A projected on-time (POT) switching regulator is provided. The regulator
includes a switching regulator controller and a main switch. The
controller includes a feedback comparator and an on-timer. The feedback
comparator compares the output voltage to a reference voltage. Whenever
the feedback comparator trips, the main switch is turned on, and the
on-timer controls the turn-on duration (on-time) of the main switch,
where the duration is adjusted by the input and output voltages according
to a preset transfer function. The transfer function is applicable to
both CCM and DCM operation. However, during CCM mode operation, at least
above a minimum on-time, the on-time is adjusted so that the switching
frequency of the regulator is approximately constant. The on-timer
includes a comparator that compares an adjustable voltage VFQ to a ramp
voltage VIFQ generated by providing an adjustable current IFQ to a
capacitor CREF. VFQ and IFQ are adjusted so that, during CCM mode
operation, at least above the minimum on-time, the switching frequency of
the regulator is approximately constant.