Dual Full-Bridge MOSFET Driver is digitally programmable.

Press Release Summary:

Model A3985 powers bipolar 2-phase stepper motors and 2-phase brush/brushless dc motors through external N-channel power MOSFETs at supply voltages ranging from 12-50 V. Driver ensures gate-source voltage of high-side and low-side external MOSFETs are above 10 V. Two serially accessible registers provide digital control, while internal circuit protection provides thermal shutdown with hysteresis and under-voltage lockout.

Original Press Release:

Allegro Announces New Digitally Programmable Dual Full-Bridge MOSFET Driver

Efficient Bipolar Solution with Minimal External Components

Worcester, MA, November 15, 2006 - Allegro MicroSystems, Inc. announces the release of a new digitally programmable dual full-bridge gate driver suitable for driving a wide range of higher power industrial bipolar two-phase stepper motors, two-phase brushless DC motors or two brush DC motors. Allegro's A3985 is targeted at the industrial, medical and office automation markets.

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 are above 10 V, and 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, and patented 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% increments of the maximum value.

Using synchronous rectification enhances efficiency and the external power MOSFETs are protected from shoot through by integrated crossover control and programmable dead time. In addition to crossover current control, internal circuit protection provides thermal shutdown with hysteresis and under-voltage lockout. Special power up sequencing is not required.

Allegro's A3985 is supplied in a (Pb) free 38-pin TSSOP package with 100% matte tin leadframe platting. The A3985SLD-T is priced at $3.87 in quantities of 1,000 and has a 12 week typical lead-time to market. For this information on this part please access the datasheet at www.allegromicro.com/sf/3985.

About Allegro
Allegro MicroSystems, Inc. is a supplier of advanced mixed-signal power semiconductors and Hall-effect sensors targeted toward the automotive, communications, computer/office automation, consumer and industrial markets. Allegro maintains a leadership position in the integrated magnetic sensor and integrated motor driver product segments. With more than 2,000 employees, Allegro is headquartered in Worcester, MA. Further information about Allegro, including free samples of our products, can be found at www.allegromicro.com.

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