Motor control circuit with adaptive dynamic range selection

The claimed invention relates generally to the field of motor driver circuits and more particularly, but not by way of limitation, to an apparatus and method for operating a disc drive spindle motor which supports a rotatable magnetic recording disc. Method and apparatus for controlling a motor. A digital to analog converter (DAC) converts input digital values to corresponding analog voltages over a range of different selectable dynamic operating ranges. A first motor adjustment signal within a first dynamic range of the DAC is generated in relation to a velocity error of the motor, and applied to the DAC to control flow of current through the motor. The DAC is adjusted to a different, second dynamic range when the first motor adjustment signal is proximate an upper end or a lower end of the first dynamic range. Expanding the dynamic range allows greater amounts of current to be applied to the motor; contracting the dynamic range provides higher resolution (volts/count) and greater stability. The different ranges are automatically selected for different motor load conditions.