a4973
Full-Bridge PWM Motor Driver
Features anD BeneFits
▪ ±1.5 A continuous output current
▪ 50 V output voltage rating
▪ 3 to 5.5 V logic supply voltage
▪ Internal PWM current control
▪ Fast and slow current decay modes
▪ Sleep (low current consumption) mode
▪ Internal transient-suppression diodes
▪ Internal thermal shutdown circuitry
▪ Crossover current and UVLO protection
Designed for bidirectional pulse-width-modulated (PWM)
current control of inductive loads, the A4973 is capable of
continuous output currents to ±1.5 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.
With the ENABLE input held low, the PHASE input controls
load current polarity by selecting the appropriate source and
sink driver pair. The MODE input determines whether the
PWM current control circuitry operates in a slow current decay
mode (only the selected source driver switching) or in a fast
current decay mode (selected source and sink switching). 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. A sleep mode is
provided to reduce power consumption.
Continued on the next page…
Description
packages:
Package B, 16-pin DIP
with exposed tabs
Not to scale
Package LB, 16-pin SOIC
with internally fused pins
Functional Block Diagram
LOAD
SUPPLY
LOAD
SUPPLY
16
OUT A
LOGIC
SUPPLY
6
V
CC
SLEEP &
STANDBY MODES
9
10
15
MODE
14
V
BB
PHASE
7
UVLO
& TSD
ENABLE
8
BRAKE
1
INPUT LOGIC
Q
BLANKING
S
GROUND
4
5
V
CC
RC
3
CT
+ –
2
V TH
RT
4973DS, Rev. 3
MCO-0000192
–
R
+
PWM LATCH
OUT B
11
2
SENSE
RS
12
REF
13
GROUND
January 8, 2018
A4973
Full-Bridge PWM Motor Driver
Description (continueD)
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 used to dynamically brake brush DC motors.
The A4973 is supplied in a choice of two power packages: a
16-pin dual in-line plastic package with copper heat-sink tabs,
and a 16-pin plastic SOIC with copper heat-sink tabs. For both
package styles, the power tab is at ground potential and needs no
electrical isolation. Each package type is available in a lead (Pb)
free version (100% matte-tin-plated leadframe).
selection guiDe
part number
A4973SB-T *
A4973SLBTR-T
package
16-pin DIP with exposed thermal tabs
16-pin SOICW with internally-fused pins
packing
25 pieces per tube
1000 pieces per reel
* A4973SB-T
is in production but have been determined to be LAST TIME BUY. This classification indicates that the product is obso-
lete and notice has been given. Sale of this device is currently restricted to existing customer applications. The device should not be
purchased for new design applications because of obsolescence in the near future. Samples are no longer available. Date of status
change: December 14, 2017. Deadline for receipt of LAST TIME BUY orders: December 1, 2018. For existing customer transition,
and for new customers or new applications, use A4973SLBTR-T.
aBsolute MaxiMuM ratings
characteristic
Load Supply Voltage
Logic Supply Voltage
Logic/Reference Input Voltage Range
Sense Voltage
Output Current, Continuous
Transient Output Current
Package Power Dissipation
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
symbol
V
BB
V
CC
V
IN
V
SENSE
I
OUT
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.
t
W
< 2 µs
notes
rating
50
6
–0.3 to 6
0.5
±1.5
6
See graph (p. 3)
–20 to 85
150
–55 to 150
units
V
V
V
V
A
A
W
°C
°C
°C
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4973
Full-Bridge PWM Motor Driver
therMal characteristics
characteristic
Package Thermal Resistance, Junction to Ambient
Package Thermal Resistance, Junction to Tab
symbol
R
θJA
R
θJT
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
°C/W
°C/W
°C/W
*Additional thermal information available on Allegro website.
ALLOWABLE PACKAGE POWER DISSIPATION (W)
4
R
θJT
= 6.0°C/W
3
2
SUFFIX 'B', R
θJA
= 43°C/W
1
SUFFIX 'LB', R
θJA
= 67°C/W
0
25
50
75
100
TEMPERATURE IN °C
125
150
pinout DiagraM
LOAD
SUPPLY
OUTB
MODE
GROUND
GROUND
SENSE
OUTA
LOAD
SUPPLY
Dwg. PP-056
BRAKE
1
2
3
4
5
6
7
8
V
CC
V
BB
16
15
14
13
Note the A4973SB (DIP) and
the A4973SLB (SOIC) are
electrically identical and share
a common terminal number
assignment.
REF
RC
GROUND
GROUND
LOGIC
SUPPLY
PHASE
ENABLE
LOGIC
12
11
10
V
BB
9
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4973
Full-Bridge PWM Motor Driver
electrical characteristics: Valid at t
J
= 25°c, V
cc
= 3.0 to 5.5 V, unless otherwise noted
characteristic
power outputs
Load Supply Voltage Range
Output Leakage Current
Output On Resistance
ac tiMing
PWM RC Fixed Off-time
PWM Minimum On Time
Crossover Dead Time
Maximum PWM Frequency
control circuitry
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
UVLO Enable Threshold
UVLO Hysteresis
Logic Supply Current
Motor Supply Current (No Load)
Logic Supply Voltage Range
T
J
∆T
J
V
UVLO
∆V
UVLO
I
CC(ON)
I
CC(Sleep)
I
BB(ON)
I
BB(Sleep)
V
CC
V
IN(1)
Logic Input Voltage
V
IN(0)
Logic Input Current
Reference Input Current
Comparator Input Offset Volt.
