Data Sheet
29319.1*
FULL-BRIDGE PWM MOTOR DRIVER
Designed for bidirectional pulse-width modulated current control of
inductive loads, the A3952S– is 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.
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 sink 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 when inactive.
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 A3952S– is supplied in a choice of four power packages. In all
package styles, the batwing/power tab is at ground potential and needs
no isolation. These devices are also available for operation from -40°C
to +125°C. To order, change the suffix from 'S–' to 'K–'.
FEATURES
■±2 A Continuous Output Current Rating
■50 V Output Voltage Rating
■Internal PWM Current Control
■Fast and Slow Current-Decay Modes
■Sleep (Low Current Consumption) Mode
■Internal Transient Suppression Diodes
■Under-Voltage Lockout
■Internal Thermal Shutdown Circuitry
■Crossover-Current Protection
Always order by complete part number:
Part Number Package RθJA RθJT
A3952SB 16-Pin DIP 43°C/W 6.0°C/W
A3952SEB 28-Lead PLCC 42°C/W 6.0°C/W
A3952SLB 16-Lead SOIC 67°C/W 6.0°C/W
A3952SW 12-Pin Power-Tab SIP 36°C/W 2.0°C/W
A3952SB
Note that the A3952SB (DIP) and the A3952SLB
(SOIC) are electrically identical and share a
common terminal number assignment.
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage, VBB .................. 50 V
Output Current, IOUT
(tw ≤ 20 µs).................................. ±3.5 A
(Continuous) ............................... ±2.0 A
Logic Supply Voltage, VCC ................. 7.0 V
Logic Input Voltage Range,
VIN ....................... -0.3 V to VCC + 0.3 V
Sense Voltage, VSENSE ...................... 1.5 V
Reference Voltage, VREF .................... 15 V
Package Power Dissipation,
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, 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.
3952
MODE
GROUND
GROUND
LOGIC
SUPPLY
PHASE
GROUND
GROUND
RC
SENSE
LOAD
SUPPLY
Dwg. PP-056
BRAKE
REF
LOAD
SUPPLY
V
CC
OUTB
OUTA
V
BB
V
BB
LOGIC
ENABLE
1
2
3
4
5
6
7
89
10
11
12
13
14
15
16
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
V
BB
RC
V
CC
LOGIC
SUPPLY
LOAD
SUPPLY
PHASE
EMITTERS
UVLO
& TSD
RS
Dwg. FP-036
MODE
REF
OUTA
OUTB
ENABLE
SENSE
–
+
BRAKE
9R
R
INPUT LOGIC
GROUND
QR
S
1.5 V
PWM LATCH
V
CC
+ –
BLANKING
SLEEP &
STANDBY MODES
VTH
'EB' ONLY
'B', 'LB', & 'W'
PACKAGES
RT
CT
FUNCTIONAL BLOCK DIAGRAM
TRUTH TABLE
BRAKE ENABLE PHASE MODE OUTAOUTBDESCRIPTION
H H X H Z Z Sleep Mode
H H X L Z Z Standby, Note 1
H L H H H L Forward,
Fast-Decay Mode
H L H L H L Forward,
Slow-Decay Mode
H L L H L H Reverse,
Fast-Decay Mode
H L L L L H Reverse,
Slow-Decay Mode
L X X H L L Brake,
Fast-Decay Mode
L X X L L L Brake, No Current
Control, Note 2
X = Irrelevant Z = High Impedance (source and sink both OFF)
NOTES: 1. Includes active pull-offs for power outputs.
2. Includes internal default Vsense level for over-current protection.
50 75 100 125 150
10
6
4
2
0
TEMPERATURE IN °C
8
25
Dwg. GP-007-1A
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
'W' TAB
'B' , 'EB', & 'LB' TAB
'W' AMBIENT
'B' & 'EB' AMBIENT
'LB' AMBIENT
Copyright © 1994 Allegro MicroSystems, Inc.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
A3952SEB A3952SW
ELECTRICAL CHARACTERISTICS at TA = +25°C, VBB = 50 V, VCC = 5.0 V, VBRAKE = 2.0 V,
VSENSE = 0 V, RC = 20 kΩ/1000 pF to Ground (unless noted otherwise).
