A3974
DMOS Dual Full-Bridge PWM Motor Driver
Last Time Buy
These parts are in production but have been determined to be
LAST TIME BUY. This classification indicates that the product is
obsolete and notice has been given.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: November 2, 2009
Deadline for receipt of LAST TIME BUY orders: April 30, 2010
Recommended Substitutions:
For existing customer transition, and for new customers or new appli-
cations, refer to the
A3992.
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.
A3974
DMOS Dual Full-Bridge PWM Motor Driver
Features and Benefits
▪
±1.5 A, 50 V continuous output rating
▪
Low r
DS(on)
DMOS output drivers
▪
Programmable slow, fast, and mixed current-decay modes
▪
Serial-interface controls chip functions
▪
Synchronous rectification for low power dissipation
▪
Internal UVLO and thermal shutdown circuitry
▪
Crossover-current protection
▪
Sleep and idle modes
Description
Designed for pulse width modulated (PWM) current control
of two DC motors, the A3974 is capable of output currents to
±1.5 A and operating voltages to 50 V. Internal fixed off-time
PWM current-control timing circuitry can be programmed via
a serial interface to operate in slow, fast, and mixed current-
decay modes.
Independent ENABLE input terminals are provided for use
in controlling the speed and torque of each DC motor with
externally applied PWM control signals.
Synchronous rectification circuitry allows the load current
to flow through the low
r
DS(on)
of the DMOS output driver
during the current decay. This feature will eliminate the need
for external clamp diodes in most applications, saving cost
and external component count, while minimizing power
dissipation.
Internal circuit protection includes thermal shutdown with
hysteresis, undervoltage monitoring of V
DD
and the charge
pump, and crossover-current protection. Special power-up
sequencing is not required.
Package: 44-pin PLCC with internally
fused pins (suffix ED)
Not to scale
The A3974 is supplied in a 44-pin plastic PLCC with 3 internally
fused pins on each side, for maximum heat dissipation. The fused
pins are at ground potential and need no electrical isolation.
Pin-out Diagram
LOAD
43
SUPPLY
1
SENSE
1
OUT
1A
ENABLE
1
GND
GND
GND
NC
OUT
1B
40
NC
NC
41
44
V
BB1
NC
STROBE
CLOCK
7
39
NC
CP2
CP1
CP
GND
GND
GND
OSC
SLEEP
V
REG
NC
42
2
4
6
5
3
1
CHARGE PUMP
SERIAL PORT
8
9
38
37
36
35
34
33
32
PROGRAM
PWM TIMER
LOGIC
DATA
10
GND
11
GND
12
GND
13
REF
1
14
REF
2
15
LOGIC
16
SUPPLY
NC
17
V
DD
PROGRAM
PWM TIMER
LOGIC
31
30
29
V
BB2
OUT
2A
18
NC
20
21
GND
22
23
GND
24
25
ENABLE
2
26
NC
19
SENSE
2
LOAD
SUPPLY
2
OUT
2B
28
GND
NC
27
Dwg. PP-073
29319.35C
A3974
DMOS Dual Full-Bridge PWM Motor Driver
Selection Guide
Part Number
A3974SED-T
A3974SEDTR-T
Packing
27 pieces per tube
450 pieces per reel
Absolute Maximum Ratings
Characteristic
Load Supply Voltage
Logic Supply Voltage
Logic Input Voltage Range
Reference Voltage
Sense Voltage (DC)
Symbol
V
BB
V
DD
V
IN
V
REF
V
S
Continuous
Pulsed, t
w
< 1
μs
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.
