Datasheet A3952KEB, A3952KB, A3952SW, A3952SLB, A3952SEB Datasheet (Allegro)

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 crossover­current 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 R

θJA

R

θJT

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, V

BB

.................. 50 V

Output Current, I

OUT

(t

w

≤ 20 µs).................................. ±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 VCC + 0.3 V

Sense Voltage, V

SENSE

...................... 1.5 V

Reference Voltage, V

REF

.................... 15 V

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.

3952

MODE

GROUND

GROUND

LOGIC

SUPPLY

PHASE

GROUND

GROUND

RC

SENSE

LOAD
SUPPLY

Dwg. PP-056

BRAKE

REF

LOAD
SUPPLY

V

CC

OUT

B

OUT

A

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 [phone]

V

BB

RC

V

CC

LOGIC

SUPPLY

LOAD

SUPPLY

PHASE

EMITTERS

UVLO

& TSD

R

S

Dwg. FP-036

MODE

REF

OUT

A

OUT

B

ENABLE

SENSE

–

+

BRAKE

9R

R

INPUT LOGIC

GROUND

Q

R
S

1.5 V

PWM LATCH

V

CC

+ –

BLANKING

SLEEP &
STANDBY MODES

V

TH

'EB' ONLY

'B', 'LB', & 'W'
PACKAGES

R

T

C

T

FUNCTIONAL BLOCK DIAGRAM

TRUTH TABLE

BRAKE ENABLE PHASE MODE OUT

A

OUTBDESCRIPTION

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 V

sense

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 T

A

= +25°C, V

BB

= 50 V, VCC = 5.0 V, V

BRAKE

= 2.0 V,

V

SENSE

= 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 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 µA

V

OUT

= 0 V – <-1.0 -50 µA

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

IF = 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 I

BB(ON)

V

ENABLE

= 0.8 V – 2.9 6.0 mA

(No Load) I

BB(OFF)

V

ENABLE

= 2.0 V, V

MODE

= 0.8 V – 3.1 6.5 mA

V

BRAKE

= 0.8 V – 3.1 6.5 mA

I

BB(SLEEP)

V

ENABLE

= V

MODE

= 2.0 V – <1.0 50 µA

12345 678 9101112

GROUND

Dwg. PP-058

MODE

LOGIC

SUPPLY

PHASE

RC

SENSE

REF

LOAD

SUPPLY

OUT

B

OUT

A

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

NOCONNECTION

EMITTERS

RC

LOAD

SUPPLY

REF

V

CC

V

BB

LOGIC

BRAKE

LOGIC

SUPPLY

PHASE

ENABLE

MODE

SENSE

LOAD

SUPPLY

OUT

B

OUT

A

Continued next page …

3952

FULL-BRIDGE
PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

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)

VIN = 2.0 V – <1.0 20 µA

I

IN(0)

VIN = 0.8 V – <-2.0 -200 µA

Reference Voltage Range V

REF

Operating 0 – 15 V

Reference Input Current I

REF

V

REF

= 2.0 V 25 40 55 µA

Reference Voltage Divider Ratio – V

REF

= 15 V 9.5 10.0 10.5 –

Comparator Input Offset Voltage V

IO

V

REF

= 0 V – ±1.0 ±10 mV

PWM RC Fixed OFF Time t

off

CT = 1000 pF, RT = 20 kΩ 18 20 22 µs

PWM Minimum ON Time t

on(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 t

pd

I

OUT

= ±2.0 A, 50% EIN to 90% E

OUT

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

t

pd(pwm)

Comparator Trip to Sink OFF – 0.8 1.5 µs

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

BRAKE

= 2.0 V – 20 30 mA

(No Load) I

CC(OFF)

V

ENABLE

= 2.0 V, V

MODE

= 0.8 V – 12 18 mA

I

CC(BRAKE)

V

BRAKE

= 0.8 V – 26 40 mA

I

CC(SLEEP)

V

ENABLE

= V

MODE

= V

BRAKE

= 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 (I

TRIP

) is set by the selection of an
external current sensing resistor (RS) 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

/(10RS).