Limits
Characteristic Symbol Test Conditions Min. Typ. Max. Units
Output Drivers
Load Supply Voltage Range VBB Operating, IOUT = ±2.0 A, L = 3 mH VCC –50 V
Output Leakage Current ICEX VOUT = VBB –<1.0 50 µA
VOUT = 0 V –<-1.0 -50 µA
Output Saturation Voltage VCE(SAT) Source Driver, IOUT = -0.5 A –0.9 1.2 V
Source Driver, IOUT = -1.0 A –1.0 1.4 V
Source Driver, IOUT = -2.0 A –1.2 1.8 V
Sink Driver, IOUT = +0.5 A –0.9 1.2 V
Sink Driver, IOUT = +1.0 A –1.0 1.4 V
Sink Driver, IOUT = +2.0 A –1.3 1.8 V
Clamp Diode Forward Voltage VFIF = 0.5 A –1.0 1.4 V
(Source or Sink) IF = 1.0 A –1.1 1.6 V
IF = 2.0 A –1.4 2.0 V
Load Supply Current IBB(ON) VENABLE = 0.8 V –2.9 6.0 mA
(No Load) IBB(OFF) VENABLE = 2.0 V, VMODE = 0.8 V –3.1 6.5 mA
VBRAKE = 0.8 V –3.1 6.5 mA
IBB(SLEEP) VENABLE = VMODE = 2.0 V –<1.0 50 µA
12345 6789101112
GROUND
Dwg. PP-058
MODE
LOGIC
SUPPLY
PHASE
RC
SENSE
REF
LOAD
SUPPLY
OUTB
OUTA
ENABLE
V
CC
V
BB
LOGIC
BRAKE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
GROUND
GROUND GROUND
GROUND
Dwg. PP-057
NO
CONNECTION
EMITTERS
RC
LOAD
SUPPLY
REF
V
CC
V
BB
LOGIC
BRAKE
LOGIC
SUPPLY
PHASE
ENABLE
MODE
SENSE
LOAD
SUPPLY
OUTB
OUTA
Continued next page …
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Control Logic
Logic Supply Voltage Range VCC Operating 4.5 5.0 5.5 V
Logic Input Voltage VIN(1) 2.0 ––V
VIN(0) ––0.8 V
Logic Input Current IIN(1) VIN = 2.0 V –<1.0 20 µA
IIN(0) VIN = 0.8 V –<-2.0 -200 µA
Reference Voltage Range VREF Operating 0 –15 V
Reference Input Current IREF VREF = 2.0 V 25 40 55 µA
Reference Voltage Divider Ratio –VREF = 15 V 9.5 10.0 10.5 –
Comparator Input Offset Voltage VIO VREF = 0 V –±1.0 ±10 mV
PWM RC Fixed OFF Time toff CT = 1000 pF, RT = 20 kΩ18 20 22 µs
PWM Minimum ON Time ton(min) CT = 820 pF, RT ≥ 12 kΩ–1.7 3.0 µs
CT = 1200 pF, RT ≥ 12 kΩ–2.5 3.8 µs
Propagation Delay Time tpd IOUT = ±2.0 A, 50% EIN to 90% EOUT Transition:
ENABLE ON to Source ON –2.9 –µs
ENABLE OFF to Source OFF –0.7 –µs
ENABLE ON to Sink ON –2.4 –µs
ENABLE OFF to Sink OFF –0.7 –µs
PHASE Change to Source ON –2.9 –µs
PHASE Change to Source OFF –0.7 –µs
PHASE Change to Sink ON –2.4 –µs
PHASE Change to Sink OFF –0.7 –µs
tpd(pwm) Comparator Trip to Sink OFF –0.8 1.5 µs
Thermal Shutdown Temperature TJ–165 –°C
Thermal Shutdown Hysteresis ∆TJ–15 –°C
UVLO Disable Threshold VCC(UVLO) 3.15 3.50 3.85 V
UVLO Hysteresis ∆VCC(UVLO) 300 400 500 mV
Logic Supply Current ICC(ON) VENABLE = 0.8 V, VBRAKE = 2.0 V –20 30 mA
(No Load) ICC(OFF) VENABLE = 2.0 V, VMODE = 0.8 V –12 18 mA
ICC(BRAKE) VBRAKE = 0.8 V –26 40 mA
ICC(SLEEP) VENABLE = VMODE = VBRAKE = 2.0 V –3.0 5.0 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
3952
FULL-BRIDGE
PWM MOTOR DRIVER
FUNCTIONAL DESCRIPTION
INTERNAL PWM CURRENT CONTROL DURING
FORWARD AND REVERSE OPERATION
The A3952S– contains 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 (ITRIP) is set by the selection of an
external current sensing resistor (RS) and reference input
voltage (VREF). 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 approxi-
mated by ITRIP = VREF/(10RS).
