A spread-spectrum power converter uses an inter-cycle duty-cycle error
compensation to achieve a combination of high-precision tracking of a
target average duty cycle and a favorable noise signature. The pulse
train consists of a series of cycles having cycle durations of a positive
integer of clock cycles, pulse durations of a whole number of clock
cycles, and duty cycles corresponding to a ratio of pulse durations over
cycle durations. The pulse durations are selected at least in part as
functions of a target average duty cycle, the respective cycle durations,
and a ripple (or other) error from other cycles in the train. The cycle
durations can also be in part a function of the target average duty cycle
so that the duty cycle errors can be minimized.