Range S
Continuous
Pulsed, t
w
< 30 ns
Notes
Rating
50
7.0
–0.3 to V
DD
+ 0.3
–1.0 to V
DD
+ 1.0
3
0.5
2.5
Units
V
V
V
V
V
V
V
Output Current
I
OUT
±1.5
A
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
T
A
T
J
(max)
T
stg
–20 to 85
150
–55 to 150
ºC
ºC
ºC
Thermal Characteristics
may require derating at maximum conditions, see application information
Characteristic
Package Thermal Resistance
Symbol
R
θJA
R
θJT
Test Conditions*
4-layer PCB based on JEDEC standard
Value Units
22
6
ºC/W
ºC/W
*Additional thermal information available on the Allegro website.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A3974
DMOS Dual Full-Bridge PWM Motor Driver
FUNCTIONAL BLOCK DIAGRAM
V
DD
LOGIC
SUPPLY
CHARGE PUMP
BANDGAP
V
DD
C
REG
TSD
V
BB1
+
CP2
LOAD
SUPPLY
1
BANDGAP
REGULATOR
V
REG
CP1
UNDER-
VOLTAGE &
FAULT DETECT
CHARGE
PUMP
CONTROL LOGIC
PHASE
SYNC RECT MODE
SYNC RECT DISABLE
MODE
CP
OUT
1A
GATE DRIVE
ENABLE
1
OUT
1B
SENSE
1
C
S1
ZERO CURRENT DETECT
FIXED OFF
PROGRAMMABLE
BLANK
DECAY
R
S1
PWM TIMER
OSC
CLOCK
DATA
STROBE
CURRENT SENSE
SERIAL
PORT
REFERENCE
BUFFER &
DIVIDER
REF
1
LOAD
SUPPLY
2
V
REF
V
BB2
FIXED OFF
PROGRAMMABLE
BLANK
DECAY
PWM TIMER
CHARGE
PUMP
+
ENABLE
2
GATE DRIVE
SLEEP
MODE
PHASE
ENABLE
SYNC RECT MODE
SYNC RECT DISABLE
PWM MODE INT
PWM MODE EXT
OUT
2A
OUT
2B
SENSE
2
CONTROL LOGIC
TO PWM TIMER
C
S2
ZERO CURRENT DETECT
R
S2
CURRENT SENSE
REFERENCE
BUFFER &
DIVIDER
REF
2
V
REF2
Dwg. FP-048-1
Copyright © 2001 Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A3974
DMOS Dual Full-Bridge PWM Motor Driver
ELECTRICAL CHARACTERISTICS at T
A
= +25°C, V
BB
= 50 V, V
DD
= 5.0 V, f
PWM
< 50 kHz (unless
otherwise noted).
Characteristic
Output Drivers
Load Supply Voltage Range
Output Leakage Current
Output ON Resistance
Body Diode Forward Voltage
Load Supply Current
V
BB
I
DSS
r
DS(on)
V
F
I
BB
Operating
During sleep mode
V
OUT
= V
BB
V
OUT
= 0 V
Source driver, I
OUT
= -1.5 A
Sink driver, I
OUT
= 1.5 A
Source diode, I
F
= 1.5 A
Sink diode, I
F
= 1.5 A
f
PWM
< 50 kHz
Charge pump on, outputs disabled
Sleep or idle mode
Control Logic
Logic Supply Voltage Range
Logic Input Voltage
Logic Input Current
(except ENABLE)
ENABLE Input Current
V
DD
V
IN(1)
V
IN(0)
I
IN(1)
I
IN(0)
I
EN(1)
I
EN(0)
OSC Input Frequency
OSC Input Duty Cycle
OSC Input Hysterisis
Reference Input Voltage Range
f
OSC
—
ΔV
IN
V
REF
Operating
V
IN
= 2.0 V
V
IN
= 0.8 V
V
EN
= 2.0 V
V
EN
= 0.8 V
Operating
4.5
2.0
—
—
—
—
—
2.9
40
200
0
5.0
—
—
<1.0
<1.0
40
16
—
—
—
—
5.5
—
0.8
±20
±20
100
30
6.1
60
400
2.6
V
V
V
μA
μA
μA
μA
MHz
%
mV
V
15
0
—
—
—
—
—
—
—
—
—
—
—
<1.0
<-1.0
0.5
0.315
—
—
4.0
2.0
—
50
50
20
-20
0.55
0.35
1.2
1.2
7.0
5.0
20
V
V
μA
μA
Ω
Ω
V
V
mA
mA
μA
Symbol
Test Conditions
Min.
Limits
Typ. Max.
Units
continued next page ...
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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