A3959 View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
Manufacturer
A3959 Datasheet PDF : 11 Pages
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A3959
DMOS Full-Bridge PWM Motor Driver
FUNCTIONAL DESCRIPTION (continued)
Current Sensing. To minimize inaccuracies in
sensing the ITRIP current level, which may be caused by
ground trace IR drops, the sense resistor should have an
independent ground return to the ground terminal of the
device. For low-value sense resistors the IR drops in the
PCB sense resistor’s traces can be significant and should
be taken into account. The use of sockets should be
avoided as they can introduce variation in RS due to their
contact resistance.
The maximum value of RS is given as RS = 0.5/ITRIP.
Thermal Protection. Circuitry turns off all drivers
when the junction temperature reaches 165°C typically. It
is intended only to protect the device from failures due to
excessive junction temperatures and should not imply that
output short circuits are permitted. Thermal shutdown has
a hysteresis of approximately 15°C.
Layout. A star ground system located close to the driver
is recommended. The printed wiring board should use a
heavy ground plane. For optimum electrical and thermal
performance, the driver should be soldered directly onto
the board. The ground side of RS should have an indi-
vidual path to the ground terminals of the device. This path
should be as short as is possible physically and should not
have any other components connected to it. It is recom-
mended that a 0.1 μF capacitor be placed between SENSE
and ground as close to the device as possible; the load sup-
ply terminal, VBB, should be decoupled with an electrolyt-
ic capacitor (> 47 μF is recommended) placed as close to
the device as is possible. On the 28-lead TSSOP package,
the copper ground plane located under the exposed thermal
pad is typically used as a star ground.
Allegro MicroSystems, Inc.
8
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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