A constant on-time device is essentially the same as a hysteretic except there is an added block referred to as an on-timer. The key to this is that the on-time is set inversely proportional to the input voltage. This can be done quite simply with a resistor that is pulled up to the input voltage. The function is similar to the hysteretic control shown on the previous slide. In this case the comparator is only used for one threshold, the falling threshold. When the output voltage falls to the lower threshold, it triggers the non-resettable on-time which turns on the high side switch. The output voltage will rise during the on-time. When the timer expires, it will turn off the switch and the voltage will fall again. The COT control circuit will maintain regulation in that way.