3951
Data Sheet
29319.4
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage, V
BB
................... 50 V
Output Current, I
OUT
(t
w
20 s) ..................................
3.5 A
(Continuous) ...............................
2.0 A
Logic Supply Voltage, V
CC
.................. 7.0 V
Logic Input Voltage Range,
V
IN
........................ -0.3 V to V
CC
+ 0.3 V
Sense Voltage, V
SENSE
........................ 1.5 V
Reference Voltage, V
REF
....................... V
CC
Package Power Dissipation,
P
D
....................................... See Graph
Operating Temperature Range,
T
A
............................... 20
C to +85
C
Junction Temperature, T
J
............. +150
C*
Storage Temperature Range,
T
S
............................. 55
C to +150
C
Output current rating may be limited by duty cycle,
ambient temperature, heat sinking and/or forced
cooling. 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 device thermal shutdown
circuitry. These conditions can be tolerated but
should be avoided.
A3951SB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
GROUND
GROUND
GROUND
LOGIC
SUPPLY
PHASE
GROUND
GROUND
RC
SENSE
LOAD
SUPPLY
Dwg. PP-056-1
REF/
LOAD
SUPPLY
V
CC
OUTB
OUTA
V
BB
V
BB
LOGIC
ENABLE
BRAKE
NC
Designed for bidirectional pulse-width modulated current control of
inductive loads, the A3951SB and A3951SW are capable of continuous
output currents to
2 A and operating voltages to 50 V. Internal fixed
off-time PWM current-control circuitry can be used to regulate the
maximum load current to a desired value. The peak load current limit is
set by the user's selection of an input reference voltage and external
sensing resistor. The fixed off-time pulse duration is set by a user-
selected external RC timing network. Internal circuit protection includes
thermal shutdown with hysteresis, transient suppression diodes, and
crossover-current protection. Special power-up sequencing is not
required. The A3951SB and A3951SW are improved replacements for
the UDN2953B and UDN2954W, respectively. For new system de-
signs, the A3952SB/SEB/SLB/SW are recommended.
With the ENABLE input held low, the PHASE input controls load
current polarity by selecting the appropriate source and sink driver pair.
A user-selectable blanking window prevents false triggering of the PWM
current control circuitry. With the ENABLE input held high, all output
drivers are disabled.
When a logic low is applied to the BRAKE input, the braking
function is enabled. This overrides ENABLE and PHASE to turn off
both source drivers and turn on both sink drivers. The brake function
can be safely used to dynamically brake brush dc motors.
The A3951SB is supplied in a 16-pin dual in-line plastic package
with copper heat-sink contact tabs. The lead configuration enables
easy attachment of a heat sink while fitting a standard printed wiring
board layout. The A3951SW, for higher package power dissipation
requirements, is supplied in a 12-pin single in-line power-tab package.
In either package style, the batwing/power tab is at ground potential
and needs no isolation.
FEATURES
I 2 A Continuous Output Current Rating
I 50 V Output Voltage Rating
I Internal PWM Current Control
I Internal Transient Suppression Diodes
I Under-Voltage Lockout
I Internal Thermal Shutdown Circuitry
I Crossover-Current Protection
I Default Brake Current Limit
Always order by complete part number:
Part Number
Package
R
JA
R
JT
A3951SB
16-Pin DIP
43
C/W
6.0
C/W
A3951SW
12-Pin Power-Tab SIP
36
C/W
2.0
C/W
FULL-BRIDGE PWM MOTOR DRIVER
3951
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
2
V
BB
RC
LOAD
SUPPLY
PHASE
UVLO
& TSD
R S
Dwg. FP-036-1
REF/
OUT
A
OUT
B
ENABLE
SENSE
+
BRAKE
9R
R
INPUT LOGIC
GROUND
Q
R
S
1.5 V
PWM LATCH
V
CC
+
BLANKING
VTH
V
CC
LOGIC
SUPPLY
50
75
100
125
150
10
6
4
2
0
TEMPERATURE IN
C
8
25
Dwg. GP-032A
SUFFIX 'B', R = 43
C/W
JA
SUFFIX 'W', R = 38
C/W
JA
SUFFIX 'W',
R = 2.0
C/W
JT
SUFFIX 'B',
R = 6.0
C/W
JT
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
TRUTH TABLE
BRAKE ENABLE PHASE
OUT
A
OUT
B
DESCRIPTION
H
H
X
Z
Z
Outputs Disabled
H
L
H
H
L
Forward
H
L
L
L
H
Reverse
L
X
X
L
L
Brake, See Note
X = Irrelevant
Z = High Impedance (source and sink both off)
NOTE: Includes internal default V
sense
level for over-current protection.
