From Oscillator Clock. Hysteresis Comparator. Signal Control. Hysteresis Comparator. To Oscillator. Open Lamp. Protection 2.5V. SST CT PWM Comparator

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1 SEMICONDUCTOR TECHNICAL DATA KIC3812FT CMOS Linear Integrated Circuits LCD BACKLIGHT INVERTER CONTROLLER Input Voltage Range of 4.7V to 5.5V ZVS Full-Bridge Topology High Efficiency Built-in Analog and Burst Dimming Function Open Lamp Protection and Over Voltage Protection Soft Start Synchronizable Switching Frequency with External Signal Supprts Multiple CCFLs Rail-to-Rail Totem Pole Output Low Power CMOS Process Application Cold Cathode Fluorescent Lamps System Personal Digital Assistans Notebook Computer LCD Monitor LCD TV ATM/Financial Terminal Video Phone/Door Phone P A D G B1 B2 H T TSSOP-20 DIM A B1 B2 D G H L P T L MILLIMETERS 6.5 +_ _ _ _ _ ~ _ _ ~ 0.20 BLOCK DIAGRAM TIMER Over Voltage Protection 2V Hysteresis Comparator From Oscillator Clock Output Driver Oscillator NOUT1 POUT1 CT ENA RT SST VDD AGND V REF SYNC Power Off Reference Sync Comparator 2.5V Q To Oscillator Hysteresis Comparator R S Open Lamp Protection Signal Control Burst Frequency Oscillator& Dimming Control PGND BCT DIM BPWM 1.25V 2.5V FB CMP 1.25V SST CT PWM Comparator Output Driver POUT2 NOUT2 1/7

2 PIN Description NO Symbol I/O Description 1 TIMER I Capacitor for CCFL ignition duration 2 I Over voltage protection 3 ENA I Enable input 4 SST I Soft-start capacitor 5 VDD I Voltage source for the IC 6 AGND I Signal ground 7 V REF O Reference voltage output ; 2.5 typical 8 SYNC I Synchronization input 9 FB I Inverting input of error amplifier CMP O Compensation output of the error amplifier 11 NOUT2 O N_MOSFET drive output 12 POUT2 O P_MOSFET drive output 13 BPWM O Burst-frequency PWM signal for burst-mode dimming control 14 DIM I Input analog signal for dimming control 15 BCT I Triangular wave for burst-mode dimming; frequency 16 PGND I Power ground 17 RT I Timing resistor set operating frequency 18 CT I Timing capacitor 19 POUT1 O P_MOSFET drive output 20 NOUT1 O N_MOSFET drive output Maximum Rating (Ta=25, unless otherwise noted.) Rating SYMBOL Limits UNIT Power Supply Voltage V DD 6 V PGND,AGND P GND,A GND 0.3 V Power P D 800 Operating Temp. T opr -20~85 Storage Temp. T stg -55~150 Recommended Operationg Conditions Rating SYMBOL Limits UNIT Power Supply Voltage V DD 4.7~5.5 V Oscillation Frequency f CT 50~300 KHz Timming Resistor RT 60~180 2/7

3 ELECTRICAL CHARACTERISTICS V DD =5V, V ENA =1.5V, Ta=25 Parameter Symbol Test Conditions Min Typ Max Unit Reference Voltage Nominal Voltage V REF I REF = V Line Regulation Reg.Line V DD =4.7V to 5.5V Load Regulation Reg.Load I REF = 0.1 ~1-4 - Main Frequency Oscillator (1) Initial Accuracy f CT C T =120,RT= CT High Voltage V CT Low Voltage V Burst Frequency Oscillator Initial Accuracy f BCT BCT = Hz BCT High Voltage V BCT Low Voltage V Burst Frequency PWM (2) Duty Cycle Range V DIMH 0%, R BPWM = V V DIML 0%, R BPWM = V Error Amplifier (3) Input Voltage range V Open Loop Voltage gain G V Unity Gain Bandwich f T Power Supply rejection PSRR Threshold ENA Output Off V EN(OFF) V Output On V EN(ON) V Over Voltage Protection V V SST or V TIMER =2.5V V Open Lamp Protection V OLP V SST or V TIMER =2.5V V Analog Dimming Dimming Range BPWM=0V 0-2 V Supply (4) Standby Current I SY V EN = 0V Supply Current after Protection I DDP V = 2.5V, C N1 = C N2 = C P1 = C P2 = 2nF Supply Current I DD V DIM =1.3V, C N1 = C N2 = C P1 = C P2 = 2nF Timer Current I TIMER V = 2.5V SST Current I SST V = 1.5V /7

4 ELECTRICAL CHARACTERISTICS (Continued) V DD =5V, V ENA =1.5V, Ta=25 Parameter Symbol Test Conditions Min Typ Max Unit Output (4) PMOS Drive Output Voltage NMOS Drive Output Voltage V PH C P1 = C P2 = 2nF V V PL C P1 = C P2 = 2nF V V NH C N1 = C N2 = 2nF V V NL C N1 = C N2 = 2nF V Rising Time t R C N1 = C N2 = C P1 = C P2 = 2nF Falling Time t F C N1 = C N2 = C P1 = C P2 = 2nF Overlap Time t OL C N1 = C N2 = C P1 = C P2 = 2nF % Delay Time t DL C N1 = C N2 = C P1 = C P2 = 2nF Duty Cycle D 0-82 % Note 1 : The lamp oscillotor frequency is the half of the main frequency. Note 2 : R BPWM from BPWM to AGND. Note 3 : Only verified by simulation. Not 0% tested. Note 4 : C N1, C N2 from NOUT1, NOUT2 to PGND. C P1, C P2 from POUT1, POUT2 to VDD APPLICATION CIRCUIT C16 1u 1.5Vdc C18 1u 5Vdc C19 1u R9 50K C8 2n TIMER NOUT1 POUT1 ENA CT SST RT VDD PGND AGND BCT V REF DIM SYNC BPWM FB POUT2 CMP NOUT2 KIC3812FT C14 33n C20 120p R4 82K C22 8.2n Vdim 0Vdc ZD1 C15 33n R 200K R17 K ZD2 R14 0K M1 R18 K M2 C24 220u R21 0K TX1 C17 0n VIN 12Vdc D9 C23 p C21 8.2n D4 R CCFL1 4/7

