Abstract: A power down brake latch circuit for dynamically braking a spindle motor in a disk drive system is disclosed. The power down brake latch circuit includes a reservoir capacitor, a smoothing capacitor, a timing circuit, and a logic circuit. The timing circuit includes a voltage divider and a bandgap comparator. The smoothing capacitor absorbs a BEMF voltage from the spindle motor as it rotates after losing power. The timing circuit generates a first signal when a voltage on the smoothing capacitor falls below a threshold. The logic circuit brakes the spindle motor in response to the loss of power and the generation of the first signal.

Abstract: A circuit for determining an initial winding combination for motor startup of a polyphase dc motor having a transistor driver circuit comprising a plurality of high side winding drivers and low side winding drivers operably connected to first and second voltage sources comprises a current mirror circuit and a plurality of sense FETs each operably connected between one of the voltage sources and the gate of one of the winding driver transistors in each phase combination. The sense FETs are operably connected to one side of the current mirror circuit. The mirror circuit compares the current through the sense FET with a current threshold provided on the other side of the current mirror and produces an output signal when the threshold is reached. At the same time, the time to reach the threshold is measured and the phase combination having the longest time is stored.