Input Voltage Range 4.7V 5.5V Full-Bridge Topology High Efficiency Bui

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Input Voltage Range 4.7V 5.5V Full-Bridge Topology High Efficiency Bui

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BACKLIGHT INVERTER CONTROLLER
Input Voltage Range 4.7V 5.5V Full-Bridge Topology High Efficiency Built-in Analog Burst Dimming Function Open Lamp Protection Over Voltage Protection Soft Start Synchronizable Switching Frequency with External Signal Supprts Multiple CCFLs Rail-to-Rail Totem Pole Output Power CMOS Process
KIC3812FT
CMOS Linear Integrated Circuits
MILLIMETERS
0.15 0.25 0.055 0.05 0.889 1.200 0.15 0.65 0.15 0.09 0.20
Application
Cold Cathode Fluorescent Lamps System Personal Digital Assistans Notebook Computer Monitor ATM/Financial Terminal Video Phone/Door Phone
TSSOP-20
BLOCK DIAGRAM
TIMER
Output Driver Over Voltage Protection
NOUT1 POUT1
From Oscillator Clock Oscillator
Hysteresis Comparator
2.5V
Power Hysteresis Comparator Signal Control
PGND BPWM
AGND VREF
Reference
Burst
Frequency Oscillator& Dimming Control
Oscillator Sync Comparator Open Lamp Protection
SYNC
1.25V 2.5V
1.25V
Comparator Output Driver
POUT2 NOUT2
2006.
Revision
KIC3812FT
Description
Symbol TIMER AGND VREF SYNC NOUT2 POUT2 BPWM PGND POUT1 NOUT1 Capacitor CCFL ignition duration Over voltage protection Enable input Soft-start capacitor Voltage source Signal ground Reference voltage output typical Synchronization input Inverting input error amplifier Compensation output error amplifier N_MOSFET drive output P_MOSFET drive output Burst-frequency signal burst-mode dimming control Input analog signal dimming control Triangular wave burst-mode dimming; frequency Power ground Timing resistor operating frequency Timing capacitor P_MOSFET drive output N_MOSFET drive output Description
Maximum Rating (Ta=25
Power Supply Voltage PGND,AGND Power Dissipation @Ta=25 Operating Temp. Storage Temp.
unless otherwise noted.)
Rating SYMBOL PGND,AGND Topr Tstg Limits -20~85 -55~150 UNIT
Recommended Operationg Conditions
Rating Power Supply Voltage Oscillation Frequency Timming Resistor SYMBOL Limits 4.7~5.5 50~300 60~180 UNIT
2006.
Revision
KIC3812FT
ELECTRICAL CHARACTERISTICS VDD=5V, VENA=1.5V, Ta=25
Parameter Reference Voltage Nominal Voltage Line Regulation Load Regulation Main Frequency Oscillator(1) Initial Accuracy High Voltage Voltage Burst Frequency Oscillator Initial Accuracy High Voltage Voltage Burst Frequency Duty Cycle Range Error Amplifier
Symbol
Test Conditions
Unit
VREF Reg.Line
IREF =4.7V 5.5V
2.45
2.55
Reg.Load IREF
CT=120 ,RT=82
fBCT
=8.2
VDIMH VDIML
100%, RBPWM=10 RBPWM=10
Input Voltage range Open Loop Voltage gain Unity Gain Bandwich Power Supply rejection Threshold Output Output VEN(OFF) VEN(ON) VOVP VOLP VSST VTIMER=2.5V VSST VTIMER=2.5V PSRR
Over Voltage Protection Open Lamp Protection Analog Dimming Dimming Range Supply
BPWM=0V
Standby Current Supply Current after Protection Supply Current Timer Current Current
IDDP ITIMER ISST
VOVP 2.5V, VDIM=1.3V, VOVP 2.5V VOVP 1.5V
2006.
Revision
KIC3812FT
ELECTRICAL CHARACTERISTICS (Continued) VDD=5V, VENA=1.5V, Ta=25
Parameter Output
Symbol
Test Conditions
Unit
PMOS Drive Output Voltage
NMOS Drive Output Voltage Rising Time Falling Time Overlap Time Delay Time Duty Cycle Note RBPWM from BPWM AGND.
Note lamp oscillotor frequency half main frequency. Note Only verified simulation. 100% tested. Note CN1, from NOUT1, NOUT2 PGND. CP1, from POUT1, POUT2
APPLICATION CIRCUIT
220u 12Vdc
TIMER NOUT1 POUT1
1.5Vdc
120p
PGND
8.2n
5Vdc
CCFL1
AGND VREF SYNC
BPWM POUT2 NOUT2
200K 100K Vdim 0Vdc
8.2n
KIC3812FT
100K 100n
2006.
Revision
