The LM5009 step-down switching regulator features all of the functions needed to implement a low-cost, efficient, buck bias regulator. This device is capable of driving a 150-mA load current from a 9.5-V to 95-V input source. The switching frequency can exceed 600 kHz, depending on the input and output voltages. The output voltage can be set from 2.5 V to 85 V. This high-voltage regulator contains an N-channel buck switch and an internal startup regulator. The device is easy to implement and is provided in 8-pin VSSOP and thermally-enhanced, 8-pin WSON packages. The LM5009 is a well-suited alternative to a high-voltage monolithic or discrete linear solution where the power loss becomes unacceptable. The regulator operation is based on a control scheme using an on-time inversely proportional to VIN. This feature allows the operating frequency to remain relatively constant over load and input voltage variations. The control scheme requires no loop compensation, resulting in an ultrafast transient response. An intelligent current limit is implemented with forced off-time that is inversely proportional to V_OUT. This scheme ensures short-circuit protection and provides minimum foldback. Other features include thermal shutdown, V_CCundervoltage lockout, gate drive undervoltage lockout, and maximum duty cycle limiter.