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Dual full-bridge gate driver eases motor control

Posted: 22 Nov 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Allegro? A3985? gate driver? industrial motors? MOSFETs?

Allegro MicroSystems' A3985 is a digitally programmable dual full-bridge gate driver for industrial bipolar two-phase stepper motors, two-phase brushless DC motors or two individual torque motors.

For the industrial, medical and office automation markets, the chip is suited for use in a synchronous rectification system with external n-channel power MOSFETs (12-50V source). Off-time, blank-time, dead-time, mixed decay ratios, system oscillator source selection and division ratio and idle mode are programmed via two serial registers. All internal timing is derived from an on-chip master clock (or alternatively, from an external system clock). A programmable divider allows for a wide range of external system clock frequencies.

The internal fixed off-time PWM current-control timing is programmed via the serial interface to operate in slow, fast and mixed current-decay modes. The desired load current level and direction is set via the serial port with a direction bit and two six-bit linear DACs in conjunction with a reference voltage. The seven bits of control allow maximum flexibility in torque control for a variety of step methods, from microstepping to full-step drive. Load current in the external power MOSFET full-bridges is set in 1.56 percent increments of the maximum value.

The chip is protected from shoot through (integrated crossover control and programmable dead time). The chip includes thermal shutdown circuitry with hysteresis and undervoltage lockout. Special power-up sequencing is not required.

The A3985, in a Pb-free 38-pin TSSOP package with 100 percent matte tin leadframe platting, is priced at $3.87 each in 1,000 quantities. Typical lead time is 12 weeks.

- Vince Biancomano

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