In forward or reverse mode the current-control circuitry
limits the load current. When the load current reaches
ITRIP, the comparator resets a latch to turn OFF the
selected sink driver (in the slow-decay mode) or selected
sink and source driver pair (in the fast-decay mode). In
slow-decay mode, the selected sink driver is disabled; the
load inductance causes the current to recirculate through
the source driver and flyback diode (see figure 1). In fast-
decay mode, the selected sink and source driver pair are
disabled; the load inductance causes the current to flow
from ground to the load supply via the ground clamp and
flyback diodes.
Figure 1 — Load-Current Paths
The user selects an external resistor (RT) and capaci-
tor (CT) to determine the time period (toff = RTCT) during
which the drivers remain disabled (see “RC Fixed OFF
Time” below). At the end of the RTCT 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).
ENABLE
MODE
LOAD
CURRENT
RC
I
TRIP
Dwg. WP-015-1
RC
Dwg. EP-006-2A
RS
BB
V
DRIVE CURRENT
RECIRCULATION
(SLOW-DECAY MODE)
RECIRCULATION
(FAST-DECAY MODE)
Figure 2 — Fast and Slow Current-Decay Waveforms
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 ITRIP 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 toff = RTCT (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 ITRIP. If so, the PWM
cycle will repeat, limiting the load current to the desired
value.
Brake Operation - MODE Input High
During braking, when the MODE input is high, the
current limit can be approximated by
ITRIP = VREF/(10RS).
CAUTION: Because the kinetic energy stored in the
motor and load inertia is being converted into current,
which charges the VBB supply bulk capacitance (power
supply output and decoupling capacitance), care must be
taken to ensure the capacitance is sufficient to absorb the
energy without exceeding the voltage rating of any devices
connected to the motor supply.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Brake Operation - MODE Input Low
During braking, with the MODE input low, the peak
current limit defaults internally to a value approximated by
ITRIP = 1.5 V/RS.
In this mode, the value of RS determines the ITRIP value
independent of VREF. This is useful in applications with
differing run and brake currents and no practical method of
varying VREF.
Choosing a small value for RS essentially disables the
current limiting during braking. Therefore, care should be
taken to ensure that the motor’s current does not exceed
the absolute maximum ratings of the device. The braking
current can be measured by using an oscilloscope with a
current probe connected to one of the motor’s leads.
RC Fixed OFF Time
The internal PWM current control circuitry uses a one
shot to control the time the driver(s) remain(s) OFF. The
one shot time, toff (fixed OFF time), is determined by the
selection of an external resistor (RT) and capacitor (CT)
connected in parallel from the RC terminal to ground. The
fixed OFF time, over a range of values of CT = 820 pF to
1500 pF and RT = 12 kΩ to 100 kΩ, is approximated by
toff = RTCT.
When the PWM latch is reset by the current compara-
tor, the voltage on the RC terminal will begin to decay from
approximately 3 volts. When the voltage on the RC
terminal reaches approximately 1.1 volt, the PWM latch is
set, thereby re-enabling the driver(s).
RC Blanking
In addition to determining the fixed OFF-time of the
PWM control circuit, the CT component sets the compara-
tor blanking time. This function blanks the output of the
comparator when the outputs are switched by the internal
current control circuitry (or by the PHASE, BRAKE, or
ENABLE inputs). The comparator output is blanked to
prevent false over-current detections due to reverse
recovery currents of the clamp diodes, and/or switching
transients related to distributed capacitance in the load.
During internal PWM operation, at the end of the toff
time, the comparator’s output is blanked and CT begins to
be charged from approximately 1.1 V by an internal current
source of approximately 1 mA. The comparator output
remains blanked until the voltage on CT reaches approxi-
mately 3.0 volts.