KIC3812FT
FUNCTION DESCRIPTION UVLO
under-voltage-lock-out circuit turns output driver when supply voltage drops low. UVLO circuit turns control circuit when exceeds 4.2V.
1000
[kHz]
1.08 CT[pF]
RT[k
Main Oscillator Frequency
provides function turn output without shut down supply voltage. threshold 0.7V, 1.2V. (kHz)
120k
SYNC
SYNC used frequency synchronization. operating frequency synchronized with external signal. external resistor AGND should used operate SYNC stably. threshold voltage SYNC 1.25V.
1000
(pF)
Error Amplifier
CCFL current regulated through error amplifier. Error amplifier output (CMP) voltage triangular wave (CT) make pulses. non-inverting reference 1.25V nominal.
Burst-mode Frequency burst-mode frequency determined resistor capacitor connected pin. frequency calculated
Soft-start
soft-start function provided with capacitor connected pin. provides rate rise pulse width where switches turned capacitor connected
1000
[Hz]
0.131 BCT[nF] RT[k]
Burst Mode Frequency
~0.4 second period striking lamp.
ISST [uA]
fBCT (Hz)
T[s]
CSST [uF]
120k
Analog Burst-mode Dimming
dimming control method determined value BPWM pin. threshold BPWM 0.5V. value BPWM less than 0.5V, dimming control method analog dimming. analog dimming range value BPWM more than 0.5V, dimming control method burstmode dimming. compare input with triangular wave(BCT) makes pulses Burst-mode Dimming. BPWM pulled make dark portion CCFL output burst floating state make bright portion. less than 0.5V input VDIM will obtain 100% brightness. Frequency Operation Frequency resistor capacitor determine main frequency main frequency calculated below equation:
1000
(nF)
Protection
Open Lamp Protection Open lamp protection ignition time provided through OVP, TIMER ensure rated voltage achieved required timing satisfied. time that TIMER capacitor charges 2.5V long than CCFL ignition time, prevent over-operating protection circuit. When output voltage reaches threshold, commands controller maintain current driving level. This ensures that output gets sufficient striking voltage while operating power transformer safely. threshold nominal.
2006.
Revision
KIC3812FT
TRANSIENT RESPONSE
Time(s)
-1.0
Time(s)
-1.0
Time(s) Timer
-1.0
Time(s)
100u 200u 300u 400u 500u
FULL-BRIDGE SIGNAL CONTROL
POUT1
PWMOUT
NOUT1
POUT2
NOUT2
POUT1
Delay
Overlap
Delay
2006.
Revision
KIC3812FT
TRANSFORMER DESIGN
-VIN
LAMP
FULL-BRIDGE POWER STAGE
Transformer Turns Ratio Calculation required turns ratio involves estimation critical factors. Estimating Minimum Primary Voltage. minimum primary voltage obtained from value supply voltage.
From Faraday's law, required number secondary turns would
Nsecondary
Vsecondary
where, magnetic flux density. Required Number Primary Turns
Estimating Maximum Secondary Voltage. secondary composed voltage divide capacitor lamp parasitic capacitor. voltage across secondary calculated below equation:
From turns ratio number secondary turns
Nprimary=
Determination Wire Gauge
Nsecondary
Wire gauge done acceptable current density.
Vsecondary(rms)
Transformer turns ratio
From assumed current density (500cmil) current that flows through wires, required Circular Mils
Vsecondary Vprimary
Cmils CDLim
IRMS
From table, pick wire-gauge that would limit. Using selected wire diameter bobbin information, determine this wire gauge will space allotted. (when space factor[SF] accounted for)
Required Number Secondary Turns From core constant provided core manufacturer, will need effective core cross sectional area(Ae).
2006.
Revision

Input Voltage Range 4.7V 5.5V Full-Bridge Topology High Efficiency Bui

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