Features
- Serial interface for full digital control
- Dual full-bridge gate drive for N-channel MOSFETs
- Dual 6-bit DAC current reference
- Operation over 12 to 50 V supply voltage range
- Synchronous rectification
- Cross-conduction protection
- Adjustable mixed decay
- Fixed off-time PWM current control
- Low-current idle mode
Description
The A3985 is a flexible dual full-bridge gate driver suitable for driving a wide range of higher power industrial bipolar 2-phase stepper motors or 2-phase brushless dc motors. It can also be used to drive two individual torque motors or solenoid actuators. Motor power is provided by external N-channel power MOSFETs at supply voltages from 12 to 50 V.
Full digital control is provided by two serially-accessible registers that allow programming of off-time, blank-time, dead-time, mixed decay ratios, synchronous rectification, master clock 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 clock such as the system clock of the master controller. 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 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 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. This component is supplied in a 38-pin TSSOP (package LD) with 100% matte tin leadframe plating.
Functional Block Diagram
