Low power switching mode regulator having automatic PFM and PWM operation

摘要

A circuit and method for operating a switching mode power supply. A clock is driven by a current source to generate pulses at a fixed frequency using pulse width modulation for normal load demands. For light load demands, the current to the clock is reduced, and therefore the clock generates pulses at a lower, variable frequency and fixed duration using pulse frequency modulation. Thus, depending on the load condition, either fixed frequency pulses or fixed duration pulses are automatically provided to a power stage for conversion to an output voltage.

主权项

1. A switching mode power supply circuit, comprising:
a pulse generation circuit including an oscillator that is always on, the oscillator being configured to generate pulses using pulse width modulation for a first load condition that exceeds a predefined threshold and configured to generate pulses using pulse frequency modulation for a second load condition that does not exceed the predefined threshold; a power stage coupled to the pulse generation circuit and configured to convert an input voltage to a modulated voltage at a switching node using pulses generated by the pulse generation circuit; a clock circuit coupled to the power stage and to a bias current source, the bias current source driving the clock to generate pulses to drive the power stage; a circuit to take away some of current generated by the bias current source to operate the switch mode power supply in a pulse frequency modulation (PFM) mode; and an output filter circuit coupled to the switching node and configured to produce an output voltage from the modulated voltage.