Similarly, when a transition of the PHASE input occurs,
CT is discharged to near ground during the crossover delay
time (the crossover delay time is present to prevent
simultaneous conduction of the source and sink drivers).
After the crossover delay, CT is charged by an internal
current source of approximately 1 mA. The comparator
output remains blanked until the voltage on CT reaches
approximately 3.0 volts.
Similarly, when the device is disabled via the ENABLE
input, CT is discharged to near ground. When the device is
re-enabled, CT is charged by the internal current source.
The comparator output remains blanked until the voltage
on CT reaches approximately 3.0 V.
For applications that use the internal fast-decay mode
PWM operation, the minimum recommended value is CT =
1200 pF ±5 %. For all other applications, the minimum
recommended value is CT = 820 pF ±5 %. These values
ensure that the blanking time is sufficient to avoid false
trips of the comparator under normal operating conditions.
For optimal regulation of the load current, the above
values for CT are recommended and the value of RT can
be sized to determine toff. For more information regarding
load current regulation, see below.
LOAD CURRENT REGULATION WITH THE INTERNAL
PWM CURRENT-CONTROL CIRCUITRY
When the device is operating in slow-decay mode,
there is a limit to the lowest level that the PWM current-
control circuitry can regulate load current. The limitation is
the minimum duty cycle, which is a function of the user-
selected value of toff and the maxuimum value of the
minimum ON-time pulse, ton(min), that occurs each time the
PWM latch is reset. If the motor is not rotating, as in the
case of a stepper motor in hold/detent mode, or a brush dc
motor when stalled or at startup, the worst-case value of
current regulation can be approximated by
I(AV) ≈ [(VBB – VSAT(source+sink)) • ton(min)max] – [1.05 (VSAT(sink) + VD) • toff]
1.05 (ton(min)max + toff) • RLOAD
where toff = RTCT, RLOAD is the series resistance of the
load, VBB is the load/motor supply voltage, and ton(min)max
is specified in the electrical characteristics table. When
the motor is rotating, the back EMF generated will influ-
ence the above relationship. For brush dc motor applica-
tions, the current regulation is improved. For stepper
motor applications when the motor is rotating, the effect is
more complex. A discussion of this subject is included in
the section on stepper motors under “Applications”.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
The following procedure can be used to evaluate the
worst-case slow-decay internal PWM load current regula-
tion in the system:
Set VREF to 0 volts. With the load connected and the PWM
current control operating in slow-decay mode, use an
oscilloscope to measure the time the output is low (sink
ON) for the output that is chopping. This is the typical
minimum ON time (ton(min)typ) for the device. CT then
should be increased until the measured value of ton(min) is
equal to ton(min)max) = 3.0 µs as specified in the electrical
characteristics table. When the new value of CT has been
set, the value of RT should be decreased so the value for
toff = RT•CT (with the artificially increased value of CT) is
equal to 105% of the nominal design value. The worst-
case load current regulation then can be measured in the
system under operating conditions.
In applications utilizing both fast- and slow-decay
internal PWM modes, the performance of the slow-decay
current regulation should be evaluated per the above
procedure and a ton(min)max of 3.8 µs. This corresponds to
a CT value of 1200 pF, which is required to ensure suffi-
cient blanking during fast-decay internal PWM.
LOAD CURRENT REGULATION WITH EXTERNAL
PWM OF THE PHASE AND ENABLE INPUTS
The PHASE and ENABLE inputs can be pulse-width
modulated to regulate load current. Typical propagation
delays from the PHASE and ENABLE inputs to transitions
of the power outputs are specified in the electrical charac-
teristics table. If the internal PWM current control is used,
then the comparator blanking function is active during
phase and enable transitions. This eliminates false
tripping of the over-current comparator caused by switch-
ing transients (see “RC Blanking” above).
ENABLE Pulse-Width Modulation
With the MODE input low, toggling the ENABLE input
turns ON and OFF the selected source and sink drivers.
The corresponding pair of flyback and ground clamp
diodes conduct after the drivers are disabled, resulting in
fast current decay. When the device is enabled, the
internal current control circuitry will be active and can be
used to limit the load current in a slow-decay mode.
