This paper describes a digital pulse-width modulation/pulse-frequency modulation (PWM/PFM) controller with input voltage feed-forward for synchronous buck DC-DC converters. The controller includes automatic PWM/PFM mode switching and effective synchronous operation with a minimum number of active components and without the need for current sensing in PFM mode of operation. Input-voltage feed-forward improves efficiency and dynamic performance over a wide range of input voltages. Controller parameters, including the PWM switching frequency, the PFM pulse period, and the mode transition point are programmable, which enables efficiency optimization. Experimental results are shown for a synchronous buck converter with 5-to-12 V input voltage, and 1.3 V, 0 - 10 A output.
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