A3906 データシートの表示（PDF） - Allegro MicroSystems
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A3906 Datasheet PDF : 10 Pages
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A3906
Low Voltage Stepper and Single/Dual DC Motor Driver
becomes an ideal location for a star ground point. A low imped-
ance ground will prevent ground bounce during high current
operation and ensure that the supply voltage remains stable at
the input terminal. The recommended PCB layout shown in the
diagram below, illustrates how to create a star ground under the
device, to serve both as low impedance ground point and thermal
path.
The two input capacitors should be placed in parallel, and as
close to the device supply pins as possible. The ceramic capaci-
tor should be closer to the pins than the bulk capacitor. This is
necessary because the ceramic capacitor will be responsible for
delivering the high frequency current components.
Sense Pins The sense resistors, RSx, should have a very low
impedance path to ground, because they must carry a large cur-
rent while supporting very accurate voltage measurements by
the current sense comparators. Long ground traces will cause
additional voltage drops, adversely affecting the ability of the
comparators to accurately measure the current in the windings.
As shown in the layout below, the SENSEx pins have very short
traces to the RSx resistors and very thick, low impedance traces
directly to the star ground underneath the device. If possible,
there should be no other components on the sense circuits.
Note: When selecting a value for the sense resistors, be sure not to
exceed the maximum voltage on the SENSEx pins of ±500 mV.
C2
C3
C1
U1
GND
GND
R4
R3
PCB Layout
R1
OUT1A
OUT1B
VBB
R2
OUT2B
OUT2A
+5V
C2
C3
C1
OUT1A
SENSE1
CP2 A3906
R1
GND
OUT1B
SLEEP PAD
VBB
IN1
OUT2B
IN2
SENSE2
R2
OUT1B
VBB
OUT2B
OUT2A +5V
R4
R3
A3906
PCB
Thermal Vias
Solder
Trace (2 oz.)
Signal (1 oz.)
Ground (1 oz.)
Thermal (2 oz.)
Allegro MicroSystems, Inc.
9
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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