7.1 Overview

The LM25011 constant on-time step-down switching regulator features all the functions needed to implement a low-cost, efficient buck bias power converter capable of supplying up to 2.0 A to the load. This high-voltage regulator contains an N-Channel buck switch, is easy to implement, and is available in a 10-pin VSSOP, PowerPAD power enhanced package. The operation of the regulator is based on a constant on-time control principle with the on-time inversely proportional to the input voltage. This feature results in the operating frequency remaining relatively constant with load and input voltage variations. The constant on-time feedback control principle requires no loop compensation resulting in very fast load transient response. The adjustable valley current limit detection results in a smooth transition from constant voltage to constant current when current limit is reached. To aid in controlling excessive switch current due to a possible saturating inductor, the on-time is reduced by approximately 40% when the current limit is detected. The Power Good output (PGD pin) indicates when the output voltage is within 5% of the expected regulation voltage.

The LM25011 can be implemented to efficiently step-down higher voltages in non-isolated applications. Additional features include: low output ripple, VIN under-voltage lock-out, adjustable soft-start timing, thermal shutdown, gate drive pre-charge, gate drive under-voltage lock-out, and maximum duty-cycle limit.