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3961 Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer 3961
Beschreibung DUAL FULL-BRIDGE PWM MOTOR DRIVER
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 10 Seiten
3961 Datasheet, Funktion
3961
DUAL FULL-BRIDGE
PWM MOTOR DRIVER
3961
DUAL FULL-BRIDGE PWM MOTOR DRIVER
Designed for pulse-width modulated (PWM) current control of
bipolar stepper motors, the A3961S— is capable of continuous output
OUT1B 1
24 OUT2B
currents to ±800 mA and operating voltages to 45 V. Internal fixed
E1 2
SENSE1 3
OUT1A 4
TVBB1 5
GROUND 6
CGROUND 7
UVREFOUT 8
D YVREFIN 9
LRC1 10
PHASE1 11
O NENABLE1 12
23 E 2
22 SENSE 2
21 OUT2A
20 V BB2
19 GROUND
18 GROUND
17 I FULL/PD
16 V CC
15 RC2
14 PHASE 2
13 ENABLE2
PR ONote the A3961SB (DIP) and the A3961SLB
(SOIC) are electrically identical and share a
Ecommon terminal number assignment.
D CABSOLUTE MAXIMUM RATINGS
E NLoad Supply Voltage, VBB . . . . . . . . . . 45 V
U EOutput Current, IOUT . . . . . . . . . . ±800 mA*
Logic Supply Voltage, VCC . . . . . . . . . 7.0 V
IN RLogic Input Voltage Range,
VIN . . . . . . . . . . . -0.3 V to VCC + 0.3 V
T ESense Voltage, VSENSE . . . . . . . . . . . . 1.0 V
N FReference Output Current,
IREF OUT . . . . . . . . . . . . . . . . . . . 1.0 mA
O EPackage Power Dissipation,
C RPD . . . . . . . . . . . . . . . . . . . . See Graph
Operating Temperature Range,
TA . . . . . . . . . . . . . . . . . -20˚C to +85˚C
IS RJunction Temperature, TJ . . . . . . . +150˚C†
Storage Temperature Range,
D FOTS . . . . . . . . . . . . . . . . -55˚C to +150˚C
off-time PWM current-control circuitry can be used to regulate the
maximum load current to a desired value. An internal precision voltage
reference is provided to improve motor peak current control accuracy.
The peak load current limit is set by the user’s selection of an external
resistor divider and current-sensing resistors.
The fixed off-time pulse duration is set by user-selected external
RC timing networks. The capacitor in the RC timing network also
determines a user-selectable blanking window that prevents false
triggering of the PWM current control circuitry during switching transi-
tions. This eliminates the need for two external RC filter networks on
the current-sensing comparator inputs.
For each bridge the PHASE input controls load current polarity by
selecting the appropriate source and sink driver pair. For each bridge
the ENABLE input, when held high, disables the output drivers. Special
power-up sequencing is not required. Internal circuit protection includes
thermal shutdown with hysteresis, transient-suppression diodes, and
crossover-current protection.
The A3961S— is supplied in a choice of two power packages:
24-pin dual-in-line plastic package with copper heat-sink tabs and
24-lead plastic SOIC with copper heat-sink tabs. In both packages the
power tab is at ground potential and needs no electrical isolation.
FEATURES
s ±800 mA Continuous Output Current Rating
s 45 V Output Voltage Rating
s Internal PWM Current Control, Saturated Sink Drivers
s Internally Generated Precision 2.5 V Reference
s Internal Transient-Suppression Diodes
s Internal Thermal-Shutdown Circuitry
s Crossover-Current Protection, UVLO Protection
* 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.
Always order by complete part number:
† Fault conditions that produce excessive
junction temperature will activate device
thermal shutdown circuitry. These conditions
can be tolerated but should be avoided.
PART NUMBER
A3961SB
A3961SLB
PACKAGE
24-Pin DIP
24-Lead SOIC
RθJA
40°C/W
55°C/W
RθJT
6°C/W
6°C/W






3961 Datasheet, Funktion
3961
DUAL FULL-BRIDGE
PWM MOTOR DRIVER
where tOFF = RTCT, RLOAD is the series resistance of the
load, VBB is the 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
dependent on the polarity and magnitude of the motor’s
back EMF.
The following procedure can be used to evaluate the
worst-case internal PWM load current regulation 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. The
CT then should be increased until the measured value of
tON(min) is equal to tON(min)max 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 = RTCT (with the artificially increased value of CT)
is equal to the nominal design value. The worst-case load-
current regulation then can be measured in the system
under operating conditions.
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 inter-
nal PWM current control is used, 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 PWM. Toggling the ENABLE input turns ON and
OFF the selected source and sink drivers. The corre-
sponding pair of flyback and ground clamp diodes conduct
after the drivers are disabled, resulting in fast current de-
cay. When the device is enabled the internal current-con-
trol circuitry will be active and can be used to limit the load
current in a slow decay mode.
Phase PWM. Toggling the PHASE terminal selects 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 be-
tween 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).
Miscellaneous Information. An internally generated dead
time prevents crossover currents that can occur when
switching phase.
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
imply that output short circuits are permitted. The hyster-
esis of the thermal shutdown circuit is approximately 15°C.
APPLICATION NOTES
Current Sensing. The actual peak load current (IPEAK)
will be above the calculated value of ITRIP due to delays in
the turn off of the drivers. The amount of overshoot can be
approximated by:
IOS
(VBB – [(ITRIP RLOAD) + VBEMF]) tPWM
LLOAD
where VBB is the 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
t PWM is specified in the electrical characteristics table.
To minimize current sensing inaccuracies caused by
ground trace IR drops, each 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.
Generally, larger values of RS reduce the aforemen-
tioned effects but can result in excessive heating and
power loss in the sense resistor. The selected value of RS
should not cause the absolute maximum voltage rating of
1.0 V, for the SENSE terminal, to be exceeded. The
recommended value of RS is in the range of:
RS
0.5
± 50%
ITRIPmax
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

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