A constant on-time pulse width control-based apparatus used in a voltage converter includes a comparator, a logic circuit, and a controller. The comparator is configured for generating a logic control signal to a logic circuit according to two resultant signals of the controller. The logic circuit is configured for generating a pulse control signal with an on-time pulse width to charge an output capacitor of an output stage circuit of the voltage converter according to the logic control signal. The controller is configured for generating the two resultant signals to the comparator by detecting an inductor current signal from an inductor of the output stage circuit, generating a voltage ramp signal, amplifying and generating an output voltage ripple signal based on a reference voltage.