5 FUNCTION DESCRIPTION 1) UVLO The under-voltage-lock-out circuit turns the output driver off when supply voltage drops too low. The UVLO circuit turns on the control circuit when V DD exceeds 4.2V. 2) ENA The ENA pin provides the function to turn on and off the output without shut down the supply voltage. The threshold of the ENA Off is set at 0.7V, ENA On is 1.2V. 3) SYNC The SYNC pin is used as the frequency synchronization. The operating frequency can be synchronized with an external signal. An external resistor to AGND should be used to operate SYNC pin stably. The threshold voltage of the SYNC is 1.25V. 4) Error Amplifier The CCFL current is regulated through the error amplifier. Error amplifier output (CMP) voltage and triangular wave (CT) make the PWM pulses. The non-inverting reference is at 1.25V nominal. 5) Soft-start The soft-start function is provided with a capacitor connected to SST pin. It provides a rate of rise for the pulse width where switches are turned on. A 1 capacitor connected on the SST pin can set a ~0.4 second period for striking the lamp. f CT (khz) 00 0 f [khz] = CT[pF] RT[k Ω] 2. Burst-mode Frequency The burst-mode frequency is determined by a resistor RT and a capacitor connected to BCT pin. The frequency can be calculated by: 00 f [Hz] = Main Oscillator Frequency RT = 120kΩ 0 CT (pf) BCT[nF] RT[kΩ] Burst Mode Frequency RT = 56kΩ RT = 82kΩ C SST [uf] T[s] = I SST [ua] 6) Analog & Burst-mode Dimming The dimming control method is determined by the value of BPWM pin. The threshold of the BPWM is set at 0.5V. If the value of BPWM pin is less than 0.5V, the dimming control method is analog dimming. The analog dimming range is 0 ~ 2V. If the value of BPWM pin is more than 0.5V, the dimming control method is burstmode dimming. To compare the input of V DIM pin with the triangular wave(bct) makes the PWM pulses for Burst-mode Dimming. The BPWM pin is pulled to 4V to make the dark portion of the CCFL output burst and the floating state to make the bright portion. A less than 0.5V input on V DIM pin will obtain 0% brightness. 7) Frequency 1. Operation Frequency A resistor RT and a capacitor CT determine the main frequency of IC. The main frequency can be calculated as below equation: f BCT (Hz) 0 RT = 56kΩ RT = 120kΩ RT = 82kΩ 0 00 BCT (nf) 8) Protection 1. Open Lamp Protection Open lamp protection in the ignition time is provided through, SST and TIMER pin to ensure a rated voltage is achieved and a required timing is satisfied. If time that SST or TIMER capacitor charges to 2.5V is long than the CCFL ignition time, it can prevent over-operating by protection circuit. 2. When the output voltage reaches the threshold, it commands the PWM controller to maintain the current driving level. This ensures that output gets sufficient striking voltage while operating the power transformer safely. The threshold is set at 2V nominal. 5/7

6 TRANSIENT RESPONSE SST Timer u 200u 300u 400u 500u FULL-BRIDGE SIGNAL CONTROL POUT1 CMP CT PWMOUT A A' B B' NOUT1 POUT2 NOUT2 POUT1 Delay Overlap Delay 6/7

7 TRANSFORMER DESIGN Cs 1 L S1 2 T1 1 L S2 2 V IN -V IN 1 n C1 Cp LAMP FULL-BRIDGE POWER STAGE 1) Transformer Turns Ratio Calculation of the required turns ratio involves the estimation of two critical factors. 1. Estimating Minimum Primary Voltage. The minimum primary voltage is obtained from the value of the low supply voltage. 2. Estimating Maximum Secondary Voltage. The secondary is composed of the voltage divide capacitor and the lamp parasitic capacitor. The voltage across the secondary can be calculated as below equation: From the Faraday's law, the required number of secondary turns would be: V secondary 8 N secondary = where, B is the magnetic flux density. 3) Required Number of Primary Turns From the turns ratio and number of secondary turns N secondary N primary = N 4) Determination of Wire Gauge Wire gauge can be done by an acceptable current density. Vsecondary(rms) = 2 2 N VIN sin 2 D From the assumed current density (500cmil) and the current that flows through wires, the required Circular Mils is: Transformer turns ratio is: V secondary N = V primary 2) Required Number of Secondary Turns From the core constant provided by the core manufacturer, you will need the effective core cross sectional area(ae). Cmils = CD Lim I RMS From the AWG table, pick a wire-gauge that would fit limit. Using the selected wire diameter and bobbin information, determine if this wire gauge will fit in the space allotted. (when the space factor[sf] is accounted for) 7/7