-start" operation. Soft start operation lessens overshoot start because power increases gradually rather than immediately. Unlike current sourced remains approximately 20uA during dimming cycles. Ringing leakage inductances transformer voltages drains potentially ring values substantially higher than ideal value (which twice battery voltage). application schematic figure uses snubbing circuit limit extent ringing voltage. Components C9,R8,D2 make snubbing circuit. nominal voltage common
AME9001
node approximately twice battery voltage. either drains ring above that voltage then diodes forward bias allow ringing energy charge capacitor Resistor bleeds extra ringing energy preventing voltage common node from increasing substantially higher than twice battery voltage. extra power dissipation P(dissipated) Vbatt2 example, Figure power dissipation snubber circuit with Vbatt=15V 58mW approximately total input power. value optimized particular application order minimize dissipated power. Excessive ringing usually sign that driving frequency well matched resonant characteristics tank circuit. well designed application snubber circuit will necessary. Layout Considerations switching nature this circuit high voltages that produces this application sensitive board parasitics. fact, advantages, this design that circuit uses parasitic elements application resonant components, thus eliminating need more added components. Particular care must taken with different gounding loops. best performance been obtained using "star" ground technique. star technique returns significant ground paths back center "star". Ideally would place center star directly AME9001. bypass capacitors would, ideally, connected close center star possible. schematic Figure attemps show this star ground configuration bringing ground returns back same point drawing. Separate ground returns back star especially important higher current switching paths.
CCFL Backlight Controller
AME9001
Figure Detail
CCFL Backlight Controller
Vco_Control
I_in
RDELTA 1.25V
VBATT
50:1 curent divider
I_out
1.5V
RAMP 3.0V
CSCOMP
Inside chip Outside chip
Figure Detail
Inside Chip
Outside Chip
VBATT
VDDOK
Fault Logic
VBATT
2.5V
Start
user enable circuitry 4.7µF
AME9001
Figure OUTA Driver Circuitry
Inside Chip
Vbatt
CCFL Backlight Controller
Outside Chip
BV=5V
BV=4V BV=7.5V
OUTA SIGNAL
External PMOS,
100nS
100nS
Figure Fault Logic
VDDOK
inside Chip
3.3V BRIGHT
BLANK
CHOP
250mV CSDET
RESB
COUNTER
FIRST
3.3V
RESB
NORM
COUNTER
AME9001
Application Component Description Figure shows typical application circuit single tube drive. Figure shows similar application circuit that optimized tube operation. Similar component designations used similar components both figure figure well throughout this application note. Weak pull chip enable (CE) pin. voltage will normally rise volts supply. Pull down node disable chip into zero mode. user wishes drive node with volt logic then necessary This capacitor acts de-bounce slow turn time when using pull This useful when battery power disconnected from circuit order turn circuit off, when battery reconnected chip does immediately turn which allows battery voltage stabilize before switching starts. user actively driving then capacitor necessary. This resistor connected RDELTA determines much oscillator frequency will change with battery voltage. relation, which found earlier text, Delta frequency (Hz) 3.44e8 (Vbatt-1.25) This capacitor bypasses stabilizes internal reference This capacitor determines length blanking interval beginning every dimming cycle when chip first powered every dimming cycle this capacitor discharged then allowed charge rate controlled internal current source When voltage (pin SSC) crosses volts blanking interval over fault checks enabled. charging current into (out SSC) normally 150uA very first cycle after chip enabled current only 1uA. blanking interval first cycle T(seconds) (3volts) (1e-6amps)
CCFL Backlight Controller
subsequent dimming cycles blanking interval T(seconds) (C3) (3volts) (150e-6amps) This capacitor used prevent chatter FAULTB during start sets frequency oscillator that drives FETs. relation between frequency, that found previously text, Frequency (Hz) 2.8e9/R2 yields approximately 50khz
Note: that this frequency NMOS(Q3) gate drive. PMOS(Q2) gate drive exactly twice this value.