Copyright 1994, 2000 Allegro MicroSystems, Inc.
FUNCTIONAL BLOCK DIAGRAM
3951
FULL-BRIDGE
PWM MOTOR DRIVER
3
www.allegromicro.com
1
2
3
4
5
6
7
8
9
10
11
12
GROUND
Dwg. PP-058-1
LOGIC
SUPPLY
PHASE
RC
SENSE
REF/
LOAD
SUPPLY
OUT
B
OUT
A
ENABLE
V
CC
V
BB
LOGIC
BRAKE
LOAD
SUPPLY
NC
Continued next page ...
A3951SW
ELECTRICAL CHARACTERISTICS at T
A
= +25
C, V
BB
= 50 V, V
CC
= 5.0 V,
V
REF
= 2.0 V, V
SENSE
= 0 V, RC = 20 k
/1000 pF to Ground (unless noted otherwise).
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Output Drivers
Load Supply Voltage Range
V
BB
Operating, I
OUT
=
2.0 A, L = 3 mH
V
CC
50
V
Output Leakage Current
I
CEX
V
OUT
= V
BB
<1.0
50
A
V
OUT
= 0 V
<-1.0
-50
A
Output Saturation Voltage
V
CE(SAT)
Source driver, I
OUT
= -0.5 A
0.9
1.2
V
Source driver, I
OUT
= -1.0 A
1.0
1.4
V
Source driver, I
OUT
= -2.0 A
1.2
1.8
V
Sink driver, I
OUT
= +0.5 A
0.9
1.2
V
Sink driver, I
OUT
= +1.0 A
1.0
1.4
V
Sink driver, I
OUT
= +2.0 A
1.3
1.8
V
Clamp Diode Forward Voltage
V
F
I
F
= 0.5 A
1.0
1.4
V
(Source or Sink)
I
F
= 1.0 A
1.1
1.6
V
I
F
= 2.0 A
1.4
2.0
V
Load Supply Current
I
BB(ON)
V
ENABLE
= 0.8 V, V
REF
= 2.0 V
2.9
6.0
mA
(No Load)
I
BB(OFF)
V
ENABLE
= V
REF
= 2.0 V
3.1
6.5
mA
I
BB(BRAKE)
V
BRAKE
= 0.8 V
3.1
6.5
mA
3951
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
4
Control Logic
Logic Supply Voltage Range
V
CC
Operating
4.5
5.0
5.5
V
Logic Input Voltage
V
IN(1)
2.0
V
V
IN(0)
0.8
V
Logic Input Current
I
IN(1)
V
IN
= 2.0 V
<1.0
20
A
I
IN(0)
V
IN
= 0.8 V
<-2.0
-200
A
Reference Voltage Range
V
REF
Operating
2.0
V
CC
V
Reference Input Current
I
REF
2.0 V
V
REF
V
CC
25
40
55
A
Reference Voltage Divider Ratio
V
REF
= 5 V
9.5
10.0
10.5
PWM RC Fixed Off Time
t
off
C
T
= 1000 pF, R
T
= 20 k
18
20
22
s
PWM Minimum On Time
t
on(min)
C
T
= 820 pF, R
T
12 k
1.7
3.0
s
C
T
= 1200 pF, R
T
12 k
2.5
3.8
s
Propagation Delay Time
t
pd
I
OUT
=
2.0 A, 50% E
IN
to 90% E
OUT
transition:
ENABLE on to source driver on
2.9
s
ENABLE off to source driver off
0.7
s
ENABLE on to sink driver on
2.4
s
ENABLE off to sink driver off
0.7
s
PHASE change to source driver on
2.9
s
PHASE change to source driver off
0.7
s
PHASE change to sink driver on
2.4
s
PHASE change to sink driver off
0.7
s
t
pd(pwm)
Comparator trip to sink driver off
0.8
1.5
s
Thermal Shutdown Temperature
T
J
165
C
Thermal Shutdown Hysteresis
T
J
15
C
UVLO Disable Threshold
V
CC(UVLO)
3.15
3.50
3.85
V
UVLO Hysteresis
V
CC(UVLO)
300
400
500
mV
Logic Supply Current
I
CC(ON)
V
ENABLE
= 0.8 V, V
REF
= 2.0 V
20
30
mA
(No Load)
I
CC(OFF)
V
ENABLE
= V
REF
= 2.0 V
12
18
mA
I
CC(BRAKE)
V
REF
= 0.8 V
26
40
mA
NOTES: 1. Typical Data is for design information only.
