A constant-on-time power-supply controller includes an adder and a control
circuit. The adder generates a sum of a sense voltage and a regulated
output voltage generated by a filter inductor. The sense voltage is
generated by a sense circuit that sources a current to the filter
inductor while the inductor is uncoupled from an input voltage, and the
sense voltage is related to the current. The control circuit couples the
filter inductor to the input voltage for a predetermined time in response
to the sum having a predetermined relationship to a reference voltage.
Such a power-supply controller may yield a relatively tight regulation of
the output voltage even with a power supply having with a low-ESR filter
capacitor, and may do so with little or no additional compensation
circuitry as compared to prior controllers and with no additional pin on
the power-supply-controller chip.