KA7540

www.fairchildsemi.com KA7540 Simple Dimming Ballast Control IC Features Internal soft start No lamp protection Voltage controlled dimming Trimmed 1.5% internal bandgap reference Under voltage lock out with 1.8V of hysteresis Totem pole output with high state clamp Low start-up and operating current 8-pin DIP & 8-pin SOP Descriptions The KA7540 provides simple and high performance electronic ballast control functions. KA7540 is optimized for electronic ballast requiring a minimum board area, reduced component count and low power dissipation. Internal soft start circuitry eliminates the need for an external soft start PTC resistor. Voltage controlled dimming circuit is built into the IC to control the lighting output in a wide range. Protection circuitry has also been added to prevent switches from burning out in no lamp condition. Output gate drive circuit clamps power MOSFET gate voltage irrespective of supply voltage. 8-DIP Applications Electronic Ballast Lighting Control System Half-bridge Drive Control System 1 8-SOP 1 Rev. 1.0.1 ©2001 Fairchild Semiconductor Corporation KA7540 Internal Block Diagram UVLO 2V Ref CS 6.8µF 1 25µA VZ Vref − + 17µA VZ IS UVLO Internal bias 1.8V + − 12.5V 8 VCC Oscillator Ct 180pF 8Ict 2 Ict latch + Q + + IC 7 OUT 1 F.D from VCS Vdim 3 80kΩ Vd 20kΩ 100µA 3pF VCC Id + − kVref VZ Frequency divider 6 OUT 2 Ldet 40kΩ 4 5pF 2V 25µA − + Shut down signal IS = 17µA × (Vref − VSS) / Vref Id = 25µA × (Vref − ...