A method for detecting zero-current of a voltage converter includes resetting a comparator output during a first period when a power switch of the voltage converter is turned on, and receiving, by an offset cancellation circuit, sample signals from the comparator. The method also determines a comparator offset using the sample signals. In response to an output voltage of the voltage converter being less than a threshold voltage, the comparator output is reset during a second period when the power switch is turned off. The comparator compares a first signal from the voltage converter with a second signal representing a ground voltage to generate a ZCD signal indicative of a comparison of the first and second signals. Then, an offset cancellation signal indicative of the determined comparator offset is generated to cancel the comparator offset.