A3955
Full-Bridge PWM Microstepping Motor Driver
Discontinued Product
This device is no longer in production. The device should not be
purchased for new design applications. Samples are no longer available.
Date of status change: January 30, 2012
Recommended Substitutions:
For existing customer transition, and for new customers or new appli-
cations, refer to the
A4975.
NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan
for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The
information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no respon-
sibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
A3955
Full-Bridge PWM Microstepping Motor Driver
Features and Benefits
▪
±1.5 A continuous output current
▪
50 V output voltage rating
▪
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
Description
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.
Continued on the next page…
Packages:
Package B, 16-pin DIP
with exposed tabs
Not to scale
Package LB, 16-pin SOIC
with internally fused pins
Functional Block Diagram
LOGIC
SUPPLY
LOAD
SUPPLY
OUTA
OUTB
PHASE
7
6
V
CC
10
15
16
V
BB
GROUND
4
5
12
13
UVLO
& TSD
MIXED-DECAY
COMPARATOR
PWM LATCH
BLANKING
GATE
CURRENT-SENSE
COMPARATOR
SENSE
11
PFD
1
+
–
BLANKING
R
Q
S
+ –
RC
3
V TH
2
REF
+
–
÷3
D/A
DISABLE
V
CC
RS
8
D
2
9
D
1
14
D
0
RT
CT
Dwg. FP-042
29319.41G
A3955
Description (continued)
Full-Bridge PWM Microstepping Motor Driver
Internal circuit protection includes thermal shutdown with hysteresis,
transient-suppression diodes, and crossover-current protection.
Special power-up sequencing is not required.
The A3955 is supplied in a choice of two power packages; a 16-pin
dual-in-line plastic package with copper heat-sink tabs (suffix ‘B’),
Selection Guide
Part Number
A3955SB-T
A3955SLBTR-T
and a 16-lead plastic SOIC with internally fused pins (suffix ‘LB’).
For both package styles, the thermally enhanced pins are at ground
potential and need no electrical isolation. Both packages are lead
(Pb) free, with leadframe plating 100% matte tin.
Packing
16-pin DIP with exposed thermal tabs
16-pin SOICW with internally fused pins
Package
25 per tube
1000 per reel
Absolute Maximum Ratings
Characteristic
Load Supply Voltage
Logic Supply Voltage
Logic/Reference Input Voltage Range
Sense Voltage
Output Current, Continuous
Package Power Dissipation
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
Symbol
V
BB
V
CC
V
IN
V
S
I
OUT
P
D
T
A
T
J
(max)
T
stg
Range S
Fault conditions that produce excessive junction temperature
will activate the device’s thermal shutdown circuitry. These
conditions can be tolerated but should be avoided.
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 tempera-
ture of 150°C.
Notes
Rating
50
7.0
–0.3 to V
CC
+ 0.3
1.0
±1.5
See graph
–20 to 85
150
–55 to 150
Units
V
V
V
V
A
W
ºC
ºC
ºC
Thermal Characteristics
Characteristic
Package Thermal Resistance, Junction
to Ambient
Package Thermal Resistance, Junction
to Tab
Symbol
R
θJA
Test Conditions*
2
B Package, single-layer PCB, 1 in. 2-oz. exposed copper
2
LB Package, 2-layer PCB, 0.3 in. 2-oz. exposed copper each
side
Value
43
67
6
Units
ºC/W
ºC/W
ºC/W
R
θJT
*Additional thermal information available on Allegro website.
ALLOWABLE PACKAGE POWER DISSIPATION (W)
4
R
θJT
= 6.0°C/W
3
SUFFIX 'B', R
θJA
= 43°C/W
2
1
SUFFIX 'LB', R
θJA
= 67°C/W
0
25
50
75
100
TEMPERATURE IN °C
125
150
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A3955
Full-Bridge PWM Microstepping Motor Driver
ELECTRICAL CHARACTERISTICS at T
A
= 25°C, V
BB
= 5 V to 50 V, V
CC
= 4.5 V to 5.5 V
(unless otherwise noted.)