For applications that PWM the ENABLE input, and
desire that the internal current limiting circuit function in the
fast-decay mode, the ENABLE input signal should be
inverted and connected to the MODE input. This prevents
the device from being switched into sleep mode when the
ENABLE input is low.
PHASE Pulse-Width Modulation
Toggling the PHASE terminal determines/controls
which sink/source pair is enabled, producing a load current
that varies with the duty cycle and remains continuous at
all times. This can have added benefits in bidirectional
brush dc servo motor applications as the transfer function
between the duty cycle on the phase input and the aver-
age voltage applied to the motor is more linear than in the
case of ENABLE PWM control (which produces a discon-
tinuous current at low current levels). See also, “DC Motor
Applications” below.
SYNCHRONOUS FIXED-FREQUENCY PWM
The internal PWM current-control circuitry of multiple
A3952S– devices can be synchronized by using the simple
circuit shown in figure 3. A 555 IC can be used to gener-
ate the reset pulse/blanking signal (t1) and the period of
the PWM cycle (t2). The value of t1 should be a minimum
of 1.5 µs in slow-decay mode and 2 µs in fast-decay
mode. When used in this configuration, the RT and CT
components should be omitted. The PHASE and ENABLE
inputs should not be PWMed with this circuit configuration
due to the absence of a blanking function synchronous
with their transitions.
Figure 3 — Synchronous Fixed-Frequency Control Circuit
MISCELLANEOUS INFORMATION
A logic high applied to both the ENABLE and MODE
terminals puts the device into a sleep mode to minimize
current consumption when not in use.
An internally generated dead time prevents crossover
currents that can occur when switching phase or braking.
Thermal protection circuitry turns OFF all drivers
should the junction temperature reach 165°C (typical).
This is intended only to protect the device from failures
due to excessive junction temperatures and should not
Dwg. EP-060
100 kΩ
20 kΩ
1N4001
2N2222
V
CC
RC
1
RC
N
t
1
2
t
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
APPLICATION NOTES
The current-sensing comparator functions down to
ground allowing the device to be used in microstepping,
sinusoidal, and other varying current profile applications.
Thermal Considerations
For reliable operation, it is recommended that the
maximum junction temperature be kept as low as possible,
typically 90°C to 125°C. The junction temperature can be
measured by attaching a thermocouple to the power tab/
batwing of the device and measuring the tab temperature,
TT . The junction temperature can then be approximated by
using the formula
TJ ≈ TT + (2 VF IOUT RθJT)
where VF is the clamp diode forward voltage and can be
determined from the electrical specification table for the
given level of IOUT. The value for RθJT is given in the
package thermal resistance table for the appropriate
package.
The power dissipation of the batwing packages can be
improved by 20 to 30% by adding a section of printed circuit
board copper (typically 6 to 18 square centimeters) con-
nected to the batwing terminals of the device.
The thermal performance in applications with high load
currents and/or high duty cycles can be improved by adding
external diodes in parallel with the internal diodes. In
internal PWM slow-decay applications, only the two top-side
(flyback) diodes need be added. For internal fast-decay
PWM, or external PHASE or ENABLE input PWM applica-
tions, all four external diodes should be added for maximum
junction temperature reduction.
imply that output short circuits are permitted. The hyster-
esis of the thermal shutdown circuit is approximately 15°C.
If the internal current-control circuitry is not used; the
VREF terminal should be connected to VCC, the SENSE
terminal should be connected to ground, and the RC
terminal should be left floating (no connection).
An internal under-voltage lockout circuit prevents
simultaneous conduction of the outputs when the device is
powered up or powered down.
Current Sensing
The actual peak load current (IOUTP) will be greater
than the calculated value of ITRIP due to delays in the turn
OFF of the drivers. The amount of overshoot can be
approximated as
IOUTP ≈ (VBB – [(ITRIP • RLOAD) + VBEMF]) • tpd(pwm)
LLOAD
where VBB is the load/motor supply voltage, VBEMF is the
back-EMF voltage of the load, RLOAD and LLOAD are the
resistance and inductance of the load respectively, and
tpd(pwm) is the propagation delay as specified in the electrical
characteristics table.
The reference terminal has an equivalent input resis-
tance of 50 kΩ ±30%. This should be taken into account
when determining the impedance of the external circuit
that sets the reference voltage value.
