Abstract: A bootstrap reference circuit includes a shunt regulator for generating a reference voltage at a first node, a current source generating a current, and a current mirror coupling the current to the shunt regulator for supplying the shunt regulator. In operation, when the shunt regulator is powering up, the current has an increasing magnitude when a voltage at the first node is less than a predefined voltage value where the predefined voltage value is less than the reference voltage. Furthermore, the current has a decreasing magnitude when the voltage at the first node is greater than the predefined voltage value. In one embodiment, the shunt regulator includes a bandgap reference circuit and the predefined voltage value is less than the bandgap voltage of 1.24 volts.

Abstract: A bootstrap reference circuit includes a shunt regulator for generating a reference voltage at a first node, a current source generating a current, and a current mirror coupling the current to the shunt regulator for supplying the shunt regulator. In operation, when the shunt regulator is powering up, the current has an increasing magnitude when a voltage at the first node is less than a predefined voltage value where the predefined voltage value is less than the reference voltage. Furthermore, the current has a decreasing magnitude when the voltage at the first node is greater than the predefined voltage value. In one embodiment, the shunt regulator includes a bandgap reference circuit and the predefined voltage value is less than the bandgap voltage of 1.24 volts. The decreasing current improves the stability of the bootstrap reference circuit, preventing voltage overshoots that can occur as the shunt regulator reaches regulation.

Abstract: A method of parking the head by first moving the head toward the inner diameter of the disc an then back across the disc and parking the head on a flat part of a ramp. In one embodiment, a moderate voltage on the motor drives the head toward the inner diameter of the disc until the head hits the inner crash stop and then a moderate current drives the head back across the disc to give the head enough momentum to get to the flat part of he ramp. In another embodiment, more stages, each having a different voltage, are used to get better control of the velocity of the head as it is being driven across the disc. A higher voltage is also used to turn the head to move toward the inner diameter of the disc when it is moving fast toward the outer diameter. A retract circuit controls the movement of the head during retract. To be able to drive the head in the tow directions, the retract circuit needs to be bipolar, containing both a current source and a current sink. Counters are used to time the driving of the head.

Abstract: A circuit for controlling the slew rate at a motor coil during turn-on in a commutation sequence is disclosed. The disclosed circuit includes a switched current mirror that receives the commutation signal, and that provides a mirrored current to the input of an integrating buffer amplifier when its associated coil is to be driven. The integrating buffer amplifier includes an amplifier with a feedback capacitor, and a current source connected at its input, for reducing the voltage slew rate during turn-off of the transistor. The mirrored current applied to the input on the integrating buffer amplifier is greater than that of the current source, but limited so as to reduce the voltage slew at the coil.

Abstract: A circuit for controlling the slew rate at a motor coil during turn-on in a commutation sequence is disclosed. The disclosed circuit includes a switched current mirror that receives the commutation signal, and that provides a mirrored current to the input of an integrating buffer amplifier when its associated coil is to be driven. The integrating buffer amplifier includes an amplifier with a feedback capacitor, and a current source connected at its input, for reducing the voltage slew rate during turn-off of the transistor. The mirrored current applied to the input of the integrating buffer amplifier is greater than that of the current source, but limited so as to reduce the voltage slew at the coil.

Abstract: A method and circuit for braking a forward rotation of a rotor of a polyphase DC motor. A commutation sequencer is incremented by several phases to produce an incremented commutation sequence to produce a magnetic flux vector that lags a magnetic pole of the motor. Driving currents are applied to coils of the motor in accordance with the incremented commutation sequence to brake the rotor. The method is implemented in a circuit that has a sequencer for incrementally generating sets of commutation signals to select stator coils for energization to rotate the rotor. A power stage to which the commutation signals are applied energizes the selected coils in accordance with the commutation signals. A circuit interrupts the energization of the selected coils and the commutation sequence is altered to produce a sequence that produces a negative torque on the rotor.

Abstract: A method and apparatus for switching a motor between bipolar and unipolar mode. During each phase of the bipolar mode, one of the coils floats and has a back emf. In the method, first, a mode change signal requesting a change between the bipolar mode and the unipolar mode is received. Second, the back emf across the floating coil is monitored. Third, a point in time when the back emf equals the center tap voltage is detected. Last, the motor is switched between the bipolar mode and the unipolar mode at a point away from point in time when the back emf across the floating coil equals the center tap voltage. Various circuitry is also disclosed for switching a motor between a bipolar mode and a unipolar mode.

Abstract: A circuit for clamping the voltage spike of a stator coil winding of a brushless direct current motor is disclosed. The circuit uses a comparator to monitor the voltage on a stator winding. When a voltage spike is detected, the comparator turns on the stator winding driver transistor to clamp the voltage spike. The comparator can be designed to trigger at a desired threshold voltage so that the threshold can optimized. Additionally, the comparator can be selectively disabled to trigger when voltage spikes are anticipated.

Abstract: A method and circuit for providing a dual slew rate to a driver transistor. The method includes turning off a driver transistor at a programmable slew rate until a BEMF voltage spike is sensed, and then switching in a slower clamping slew rate. The slew rates are controlled by discharging a capacitor through a programmable discharge path until a voltage spike is detected and then through a clamping discharge path. The discharge paths include several transistors connected in series and control by digital logic.

Abstract: Circuitry for selectably connecting the body node of drive transistors of a motor control circuit. In particular, those transistors that are turned off when operating the motor in a unipolar mode have their body nodes switched so as to be connected to a reference voltage, such as ground, during unipolar mode, and to be connected to the transistor source during bipolar mode (i.e., when the transistors are active). The circuitry also is operable to briefly connect the body nodes of the transistors to their source when the opposing drive transistor is commutated, in the unipolar mode. In this way, forward biasing of inherent diodes in the drive transistor is avoided in unipolar mode, except when useful to clamp the inductive kick of the motor coils.

Abstract: A chopper stabilized current amplifier circuit is disclosed. The current amplifier circuit includes a main operational transconductance amplifier, a nulling transconductance amplifier, two capacitors, four switches, and a timing control circuit. The timing control circuit uses analog inverters to decrease the slew rate of the switching of the switches to decrease the noise in the system.

Abstract: A method and circuit for braking a forward rotation of a rotor of a polyphase DC motor. A commutation sequencer is incremented by several phases to produce an incremented commutation sequence to produce a magnetic flux vector that lags a magnetic pole of the motor. Driving currents are applied to coils of the motor in accordance with the incremented commutation sequence to brake the rotor. The method is implemented in a circuit that has a sequencer for incrementally generating sets of commutation signals to select stator coils for energization to rotate the rotor. A power stage to which the commutation signals are applied energizes the selected coils in accordance with the commutation signals. A circuit interrupts the energization of the selected coils and the commutation sequence is altered to produce a sequence that produces a negative torque on the rotor.