2. Each driver is tested separately.
3. Negative current is defined as coming out of (sourcing) the specified device terminal.
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
ELECTRICAL CHARACTERISTICS (Continued)
3951
FULL-BRIDGE
PWM MOTOR DRIVER
5
www.allegromicro.com
FUNCTIONAL DESCRIPTION
INTERNAL PWM CURRENT CONTROL DURING
FORWARD AND REVERSE OPERATION
The A3951SB/SW contain a fixed off-time pulse-width
modulated (PWM) current-control circuit that can be used
to limit the load current to a desired value. The value of
the current limiting (I
TRIP
) is set by the selection of an
external current sensing resistor (R
S
) and reference input
voltage (V
REF
). The internal circuitry compares the
voltage across the external sense resistor to one tenth the
voltage on the REF input terminal, resulting in a function
approximated by
I
TRIP
= V
REF
/(10R
S
).
In forward or reverse mode the current-control cir-
cuitry limits the load current. When the load current
reaches I
TRIP
, the comparator resets a latch to turn off the
selected sink driver. The load inductance causes the
current to recirculate through the source driver and
flyback diode (two-quadrant operation or slow decay).
See figure 1.
Figure 1 -- Load-Current Paths
The user selects an external resistor (R
T
) and capaci-
tor (C
T
) to determine the time period (t
off
= R
T
C
T
) during
which the drivers remain disabled (see "RC Fixed OFF
Time" below). At the end of the R
T
C
T
interval, the drivers
are re-enabled allowing the load current to increase again.
The PWM cycle repeats, maintaining the load current at
the desired value (see figure 2).
Dwg. EP-006-9
R S
BB
V
DRIVE CURRENT
RECIRCULATION
ENABLE
LOAD
CURRENT
RC
I
TRIP
Dwg. WP-015-3
Figure 2 -- Load-Current Waveform
INTERNAL PWM CURRENT CONTROL DURING
BRAKE MODE OPERATION
The brake circuit turns off both source drivers and
turns on both sink drivers. For dc motor applications, this
has the effect of shorting the motor's back-EMF voltage,
resulting in current flow that brakes the motor dynamically.
However, if the back-EMF voltage is large and there is no
PWM current limiting, then the load current can increase to
a value that approaches a locked rotor condition. To limit
the current, when the I
TRIP
level is reached, the PWM
circuit disables the conducting sink driver. The energy
stored in the motor's inductance is then discharged into
the load supply causing the motor current to decay.
As in the case of forward/reverse operation, the drivers
are re-enabled after a time given by t
off
= R
T
C
T
(see "RC
Fixed Off Time" below). Depending on the back-EMF
voltage (proportional to the motor's decreasing speed), the
load current again may increase to I
TRIP
. If so, the PWM
cycle will repeat, limiting the load current to the desired
value.
Brake Operation
During braking, the peak current limit defaults inter-
nally to a value approximated by
I
TRIP
= 1.5 V/R
S
.
In this mode, the value of R
S
determines the I
TRIP
value
independent of V
REF
. This is useful in applications with
differing run and brake currents and no practical method of
varying V
REF
.
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