The A3955 is designed to drive 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 three-bit nonlinear digital-
to-analog converter allows the motor current to be controlled
in full-, half-, quarter-, or eighth-step (microstepping) modes.
Nonlinear increments minimize the number of control lines
necessary for microstepping. Microstepping provides 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 and 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.