A digital diode emulator (DDE) for a DC-DC converter increments a digital
counter with a high frequency clock. For each inductor current cycle, the
counter counts between turn-on and turn-off of the output switching
circuit's lower switch. When the contents of the counter match a
modification of a count latched from the previous inductor current cycle,
a turn-off signal is supplied to the control logic. If the previous
inductor current cycle's turn-off signal occurred late, the latched count
is decremented by one bit. If the previous cycle's turn-off signal occurs
early, the latched count is incremented by one bit. Over successive
inductor current cycles, the digital diode emulator effectively `dithers`
the turn-off time of the switching circuit's lower switch about the
zero-crossing point of the inductor current.
