A3955
Full-Bridge PWM Microstepping Motor Driver
Features and Benefits
Description
▪ ±1.5 A continuous output current
▪ 50 V output voltage rating
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
voltagesto50V.Internalpulsewidthmodulated(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
necessaryformicrostepping.Microsteppingprovidesincreased
step resolution, and reduces torque variations and resonance
problems at low speed.
▪ Internal PWM current control
▪ 3-bit nonlinear DAC
▪ Fast, mixed fast/slow, and slow current-decay modes
▪ Internal transient-suppression diodes
▪ Internal thermal shutdown circuitry
▪ Crossover-current and UVLO protection
InternalcircuitrydetermineswhetherthePWMcurrent-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.
Packages:
Package B, 16-pin DIP
with exposed tabs
Package LB, 16-pin SOIC
with internally fused pins
Not to scale
Continued on the next page…
Functional Block Diagram
10
15
6
16
PHASE
V
CC
7
V
BB
GROUND
4
5
UVLO
& TSD
12
13
BLANKING
GATE
CURRENT-SENSE
COMPARATOR
SENSE
MIXED-DECAY
COMPARATOR
PWM LATCH
R
Q
S
11
+
–
PFD
1
+
–
÷3
D/A
BLANKING
DISABLE
R
S
V
CC
+ –
RC
3
V
TH
2
8
9
14
C
T
R
T
Dwg. FP-042
29319.41E