The SM72485 step-down switching regulator features all of the functions required to implement a low cost, efficient, Buck bias regulator. This high voltage regulator contains an 100-V N-channel buck switch. The device is easy to implement and is provided in the VSSOP and the thermally enhanced WSON package. The regulator is based on a control scheme using an on-time inversely proportional to VIN. This feature allows the operating frequency to remain relatively constant. The control scheme requires no loop compensation. An intelligent current limit is implemented with forced off-time, which is inversely proportional to VOUT. This scheme ensures short circuit control while providing minimum foldback. Other features include: Thermal shutdown, VCC undervoltage lockout, gate drive undervoltage lockout, maximum duty cycle limiter, and a precharge switch.