In forward or reverse mode the current-control circuitry
limits the load current. When the load current reaches
I

TRIP

, 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 fast­decay 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 capaci­tor (CT) to determine the time period (t

off

= 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

R

S

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 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

= 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 I

TRIP

. 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

I

TRIP

= V

REF

/(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 [phone]

Brake Operation - MODE Input Low

During braking, with the MODE input low, the peak

current limit defaults internally to a value approximated by

I

TRIP

= 1.5 V/RS.

In this mode, the value of RS 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

.

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, t

off

(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

t

off

= RTCT.

When the PWM latch is reset by the current compara­tor, 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 compara­tor 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 t

off

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 approxi­mately 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 t

off

. 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 current­control circuitry can regulate load current. The limitation is
the minimum duty cycle, which is a function of the user­selected value of t

off

and the maxuimum value of the

minimum ON-time pulse, t

on(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 – V

SAT(source+sink)

) • t

on(min)

max] – [1.05 (V

SAT(sink)

+ VD) • t

off

]

1.05 (t

on(min)

max + t

off

) • R

LOAD

where t

off

= RTCT, R

LOAD

is the series resistance of the

load, VBB is the load/motor supply voltage, and t

on(min)

max
is specified in the electrical characteristics table. When
the motor is rotating, the back EMF generated will influ­ence the above relationship. For brush dc motor applica­tions, 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 regula­tion in the system:

Set V

REF

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 (t

on(min)

typ) for the device. CT then

should be increased until the measured value of t

on(min)

is

equal to t

on(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
t

off

= RT•CT (with the artificially increased value of CT) is
equal to 105% of the nominal design value. The worst­case 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 t

on(min)

max of 3.8 µs. This corresponds to
a CT value of 1200 pF, which is required to ensure suffi­cient 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 charac­teristics 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 switch­ing 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 aver­age voltage applied to the motor is more linear than in the
case of ENABLE PWM control (which produces a discon­tinuous 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 gener­ate 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 C

T

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 [phone]

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 I

OUT RθJT

)

where VF is the clamp diode forward voltage and can be
determined from the electrical specification table for the
given level of I

OUT

. The value for R

θJT

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) con­nected 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 applica­tions, all four external diodes should be added for maximum
junction temperature reduction.

imply that output short circuits are permitted. The hyster­esis of the thermal shutdown circuit is approximately 15°C.

If the internal current-control circuitry is not used; the

V

REF

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 (I

OUTP

) will be greater

than the calculated value of I

TRIP

due to delays in the turn
OFF of the drivers. The amount of overshoot can be
approximated as

I

OUTP

≈

(VBB – [(I

TRIP

• R

LOAD

) + V

BEMF

]) • t

pd(pwm)

L

LOAD

where VBB is the load/motor supply voltage, V

BEMF

is the

back-EMF voltage of the load, R

LOAD

and L

LOAD

are the

resistance and inductance of the load respectively, and

t

pd(pwm)

is the propagation delay as specified in the electrical

characteristics table.

The reference terminal has an equivalent input resis­tance 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)/I

TRIP

.

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 t

off

. 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 (V

REF

). 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 position­ing 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 Consider­ations” above.

Fixed Off-Time Selection

With increasing values of t

off

, switching losses de­crease, low-level load-current regulation improves, EMI is
reduced, the PWM frequency will decrease, and ripple
current will increase. The value of t

off

can be chosen for
optimization of these parameters. For applications where
audible noise is a concern, typical values of t

off

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

1

2

3

4

5

6

78

910

11

12

V

CC

V

BB

LOGIC

1

2

3

4

5

6

78

910

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 kΩ

820 pF

3952

FULL-BRIDGE
PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

Typical DC Servo Motor Application

47 µF

+

1

2

3

4

5

6

7

8

9

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 low­current levels).

With bidirectional dc servo motors, the PHASE termi­nal 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 gener­ated 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

I

LOAD

= (V

BEMF

+ VBB)/R

LOAD

where V

BEMF

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 I

LOAD

= V

BEMF/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

I

LOAD

= V

REF

/(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

1

8

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

1

8

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 [phone]

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

2

3

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 [phone]

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

1

0.023

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 [phone]

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.