A reference compensating circuit used in a COT control circuit. The reference compensating circuit has an error amplifier, a first current sink, a resistor, a second current sink, a current source and a capacitor. The error amplifier amplifies the difference between a reference signal and a feedback signal and generates an error signal. Based on the error signal, the first current sink generates a current flowing out from a node of the reference compensating circuit. The resistor receives the reference signal at one terminal. The other terminal of the resistor is coupled to the node. The second current sink sinks a current from the node intermittently. The current source sources a current into the node. The capacitor is coupled between the node and a ground to provide a calibrated compensation reference signal to the COT control circuit.