CONTROLLER CIRCUIT OF STEP-DOWN DC/DC CONVERTER AND IN-VEHICLE POWER SUPPLY SYSTEM

Provided is a controller circuit of a step-down DC/DC converter, the controller circuit including a ramp voltage generating circuit that generates a periodic ramp voltage, a clamp voltage generating circuit that generates a clamp voltage, an error amplifier that generates an error signal that depends on an error between an electrical state of the step-down DC/DC converter and a target state of the electrical state, a clamp circuit that clamps the error signal by using the clamp voltage, and a pulse width modulation comparator that compares the error signal resulting from the clamping by the clamp circuit with the ramp voltage. The ramp voltage generating circuit includes a first capacitor, a first current source, a switch, a second capacitor, and a driver circuit. The clamp voltage generating circuit includes a third capacitor, a fourth capacitor, a first resistor, and a second current source.