This capacitor filters signals feeding pin. increasing user makes circuit less sensitive fast overvoltage conditions. This resistors pulls base Vbatt. Coupled with part regulator that supplies working power AME9001. When turned base pulled high through turning allowing voltage node (VSUPPLY) decay towards zero. This common transistor (2n3906 adequate) forms part linear regulator which supplies power most AME9001. This resistor, together with adjustable resistor R20, form resistor divider that divides regulated down some lower voltage. That lower voltage used drive BRIGHT which, turn, determines duty cycle dimming cycles therefore brightness lamps. user driving BRIGHT with his/her voltage source then necessary. This capacitor bypasses BRIGHT pin. noisy BRIGHT cause unwanted flicker.
AME9001
description This capacitor sets slope soft-start ramp SSV. voltage limits duty cycle gate drive signal available OUTA. voltage COMP node internally clamped node. Therefore limits fast SSV, hence, COMP increase. charging current approximately 20uA rate change voltage SSV(Volts/sec) (20e-6amps) This main battery bypass capacitor. This capacitor sets frequency dimming cycles according relation: Cycle Freq(Hz) [(17) (R2) (C4)] Note that frequency also function frequency main oscillator frequency dimming oscillator independent. This capacitor load capacitor linear regulator. such also bypasses supply should laid close AME9001 possible. This capacitor, combination with resistor determines time constant error amplifier (integrator) EA1. integrator primary loop stabilizing element circuit. general this application tolerant large range integrator time constants. Increase product slow down loop response. This diode catch negative going spikes drain This diode strictly necessary. This freewheeling diode such buck regulator. Since primary windings tightly coupled each other body diodes Q3-1 Q3-2 keep their drains clamped well drain spikes that diode catch short duration small energy. This PMOS device. modulating gate drive duty cycle power into transformer, then into load, controlled. breakdown this device must higher than highest battery voltage that application will use. peak current
CCFL Backlight Controller
load roughly twice average current load. Q3-1, Q3-2 These NMOS devices. They driven alternately with duty cycle gate drive. frequency gate drive half gate drive frequency gate drive from volts. breakdown voltage these devices must least twice highest battery voltage. Peak current roughly twice average supply current. C9,R8,D2,D3 These devices form snubber circuit that dissipate ringing energy. snubber circuit strictly necessary. fact well designed circuit should require these devices. (These elements were described more detail earlier.) sets current CCFL tube. decreases tube current goes increase tube current goes down. tube current roughly: Irms R10) also form voltage divider that drives CSDET pin. purpose voltage divider keep maximum voltage CSDET under volts under conditions. CSDET checks there current CCFL. voltage CSDET larger than 250mV once every clock cycle then AME9001 assumes there current CCFL allows operation continue. D4,D5 These diodes rectify current through CCFL provide positive voltage regulation error amplifier, EA1.
following components only used multiple tube operation:
Q4,Q5 These bipolar devices buffer gate That allows made much bigger without dissipating more power increasing cost AME9001. transistor transistor. R35,R36,D16 These devices form voltage divider rectifier combination sense higher than normal
AME9001
transformer operating voltages. This operation explained more detail below.) R38,R39,D17 R35,R36,D16 description above. diode "OR" many these divider/rectifier circuits have different transformers. Each time another double output transformer must another these resistors diode networks. This operation explained more detail next section.) Multiple Tube Operation AME9001 particularly well suited multiple tube applications. Figure17 shows power section tube application. major difference between this application single tube application addition another secondary winding transformer. primary side transformer associated FETs exactly same single tube case although FETs need resized increased current tube applications. secondaries wound that outputs CCFL opposite phase (see Figure 18). When voltage secondary output high (+600 volts) other secondary output should (-600 volts). other secondary terminals connected each other. balanced circuit voltage connection secondaries will, ideally, zero. course real application voltage connection secondaries will deviate somewhat from zero. common connection secondaries offers excellent method check high voltage fault conditions. previously mentioned, when CCFL loads balanced then voltage common connection secondaries will remain relatively compared high voltages available other terminals secondaries. However, when loads become unbalanced, would case tube broken there connection, then voltage common point secondaries will much higher than normal value. simple size resistors Figure17 such that normal operation voltage remains below volts while during abnormal operation voltage goes above volts causing system fault.
