Digitally programmable dual full-bridge MOSFET driver IC

5th April 2007

ES Admin

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The new A3985 from Allegro MicroSystems Europe is a digitally programmable dual full-bridge gate driver IC suitable for driving a wide range of higher power industrial bipolar two-phase stepper motors, two-phase brushless DC motors or dual brush DC motors in industrial, medical and office automation applications. The compact package of the A3985 means that a complete high-current microstepping motor driver or dual DC motor system can be implemented with limited PC board space. This is especially important in multi-axis systems where several drivers need to share one PC board.

Motor power is provided by external N-channel power MOSFETs at supply voltages from 12 V to 50 V. The A3985 provides all the necessary circuitry to ensure that the gate-source voltage of both high-side and low-side external MOSFETs is above 10 V and that the gate capacitance is quickly charged and discharged in order to reduce power dissipation during switching.

Full digital control is provided by two serially accessible registers that permit programming of off-time, blank-time, dead-time, mixed decay ratios, synchronous rectification, system oscillator source selection and division ratio and idle mode.

All internal timings are derived from a master clock that can be generated on-chip or provided by 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 or patented mixed current-decay modes. The desired load current level and direction are set via the serial port with a direction bit and two 6-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% increments of the maximum value.

The above-supply voltage required for the high-side N-channel external MOSFETs is provided by a bootstrap capacitor. Efficiency is enhanced by using synchronous rectification. The external MOSFETs are protected from shoot-through by integrated crossover control and programmable dead time.
Additional internal circuit protection includes thermal shutdown with hysteresis and undervoltage lockout. Special power-up sequencing is not required.

The A3985 is supplied in a lead (Pb) free 38-pin TSSOP package with 100% matt tin leadframe platting.