To minimize current-sensing inaccuracies caused by
ground trace IR drops, the current-sensing resistor should
have a separate return to the ground terminal of the
device. For low-value sense resistors, the IR drops in the
PCB can be significant and should be taken into account.
The use of sockets should be avoided as their contact
resistance can cause variations in the effective value of
RS.
Larger values of RS reduce the aforementioned effects
but can result in excessive heating and power loss in the
sense resistor. The selected value of RS must not cause
the SENSE terminal absolute maximum voltage rating to
be exceeded. The recommended value of RS is in the
range of
RS = (0.375 to 1.125)/ITRIP.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
This also improves the maximum rate at which the load
current can increase (as compared to fast decay) due to
the slow rate of decay during toff. When the average load
current is decreasing, fast-decay mode is used to regulate
the load current to the desired level. This prevents tailing
of the current profile caused by the back-EMF voltage of
the stepper motor.
In stepper motor applications applying a constant
current to the load, slow-decay mode PWM is used
typically to limit the switching losses in the device and iron
losses in the motor.
DC Motor Applications
In closed-loop systems, the speed of a dc motor can
be controlled by PWM of the PHASE or ENABLE inputs, or
by varying the REF input voltage (VREF). In digital systems
(microprocessor controlled), PWM of the PHASE or
ENABLE input is used typically thus avoiding the need to
generate a variable analog voltage reference. In this case,
a dc voltage on the REF input is used typically to limit the
maximum load current.
In dc servo applications that require accurate position-
ing at low or zero speed, PWM of the PHASE input is
selected typically. This simplifies the servo-control loop
because the transfer function between the duty cycle on
the PHASE input and the average voltage applied to the
PCB Layout
The load supply terminal, VBB, should be decoupled
(>47 µF electrolytic and 0.1 µF ceramic capacitors are
recommended) as close to the device as is physically
practical. To minimize the effect of system ground I•R
drops on the logic and reference input signals, the system
ground should have a low-resistance return to the load
supply voltage.
See also “Current Sensing” and “Thermal Consider-
ations” above.
Fixed Off-Time Selection
With increasing values of toff, switching losses de-
crease, low-level load-current regulation improves, EMI is
reduced, the PWM frequency will decrease, and ripple
current will increase. The value of toff can be chosen for
optimization of these parameters. For applications where
audible noise is a concern, typical values of toff are chosen
to be in the range of 15 to 35 µs.
Stepper Motor Applications
The MODE terminal can be used to optimize the
performance of the device in microstepping/sinusoidal
stepper motor drive applications. When the average load
current is increasing, slow-decay mode is used to limit the
switching losses in the device and iron losses in the motor.
Typical Bipolar Stepper Motor Application
25 kΩ
+
820 pF
0.5 Ω
V
BB
1234567891011 12
V
CC
V
BB
LOGIC
12345678910
11 12
V
CC
V
BB
LOGIC
Dwg. EP-048
MODE
2
ENABLE
2
PHASE
2
V
REF2
MODE
1
ENABLE
1
PHASE
1
V
REF1
47 µF
+5 V
0.5 Ω
25 kΩ820 pF
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Typical DC Servo Motor Application
47 µF
+
1
2
3
4
5
6
7
89
10
11
12
13
14
15
16
V
CC
V
BB
V
BB
LOGIC
Dwg. EP-047
25 kΩ
0.5 Ω
V
BB
MODE
PHASE
ENABLE
BRAKE
820 pF
+5 V
motor is more linear than in the case of ENABLE PWM
control (which produces a discontinuous current at low-
current levels).
With bidirectional dc servo motors, the PHASE termi-
nal can be used for mechanical direction control. Similar
to when braking the motor dynamically, abrupt changes in
the direction of a rotating motor produce a current gener-
ated by the back EMF. The current generated will depend
on the mode of operation. If the internal current-control
circuitry is not being used, then the maximum load current
generated can be approximated by
ILOAD = (VBEMF + VBB)/RLOAD
where VBEMF is proportional to the motor’s speed. If the
internal slow-decay current-control circuitry is used, then
the maximum load current generated can be approximated
by ILOAD = VBEMF/RLOAD. For both cases, care must be taken
to ensure the maximum ratings of the device are not
exceeded. If the internal fast-decay current-control
circuitry is used, then the load current will regulate to a
value given by
ILOAD = VREF/(10•RS).
