The LM5574 switching regulator features the functions necessary to implement an efficient high voltage buck regulator using a minimum of external components. This easy-to-use regulator integrates a 75V, N-Channel buck switch with an output current capability of 0.5 Amps. The regulator control method is based on current mode control using an emulated current ramp. Peak current mode control provides inherent line voltage feed-forward, cycle-by-cycle current limiting, and ease-of-loop compensation. The use of an emulated control ramp reduces noise sensitivity of the pulse width modulation circuit, which allows reliable processing of very small duty cycles necessary in high input voltage applications. The operating frequency is user programmable from 50kHz to 500kHz. An oscillator synchronization pin allows multiple LM5574 regulators to self-synchronize or be synchronized to an external clock. The output voltage can be set as low as 1.225V. Fault protection features include, current limiting, thermal shutdown, and remote shutdown capability. The device is available in the 16-pin TSSOP package.

The functional block diagram and typical application of the LM5574 are shown in Figure 6-1. The LM5574 can be applied in numerous applications to efficiently step-down a high, unregulated input voltage. The device is designed for telecom, industrial power bus voltage ranges.