Dual full-bridge MOSFET driver IC with microstepping translator

3rd October 2006
ES Admin
The A3986 from Allegro MicroSystems Europe is a dual full-bridge gate driver IC with integrated microstepping translator circuitry. The device is suitable for driving a wide range of industrial bipolar 2-phase stepper motors in the 30 to 500 W power range. Motor power is provided by external N-channel power MOSFETs at supply voltages from 12 to 50 V.
The A3986 contains two sinusoidal digital/analogue convertors that generate the reference voltage for two separate fixed off-time pulse-width-modulated current controllers. These provide current regulation for external power MOSFET full bridge circuits.

Motor stepping is controlled by the two-wire step and direction interface, providing complete microstepping control at full-, half-, quarter- and sixteenth-step resolutions. The fixed off-time regulator can operate in slow-, mixed- or fast-decay modes, which results in reduced audible motor
noise, increased step accuracy, and reduced power dissipation.

The translator is the key to the easy implementation of the driver IC. Simply inputting one pulse on the 'step' input drives the motor one step (full, half, quarter or sixteenth depending on the microstep select input). There are no phase-sequence tables, high-frequency control lines, or complex
interfaces to program, reducing the need for complex external microcontroller circuits.

The above-supply voltage required for the high-side N-channel MOSFETs is provided by a bootstrap capacitor. Efficiency is enhanced by using synchronous rectification, and the power FETs 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 undervoltage lockout. Special power-up sequencing is not required.

The A3986 is supplied in a 38-pin TSSOP surface-mount package. An optional lead- free version has 100% matt tin lead-frame plating.

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