CAUTION: In fast-decay mode, when the direction of
the motor is changed abruptly, the kinetic energy stored in
the motor and load inertia will be converted into current
that charges the VBB supply bulk capacitance (power
supply output and decoupling capacitance). Care must be
taken to ensure the capacitance is sufficient to absorb the
energy without exceeding the voltage rating of any devices
connected to the motor supply.
See also, the sections on brake operation under
“Functional Description,” above.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
A3952SB
Dimensions in Inches
(controlling dimensions)
Dimensions in Millimeters
(for reference only)
NOTES: 1. Leads 1, 8, 9, and 16 may be half leads at vendor’s option.
2. Webbed lead frame. Leads indicated are internally one piece.
3. Lead thickness is measured at seating plane or below.
4. Lead spacing tolerance is non-cumulative.
5. Exact body and lead configuration at vendor’s option within limits shown.
0.020
0.008
0.300
BSC
Dwg. MA-001-17A in
0.430
MAX
16
18
0.280
0.240
0.210
MAX
0.070
0.045
0.015
MIN
0.022
0.014
0.100
BSC
0.005
MIN
0.150
0.115
9
0.775
0.735
NOTE 4
0.508
0.204
7.62
BSC
Dwg. MA-001-17A mm
10.92
MAX
16
18
7.11
6.10
5.33
MAX
1.77
1.15
0.39
MIN
0.558
0.356
2.54
BSC 0.13
MIN
3.81
2.93
9
19.68
18.67
NOTE 4
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
NOTES: 1. Index is centered on “D” side.
2. Webbed lead frame. Leads indicated are internally one piece.
3. Lead spacing tolerance is non-cumulative.
4. Exact body and lead configuration at vendor’s option within limits shown.
5. Intended to meet new JEDEC Standard when that is approved.
A3952SEB
Dimensions in Inches
(controlling dimensions)
Dimensions in Millimeters
(for reference only)
18 12
0.020
MIN
0.050
BSC
128
INDEX AREA
Dwg. MA-005-28A in
0.026
0.032
0.013
0.021
26
25
19 11
4
5
0.165
0.180 0.495
0.485
0.456
0.450
0.495
0.485
0.456
0.450
0.219
0.191
0.219
0.191
0.51
MIN
4.57
4.20
1.27
BSC
12.57
12.32
11.582
11.430
128
INDEX AREA
Dwg. MA-005-28A mm
0.812
0.661
0.331
0.533
12.57
12.32
26
25
19
18 12
11
4
5
11.58
11.43
5.56
4.85
5.56
4.85
3952
FULL-BRIDGE
PWM MOTOR DRIVER
0° TO 8°
1 2 3
0.2992
0.2914
0.4133
0.3977
0.491
0.394
0.020
0.013
0.0926
0.1043
0.0040 MIN.
0.0125
0.0091
0.050
0.016
Dwg. MA-008-17 in
0.050
BSC
16 9
A3952SLB
Dimensions in Inches
(for reference only)
Dimensions in Millimeters
(controlling dimensions)
0° TO 8°
9
1
16
23
7.60
7.40
10.50
10.10
10.65
10.00
0.51
0.33
2.65
2.35
0.10 MIN.
0.32
0.23
1.27
0.40
Dwg. MA-008-17A mm
1.27
BSC
NOTES: 1. Webbed lead frame. Leads indicated are internally one piece.
2. Lead spacing tolerance is non-cumulative.
3. Exact body and lead configuration at vendor’s option within limits shown.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Dwg. MP-007 in
1.260
1.240
0.775
0.765
0.020 0.155
0.145 ø
0.180
MAX
0.055
0.045
0.135
0.100
0.290 MIN
0.080
0.070
0.365
0.100
±0.010
0.030
0.020
0.065
0.035 10.023
0.018
0.140
0.570
0.540
0.245
0.225
12
INDEX
AREA
A3952SW
Dimensions in Inches
(controlling dimensions)
Dimensions in Millimeters
(for reference only)
Dwg. MP-007 mm
32.00
31.49
19.69
19.45
0.51 3.94
3.68 ø
4.57
MAX
1.40
1.14
3.43
2.54
7.36
MIN
2.03
1.77
9.27
2.54
±0.254
0.76
0.51
1.65
0.89
1
0.59
0.45
3.56
14.48
13.71
6.22
5.71
12
INDEX
AREA
NOTES: 1. Lead thickness is measured at seating plane or below.