CCFL Backlight Controller
multi-tube configuration modular. Since each double transformer drive CCFLs possible construct tube solutions using basic architecture. course FETs must properly sized handle increased current. Figure19 shows tube application. this configuration common secondary connection (the node connected lamp) made with opposite transformer. this secondary current from winding first transformer should equal secondary current companion winding second transformer. case lamps driven transformers there sets common secondary nodes. Each drives resistor divider this case R35/R36 R38/R39) whose outputs diode "OR'd" together node. That either transformer that experiences overvoltage fault condition will able pull node cause system shut down. concept expanded more than four tubes. every extra tubes that need added user must more transformer, resistor divider, small diode such 1N914. Figure shows complete multi-tube architecture schematic. Analogous components have been given same numbers single tube schematic. There really very little difference between single tube configuration multi-tube version. Transistors added buffer high side drive OUTA. This necessary because PMOS devices larger current applications have larger gate drive requirements. Capacitor added node that unwanted high frequency signals couple node cause undesired shutdown. transistors sized bigger tube application would expected. peak currents much higher Vbatt bypassing capacitor must increased well. schematic shows 100uF capacitor higher values such 220uF uncommon order minimize ripple Vbatt.
AME9001
CCFL Backlight Controller
Figure Four Tube Application Schematic
BATT 2N3904
1.2Meg 1Meg
2N3906
3.9k SNUB IN914
5602
2N3906
IN914
BRIGHT
2XTRANS
2XTRANS
400k IN914 IN914
400k
Vref
0.022uF 0.1uF 0.1u 49.9k
AME9001 Vref BRIGHT RDELTA COMP FAULTB VSUPPLY DUTY VBATT CSCOMP OUTA CSDET OUTAPB CSPEAK OUTC
47nF 1000p 100k 30.1k Q3-1 IRFR3303 Q3-2 IRFR3303 IN914 IN914 OUT-1
100p
0.01uF
100uF
0.1uF
4.7uF
1N5819
AME9001
Figure Double CCFL Power Section
VBatt OUTA
CCFL Backlight Controller
OUTB
Q3-1
Q3-2
OUTC
Outside Chip
2.5V CSDET Fault Logic 250mV COMP
Inside Chip
Comparator
Figure Double transformer construction detail
voltages
Secondary
Primaries
Secondary
Large Positive (Negative) Voltage
Large Negative (Positive) Voltage
Common Core
voltages center
AME9001
Figure Four Tube Power Section
CCFL Backlight Controller
OUTA
VBatt OUTAPB
Q3-1 integrator Q3-2
CSDET
OUTC
AME9001
CCFL Backlight Controller
Package Dimension
QSOP24
View
SYMBOLS
MILLIMETERS
1.524 0.101
INCHES
0.060 0.004
1.752 0.228
0.069 0.009
1.473REF 0.203 0.203 0.177 0.177 8.559 0.304 0.279 0.254 0.228 8.737
0.058REF 0.008 0.008 0.007 0.007 0.337 0.012 0.011 0.010 0.009 0.344
Bottom View
0.838REF 5.791 3.810 0.406 6.197 3.987 1.270
0.033REF 0.228 0.150 0.016 0.244 0.157 0.050
Side View
Detail
0.254BSC 0.635BSC 1.27REF 1.27REF 0.33
0.010BSC 0.025BSC 0.050REF 0.050REF
0.013
View
Detail
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E-Mail: info@ame.com.tw
Life Support Policy: These products AME, Inc. authorized critical components life-support devices systems, without express written approval president AME, Inc. AME, Inc. reserves right make changes circuitry specifications devices advises customers obtain latest version relevant information. AME, Inc. April 2003 Document: 2023-DS9001-A
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CCFL Backlight Controller AME9001 controller provides cost effici

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