Stmicroelectronics Gmbh

Sgs-thomson Microelectronics Limited

Massimiliano Brambilla

Gianluca Colli

Karl M Schlager

Eugene C Lee

Chinh Dac Nguyen

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.

Power down brake latch circuit for a brushless DC motor

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.

Control of slew rate during turn-on of motor driver transistors

A driver circuit with an amplifier operated in a switching mode has threshold detectors with devices to compare the amplifier input and output voltage respectively to predetermined minimum and maximum levels representing fully off and fully on conditions for the driver circuit. The circuit provides signals to enable the amplifier to draw current from a supply only during transitions between the threshold levels and to otherwise disable the amplifier. The circuit is beneficial particularly when operating the amplifier from a voltage supply of very limited current capability, such as a charge pump voltage in an integrated circuit. The switching mode amplifier can be applied in high performance driver integrated circuits alone or in combination with innovative techniques for slew rate control and for preslewing the amplifier output that also provide high performance in compact circuit configurations.

Driver circuit including amplifier operated in a switching mode

A voltage ramp generator for a driver circuit is provided to give an output that is highly linear between zero and a maximum voltage has a combination of current sources or generators for charging and discharging a capacitor, with discharging performed by sequencing two different types of current sources. A first current source on the discharge side of the capacitor has transistors in cascode connected current mirrors and takes the capacitor voltage to a low value but not as low as zero. A second current source of a basic or simple current mirror then takes the capacitor voltage substantially to zero. The voltage ramp generator meets the requirements of high performance, integrated, driver circuits, particularly for achieving complete turn-off of a power device such as a DMOS transistor in a high side cascoded transistors goes up to a threshold near the full supply driver. It is optional to have two current sources for charging, also, where a first source with voltage and than a second source, in a basic current mirror, continues charging substantially to the supply voltage.

Driver circuit including slew rate control system with improved voltage

A preslewing circuit to rapidly drop a voltage on the gate of a power device in a power stage has a combination of a bipolar transistor and CMOS transistors. The gate voltage is brought down by the preslewing circuit to a level at which an output voltage can begin to change. The combination has high conduction and can be integrated readily, with good internal isolation, in a small chip area, thus having qualities desirable for high performance, integrated, driver circuits.

Driver circuit including preslewing circuit for improved slew rate

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.

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 comparator for comparing the output of error amplifier to the input of the input buffer amplifier. The comparator connects the output of the error amplifier to the input of the buffer amplifier only after the input has been charged at a controlled rate. 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-on of the transistor.

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San Jose, CA, United States of America

Massimiliano Brambilla