Reference Input Voltage Range
Gain
I
IN(1)
I
IN(0)
I
REF
V
IO
V
REF
A
V
V
IN
= V
CC
= 5 V
V
IN
= 0 V, V
CC
= 5 V
V
REF
= 0 V to 1 V
V
REF
= 0 V
REF Pin
V
REF
= 1 V
V
ENABLE
= V
IN(0)
, V
BRAKE
= V
IN(1)
V
ENABLE
= V
MODE
= V
BRAKE
= V
IN(1)
V
ENABLE
= V
IN(0)
V
ENABLE
= V
MODE
= V
BRAKE
= V
IN(1)
Operating
–
–
2.5
0.12
–
–
–
–
3.0
V
CC
×
0.55
–
—
—
–
–
0
1.9
165
15
2.75
0.17
2.7
250
500
<1.0
5.0
–
–
0
–106
–
±2.0
–
2
–
–
3.0
0.25
3.5
450
700
3
5.5
–
V
CC
×
0.27
–10
–200
±5.0
±5.0
1
2.1
°C
°C
V
V
mA
µA
µA
µA
V
V
V
µA
µA
µA
mV
V
–
t
OFF RC
t
ON(min)
t
CODT
f
PWM(max)
I
OUT
= 1.5 A
C
T
= 680 pF, R
T
= 30 kΩ, V
CC
= 3.3 V
V
CC
= 3.3 V, R
T
≥ 12 kΩ, C
T
= 680 pF
V
CC
= 5.0 V, R
T
≥ 12 kΩ, C
T
= 470 pF
18.3
0.8
0.8
–
70
20.4
1.4
1.6
500
–
22.5
1.9
2.0
–
–
µs
µs
µs
ns
kHz
V
BB
I
CEX
R
DS(on)
Operating
V
OUT
= V
BB
V
OUT
= 0 V
Total sink and source, I
OUT
= 1.5 A, V
BB
> 8 V, T
J
= 25°C
5
–
–
–
–
<1.0
<–1.0
1
50
50
–50
1.4
V
µA
µA
Ω
symbol
test conditions
Min.
typ.
Max.
unit
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4973
Functional Description
internal pwM current control During Forward
and reverse operation.
The A4973 contains a fixed off-
Full-Bridge PWM Motor Driver
The user selects an external resistor (R
T
) and capacitor (C
T
) to
determine the time period (t
OFF
= R
T
× C
T
) during which the
drivers remain disabled (see RC Fixed Off-Time section, below).
At the end of the RC interval, the drivers are enabled allow-
ing the load current to increase again. The PWM cycle repeats,
maintaining the peak load current at the desired value (figure 2).
time pulse-width-modulated (PWM) current control circuit that
can be used to limit the load current to a desired value. The peak
value of the current limiting (I
TRIP
) is set by the selection of an
external current sensing resistor (R
S
) and reference input volt-
age (V
REF
). The internal circuitry compares the voltage across
the external sense resistor to the voltage on the reference input
terminal (REF) resulting in a transconductance function approxi-
mated by:
I
TRIP
≈
V
REF
2
×
R
S
Figure 2
Fast and slow current Decay waveforms
ENABLE
MODE
In forward or reverse mode, the current control circuitry limits
the load current as follows: when the load current reaches I
TRIP
,
the comparator resets a latch that turns off the selected source
driver or selected sink and source driver pair depending on
whether the device is operating in slow or fast current decay
mode, respectively.
In slow current decay mode, the selected source driver is dis-
abled and both sinks are turned on. The load inductance causes
the current to recirculate through the sink drivers. In fast current
decay mode, the selected sink and source driver pair are dis-
abled, then the opposite pair is turned on. The load inductance
causes the current to flow from ground to the load supply via the
motor winding and the opposite pair of transistors (see figure 1).
I
TRIP
LOAD
CURRENT
RC
RC
Dwg. WP-015-1
Brake operation.
During braking, care should be taken to
Figure 1 — load-current paths
V
BB
ensure that the motor’s current does not exceed the ratings of the
device. The braking current can be measured by using an oscillo-
scope with a current probe connected to one of the motor’s leads,
or if the back-EMF voltage of the motor is known, approximated
by:
I
PEAK BRAKE ML
≈
V
BEMF
R
LOAD
cuitry uses a one-shot to control the time the driver(s) remain(s)
off. The one-shot time, t
OFF
(fixed off-time), is determined by the
selection of an external resistor (R
T
) and capacitor (C
T
) con-
nected in parallel from the RC timing terminal to ground. The
fixed off-time, over a range of values of C
T
= 470 pF to 1500 pF
and R
T
= 12 kΩ to 100 kΩ, is approximated by:
rc Fixed off-time.
The internal PWM current control cir-
R
S
Drive Current (Normal)
Recirculation (Fast Decay)
Recirculation (Slow Decay)
t
OFF
≈ R
T
x C
T
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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