CS3842B

CS3842B/3843B CS3842B/CS3843B Off-Line Current Mode PWM Control Circuit with Very Low Start Up Current Description The CS384XB provides all the necessary features to implement off-line fixed frequency current-mode control with a minimum number of external components. The family has been optimized for very low start up current (300µA, typ). The CS384XB family incorporates a precision temperature-controlled oscillator with an internally trimmed discharge current to minimize variations in frequency. A precision duty-cycle clamp eliminates the need for an external oscillator when a 50% duty-cycle is used. Duty-cycles of almost 100% are possible. On board logic ensures that VREF is stabilized before the output stage is enabled. Ion-implant resistors provide tighter control of undervoltage lockout. Other features include pulse-by-pulse current limiting, and a high-current totem pole output for driving capacitive loads, such as the gate of a power MOSFET. The output is LOW in the off state, consistent with N-channel devices. These ICs are available in 8 and 14 lead surface mount (SO) and 8 lead PDIP packages. Features s Very low Start Up Current (300µA typ) s Optimized Off-line Control s Internally Trimmed, Temperature Compensated Oscillator s Maximum Duty-cycle Clamp s VREF stabilization before Output Enable s Pulse-by-pulse Current Limiting s Improved Undervoltage Lockout s Double Pulse Suppression s 1% Trimmed Bandgap Reference s High Current Totem Pole Output Absolute Maximum Ratings Supply Voltage (ICC