Constant on time control circuit and DC-DC converting circuit

摘要

A constant on time control circuit, configured to control a converting circuit to transform an input voltage into a stable output voltage, is disclosed. The constant on time control circuit comprises a comparing circuit and a logic circuit. The comparing circuit compares a reference signal and a voltage signal indicative of the output voltage and accordingly outputs a compared result signal. The logic circuit periodically controls the converting circuit to perform voltage transformation and makes a time period of a duty cycle in every cycle being substantially constant. A start point in time of every cycle is determined according to the compared result signal. The comparing circuit comprises a differential pair, a base current source and an extra current source. The base current source provides a bias current to the differential pair. The extra current source provides a substantial ramp current to one channel in the differential pair.

主权项

1. A constant on time control circuit, adapted to control a converting circuit to transform an input voltage into an output voltage, comprising:
a comparing circuit, comparing a reference signal and a voltage signal indicative of the output voltage and accordingly outputting a compared result signal; and a logic circuit, periodically controlling the converting circuit to perform the voltage transformation and make a time period of a duty cycle in every cycle being substantially constant, wherein a start point in time of every cycle is determined according to the compared result signal; wherein, the comparing circuit has a differential pair, a base current source and an extra current source, the base current source provides a bias current for the differential pair which compares the reference signal and the voltage signal to output the compared result signal, and the extra current source provides a substantial ramp current to one channel in the differential pair wherein the extra current source comprises a capacitance, a charging current source, a discharging current source and a transconductance circuit, wherein a current of the discharging current source is determined according to the voltage of the capacitance.