Method and apparatus for speed control of voice coil motor retract operation dependent upon available power

摘要

The back EMF (BEMF) of a motor is sensed and compared to a target back EMF (BEMF) to generate an error control signal. The circuit supply voltage is also sensed. A PWM motor control signal is generated in response to a comparison of the error control signal to a ramp signal having a variable slope. The variable slope is selected in response to the sensed circuit supply voltage. The motor is then driven in response to the PWM control signal. The sign of the error control signal is used to selectively short one of motor terminals to a reference voltage supply node while the other motor terminal is driven in response to the PWM control signal.

主权项

1. A circuit for driving a motor having a positive terminal and negative terminal, comprising:
a drive circuit configured to be coupled to the positive and negative terminals of the motor and operable to drive motor operation; a back EMF (BEMF ) sensing circuit configured to be coupled to the positive and negative terminals of the motor and operable to sense motor BEMF; an error circuit operable to compare the sensed motor BEMF to a target BEMF and generate a motor control signal in response to said comparison; a power supply sensing circuit configured to sense a supply voltage of the drive circuit; and a pulse width modulation (PWM) circuit configured to generate a PWM control signal in response to a comparison of the motor control signal to a ramp signal having a variable slope, wherein the variable slope is selected in response to the sensed supply voltage; wherein operation of said drive circuit is controlled in response to said PWM control signal.