A3957SLBTR

**The A3957SA and A3957SLB are designed for driving one winding of a

bipolar stepper motor in a microstepping mode. The outputs are rated for continuous output currents to ±1.5 A and operating voltages to 50 V. Internal pulse-width modulated (PWM) current control combined with an internal four-bit nonlinear digital-to-analog converter allows the motor current to be controlled in full-, half-, quarter-, eighth-, or sixteenth-step (microstepping) modes. Nonlinear increments minimize the number of control lines necessary for microstepping. Microstepping provides for increased step resolution, and reduces torque variations and resonance problems at low speed.**

Internal circuitry determines whether the PWM current-control circuitry operates in a slow (recirculating) current-decay mode, fast (regenerative) current-decay mode, or in a mixed current-decay mode in which the off time is divided into a period of fast current decay with the remainder of the fixed off time spent in slow current decay. The combination of user-selectable current-sensing resistor and reference voltage, digitally selected output current ratio; and slow, fast, or mixed current-decay modes provides users with a broad, variable range of motor control.
Internal circuit protection includes thermal shutdown with hysteresis, transient-suppression diodes, and crossover current protection. Special power- up sequencing is not required.
The A3957S— is supplied in a choice of two power packages; a 16-pin dual-in- line plastic package (suffix ‘A’), and a 24-lead plastic SOIC with copper heat-sink tabs (suffix ‘LB’). The power tab is at ground potential and needs no electrical isolation.

FEATURES

■ ±1.5 A Continuous Output Current
■ 50 V Output Voltage Rating
■ Internal PWM Current Control
■ 4-Bit Non-Linear DAC for 16-Bit Microstepping
■ Satlington™ Sink Drivers
■ Fast, Mixed Fast/Slow, and Slow Current-Decay Modes
■ Internal Transient-Suppression Diodes
■ Internal Thermal-Shutdown Circuitry
■ Crossover-Current and UVLO Protection