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Power Outputs
Load Supply Voltage Range
Output Leakage Current
V
BB
I
CEX
V
CE(SAT)
Operating, I
OUT
= ±1.5 A, L = 3 mH
V
OUT
= V
BB
V
OUT
= 0 V
Output Saturation Voltage
(Forward or Reverse Mode)
V
S
= 1.0 V:
Source Driver, I
OUT
= -0.85 A
Source Driver, I
OUT
= -1.5 A
Sink Driver, I
OUT
= 0.85 A
Sink Driver, I
OUT
= 1.5 A
Sense Current Offset
Clamp Diode Forward Voltage
(Sink or Source)
Motor Supply Current
(No Load)
I
SO
V
F
I
BB(ON)
I
BB(OFF)
D
0
= D
1
= D
2
= 0.8 V
I
S
- I
OUT
, I
OUT
= 850 mA,
V
S
= 0 V, V
CC
= 5 V
I
F
= 0.85 A
I
F
= 1.5 A
—
—
—
—
20
—
—
—
—
1.0
1.3
0.5
1.3
33
1.2
1.4
2.0
1.0
1.2
1.5
0.6
1.5
40
1.4
1.7
4.0
50
V
V
V
V
mA
V
V
mA
μA
V
CC
—
—
—
<1.0
<-1.0
50
50
-50
V
μA
μA
Continued next page…
Table 1 — PHASE Truth Table
PHASE
H
L
OUT
A
H
L
OUT
B
L
H
Table 3 — DAC Truth Table
DAC DATA
D
2
D
1
D
0
H
H
H
H
L
L
L
L
H
H
L
L
H
H
L
L
H
L
H
L
H
L
H
L
Current
Ratio, %
100
92.4
83.1
70.7
55.5
38.2
19.5
V
REF
/V
S
3.00
3.25
3.61
4.24
5.41
7.85
15.38
Table 2 — PFD Truth Table
V
PFD
≥3.5
V
1.1 V to 3.1 V
≤0.8
V
Description
Slow Current-Decay Mode
Mixed Current-Decay Mode
Fast Current-Decay Mode
All Outputs Disabled
where V
S
= I
TRIP
•R
S
. See Applications section.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A3955
Full-Bridge PWM Microstepping Motor Driver
ELECTRICAL CHARACTERISTICS (continued) at T
A
= 25°C, V
BB
= 5 V to 50 V, V
CC
= 4.5 V to
5.5 V (unless otherwise noted. )
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Control Circuitry
Logic Supply Voltage Range
Reference Voltage Range
UVLO Enable Threshold
UVLO Hysteresis
Logic Supply Current
Logic Input Voltage
Logic Input Current
Mixed-Decay Comparator
Trip Points
I
CC(ON)
I
CC(OFF)
V
IN(1)
V
IN(0)
I
IN(1)
I
IN(0)
V
PFD
V
IN
= 2.0 V
V
IN
= 0.8 V
Slow Current-Decay Mode
Mixed Current-Decay Mode
Fast Current-Decay Mode
Mixed-Decay Comparator
Input Offset Voltage
Mixed-Decay Comparator
Hysteresis
Reference Input Current
Reference Divider Ratio
Digital-to-Analog Converter
Accuracy*
Current-Sense Comparator
Input Offset Voltage*
Step Reference
Current Ratio
V
IO(PFD)
∆V
IO(PFD)
I
REF
V
REF
/V
S
—
V
IO(S)
SRCR
V
REF
= 0 V to 2.5 V
at trip, D
0
= D
1
= D
2
= 2 V
1.0 V < V
REF
2.5 V
0.5 V < V
REF
1.0 V
V
REF
= 0 V
D
0
= D
1
= D
2
= 0.8 V
D
0
= 2 V, D
1
= D
2
= 0.8 V
D
0
= 0.8 V, D
1
= 2 V, D
2
= 0.8 V
D
0
= D
1
= 2 V, D
2
= 0.8 V
D
0
= D
1
= 0.8 V, D
2
= 2 V
D
0
= 2 V, D
1
= 0.8 V, D
2
= 2 V
D
0
= 0.8 V, D
1
= D
2
= 2 V
D
0
= D
1
= D
2
= 2 V
D
0
= D
1
= D
2
= 0.8 V
V
CC
V
REF
Operating
Operating
V
CC
= 0
→5
V
4.5
0.5
3.35
0.30
—
—
2.0
—
—
—
3.5
1.1
—
—
5.0
—
—
—
—
—
—
—
—
—
—
—
—
—
5.0
—
3.70
0.45
42
12
—
—
<1.0
<-2.0
—
—
—
0
25
—
3.0
—
—
—
0
19.5
38.2
55.5
70.7
83.1
92.4
100
5.5
2.5
4.05
0.60
50
16
—
0.8
20
-200
—
3.1
0.8
±20
55
±5.0
—
±3.0
±4.0
±5.0
—
—
—
—
—
—
—
—
V
V
V
V
mA
mA
V
V
μA
μA
V
V
V
mV
mV
μA
—
%
%
mV
%
%
%
%
%
%
%
%
Continued next page…
* The total error for the V
REF
/V
S
function is the sum of the D/A error and the current-sense comparator input offset voltage.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
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