3955
FULL-BRIDGE PWM
MICROSTEPPING MOTOR DRIVER
The A3955SB and A3955SLB 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 com-
bined 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.
LOAD
SUPPLY
16
PFD
REF
RC
1
2
3
V
BB
OUT
B
15
14
D
0
4
5
6
GROUND
GROUND
13 GROUND
LOGIC
Microstepping provides for increased step resolution, and reduces
torque variations and resonance problems at low speed.
12
11
GROUND
SENSE
LOGIC
SUPPLY
V
CC
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.
10 OUT
PHASE
7
8
A
9
D
2
D
1
Dwg. PP-056-2
Note the A3955SB (DIP) and the A3955SLB
(SOIC) are electrically identical and share a
common terminal number assignment.
Internal circuit protection includes thermal shutdown with hyster-
esis, transient-suppression diodes, and crossover current protection.
Special power-up sequencing is not required.
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage, VBB . . . . . . . . . . 50 V
Output Current, IOUT
(Continuous) . . . . . . . . . . . . . . ±1.5 A*
Logic Supply Voltage, VCC . . . . . . . . . 7.0 V
The A3955S— is supplied in a choice of two power packages; a
16-pin dual-in-line plastic package with copper heat-sink tabs (suffix
‘B’), and a 16-lead plastic SOIC with copper heat-sink tabs (suffix ‘LB’).
For both package styles, the power tab is at ground potential and
needs no electrical isolation.
Logic/Reference Input Voltage Range,
VIN . . . . . . . . . . . -0.3 V to VCC + 0.3 V
Sense Voltage, VS . . . . . . . . . . . . . . . . 1.0 V
Package Power Dissipation,
FEATURES
■ ±1.5 A Continuous Output Current
■ 50 V Output Voltage Rating
■ Internal PWM Current Control
■ 3-Bit Non-Linear DAC
■ Fast, Mixed Fast/Slow, and Slow Current-Decay Modes
■ Internal Transient-Suppression Diodes
■ Internal Thermal-Shutdown Circuitry
■ Crossover-Current and UVLO Protection
PD . . . . . . . . . . . . . . . . . . . . See Graph
Operating Temperature Range,
TA . . . . . . . . . . . . . . . . . -20˚C to +85˚C
Junction Temperature, TJ . . . . . . . +150˚C†
Storage Temperature Range,
TS . . . . . . . . . . . . . . . . -55˚C to +150˚C
* Output current rating may be limited by duty
cycle, ambient temperature, and heat sinking.
Under any set of conditions, do not exceed the
specified current rating or a junction temperature
of 150˚C.
† Fault conditions that produce excessive junction
temperature will activate the device’s thermal
shutdown circuitry. These conditions can be
tolerated but should be avoided.
Always order by complete part number:
Part Number
Package
A3955SB
16-Pin DIP
A3955SLB
16-Lead SOIC