A3964SLB Allegro Microsystems Inc, A3964SLB Datasheet - Page 7

• Manufacturer Part Number: A3964SLB
• Description: IC MOTOR DRIVER PWM DUAL 20SOIC
• Manufacturer: Allegro Microsystems Inc

Specifications of A3964SLB

• Applications: Stepper Motor Driver
• Number Of Outputs: 1
• Current - Output: ±800mA
• Voltage - Load: 5 V ~ 30 V
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -20°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A3964
The following procedure can be used to evaluate the worst case
internal PWM load current regulation in the system: set V
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
The C
t
characteristics table. When the new value of C
the value of R
R
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.
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 specifi ed
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 the
RC Blanking section, above).
Enable PWM.
the selected source and sink drivers. The corresponding pair
of fl yback 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.
source pair is enabled, producing a load current that varies with
the duty cycle and remains continuous at all times. This can have
added benefi ts 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.
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 hysteresis of the thermal shutdown circuit is
approximately 15°C.
ON(min)
T
C
T
(with the artifi cially increased value of C
T
is equal to t
then should be increased until the measured value of
T
Toggling the PHASE terminal selects which sink/
Toggling the ENABLE input turns on and off
should be decreased so the value for t
ON(min)
max as specifi ed in the electrical
An internally generated dead time
ON(min)
The PHASE and
typ) for the device.
T
T
) is equal to the
has been set,
OFF
=
Dual Full-Bridge PWM Motor Driver
REF(IN)
APPLICATION NOTES
Current Sensing.
above the calculated value of I
the drivers. The amount of overshoot can be approximated by:
where V
voltage of the load, R
inductance of the load respectively, and t
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 signifi cant 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 R
Generally, larger values of R
but can result in excessive heating and power loss in the sense
resistor. The selected value of R
maximum voltage rating of 1.0 V, for the SENSE terminal, to be
exceeded. The recommended value of R
If desired, the reference input voltage can be fi ltered by placing
a capacitor from REF
capacitor as well as R
current power-ground trace to avoid changes in REF
drops.
Thermal Considerations.
recommended that the maximum junction temperature be
kept below 110°C to 125°C. The junction temperature can be
measured best by attaching a thermocouple to the power tab/
batwing of the device and measuring the tab temperature, T
The junction temperature can then be approximated by using the
formula:
where V
for the given level of I
6°C/W.
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.
S
.
I
BB
F
OS
can be chosen from the electrical specifi cation table
is the motor supply voltage, V
≈
(V
BB
T
The actual peak load current (I
– [(I
J
≈ T
LOAD
IN
B
LOAD
R
should be independent from the high-
TRIP
to ground. The ground return for this
TAB
S
≈
For reliable operation, it is
and L
I
. The value for R
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
TRIP
x R
+ (2 I
S
reduce the aforementioned effects
0.5
TRIP
S
max
L
LOAD
LOAD
LOAD
should not cause the absolute
LOAD
due to delays in the turn off of
) + V
are the resistance and
± 50%
V
S
F
PWM
BEMF
is in the range of:
BEMF
R
θJT
θJT
is specifi ed in the
)
is the back-EMF
]) x t
is approximately
PEAK
PWM
IN
) will be
due to IR
TAB
.
6