2. Lead spacing tolerance is non-cumulative.
3. Exact body and lead configuration at vendor’s option within limits shown.
4. Lead gauge plane is 0.030” (0.762 mm) below seating plane.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
Allegro MicroSystems, Inc. reserves the right to make, from time to time,
such departures from the detail specifications as may be required to permit
improvements in the design of its products.
The information included herein is believed to be accurate and reliable.
However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor
for any infringements of patents or other rights of third parties which may result
from its use.
3952
FULL-BRIDGE
PWM MOTOR DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
MOTOR DRIVERS SELECTION GUIDE
Function Output Ratings * Part Number †
INTEGRATED CIRCUITS FOR BRUSHLESS DC MOTORS
3-Phase Controller/Drivers ±2.0 A 45 V 2936 & 2936-120
Hall-Effect Latched Sensors 10 mA 24 V 3175 & 3177
2-Phase Hall-Effect Sensor/Controller 20 mA 25 V 3235
Hall-Effect Complementary-Output Sensor 20 mA 25 V 3275
2-Phase Hall-Effect Sensor/Driver 900 mA 14 V 3625
2-Phase Hall-Effect Sensor/Driver 400 mA 26 V 3626
3-Phase Power MOSFET Controller — 28 V 3933
Hall-Effect Complementary-Output Sensor/Driver 300 mA 60 V 5275
3-Phase Back-EMF Controller/Driver ±900 mA 14 V 8902–A
3-Phase Back-EMF Controller/Driver ±1.0 A 7 V 8984
INTEGRATED BRIDGE DRIVERS FOR DC AND BIPOLAR STEPPER MOTORS
PWM Current-Controlled Dual Full Bridge ±750 mA 45 V 2916
PWM Current-Controlled Dual Full Bridge ±1.5 A 45 V 2917
PWM Current-Controlled Dual Full Bridge ±1.5 A 45 V 2918
PWM Current-Controlled Dual Full Bridge ±750 mA 45 V 2919
Dual Full-Bridge Driver ±2.0 A 50 V 2998
PWM Current-Controlled Full Bridge ±2.0 A 50 V 3952
PWM Current-Controlled Full Bridge ±1.3 A 50 V 3953
PWM Current-Controlled Microstepping Full Bridge ±1.5 A 50 V 3955
PWM Current-Controlled Microstepping Full Bridge ±1.5 A 50 V 3957
DMOS Full Bridge PWM Driver ±2.0 A 50 V 3958
PWM Current-Controlled Dual Full Bridge ±800 mA 33 V 3964
PWM Current-Controlled Dual Full Bridge ±650 mA 30 V 3966
PWM Current-Controlled Dual Full Bridge ±650 mA 30 V 3968
PWM Current-Controlled Dual Full Bridge ±750 mA 45 V 6219
OTHER INTEGRATED CIRCUIT & PMCM MOTOR DRIVERS
Unipolar Stepper-Motor Quad Driver 1.8 A 50 V 2544
Unipolar Stepper-Motor Translator/Driver 1.25 A 50 V 5804
Unipolar Stepper-Motor Quad Drivers 1 A 46 V 7024 & 7029
Unipolar Stepper-Motor Quad Drivers 3 A 46 V 7026
Unipolar Microstepper-Motor Quad Driver 1.2 A 46 V 7042
Unipolar Microstepper-Motor Quad Driver 3 A 46 V 7044
Voice-Coil Motor Driver ±500 mA 6 V 8932–A
Voice-Coil Motor Driver ±800 mA 16 V 8958
Voice-Coil (and Spindle) Motor Driver ±350 mA 7 V 8984
* Current is maximum specified test condition, voltage is maximum rating. See specification for sustaining voltage limits
or over-current protection voltage limits. Negative current is defined as coming out of (sourcing) the output.
† Complete part number includes additional characters to indicate operating temperature range and package style.
