Patent attributes
A circuit and method for gradually reducing a coil current during a shutdown period is disclosed. The circuit and method include a controller that is configured in a control loop with a current sensor that measures the current in the coil and a transistor that can be controller to limit the current in the coil. The open-loop gain of the controller is determined by a resistance of a variable feedback resistor, and the resistance of the variable feedback resistor is reduced during the shutdown period as the coil current becomes small. The reduction of the resistance maintains a suitable phase margin by lowering the open loop gain of the circuit for low coil currents. Thus during shutdown, the circuit provides control accuracy for high coil currents and control stability for low coil currents.
