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A3964SB Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer A3964SB
Beschreibung DUAL FULL-BRIDGE PWM MOTOR DRIVER
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 10 Seiten
A3964SB Datasheet, Funktion
3964
DUAL FULL-BRIDGE
PWM MOTOR DRIVER
3964
DUAL FULL-BRIDGE PWM MOTOR DRIVER
A3964SLB
OUT 1B 1
SENSE 1 2
OUT 1A 3
LOAD 4
SUPPLY
GROUND 5
1
VBB
GROUND 6
VREF(IN) 7
RC 1 89
PHASE 1 9 θ1
ENABLE 1 10
20 OUT 2B
2 19 SENSE 2
18 OUT 2A
V CC
17
LOGIC
SUPPLY
16 GROUND
15 GROUND
14 V REF(OUT)
13 RC 2
θ 2 12 PHASE 2
11 ENABLE 2
Dwg. PP-047-1
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage, VBB . . . . . . . . . 33 V
Output Current, IOUT (10 µs) . . . . . . ±1.0 A*
(continuous) . . . . . . . . . . . . . ±800 mA*
Logic Supply Voltage, VCC . . . . . . . . . 7.0 V
Logic Input Voltage Range,
VIN . . . . . . . . . . . -0.3 V to VCC + 0.3 V
Sense Voltage, VS . . . . . . . . . . . . . . . 1.0 V
Reference Output Current,
IREF(OUT) . . . . . . . . . . . . . . . . . . 1.0 mA
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, and heat sinking. 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 the device’s thermal shutdown
circuitry. These conditions can be tolerated but should
be avoided.
Designed for pulse-width modulated (PWM) current control of
bipolar stepper motors, the A3964SB and A3964SLB are capable of
continuous output currents to ±800 mA and operating voltages to 30 V.
Internal fixed 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. Spe-
cial power-up sequencing is not required. Internal circuit protection
includes thermal shutdown with hysteresis, transient-suppression
diodes, and crossover-current protection.
The A3964SB is supplied in a 24-pin plastic DIP with copper heat
sink tabs; A3964SLB is supplied in a 20-lead plastic SOIC with copper
heat sink tabs. The power tabs are at ground potential and need no
electrical isolation.
FEATURES
s ±800 mA Continuous Output Current Rating
s 30 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
Always order by complete part number:
Part Number
A3964SB
A3964SLB
Package
24-Pin DIP
20-Lead Wide-Body SOIC






A3964SB Datasheet, Funktion
3964
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(IN) 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 electri-
cal 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
internal 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
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 current-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
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).
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:
(VBB – [(ITRIP • RLOAD) + VBEMF]) • tPWM
IOS
LLOAD
where VBB is the motor supply voltage, VBEMF is the back-
EMF voltage of the load, RLOAD and LLOAD are the resis-
tance 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:
0.5
RS
± 50%
ITRIPmax
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

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