Block Diagram

Operation

The LM2651 operates in a constant frequency (300 kHz),

current-mode PWM for moderate to heavy loads; and it auto-

matically switches to hysteretic mode for light loads. In hys-

teretic mode, the switching frequency is reduced to keep the

efficiency high.

Main Operation

When the load current is higher than the sleep mode thresh-

old, the part is always operating in PWM mode. At the begin-

ning of each switching cycle, the high-side switch is turned

on, the current from the high-side switch is sensed and com-

pared with the output of the error amplifier (COMP pin).

When the sensed current reaches the COMP pin voltage

level, the high-side switch is turned off; after 40 ns (dead-

Current Limit vs Junction

Temperature (V

DS100925-13

Current Limit vs Input

Voltage (V

DS100925-14

DS100925-3

FIGURE 1. LM2651 Block Diagram

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