A3977(2013) 查看數據表（PDF） - Allegro MicroSystems
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A3977 Datasheet PDF : 19 Pages
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A3977
Microstepping DMOS Driver with Translator
Applications Information
Layout.
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 load supply terminal, VBB, should be decoupled
with an electrolytic capacitor (>47 μF is recommended)
placed as close to the device as possible.
To avoid problems due to capacitive coupling of the
high dv/dt switching transients, route the bridge-output
traces away from the sensitive logic-input traces. Always
drive the logic inputs with a low source impedance to in-
crease noise immunity.
Grounding. A star ground system located close to the
driver is recommended.
The 44-lead PLCC has the analog ground and the
power ground internally bonded to the power tabs of the
package (leads 44, 1, 2, 11 – 13, 22 – 24, and 33 – 35).
On the 28-lead TSSOP package, the analog ground
(lead 7) and the power ground (lead 21) must be con-
nected together externally. The copper ground plane located
under the exposed thermal pad is typically used as the star
ground.
Current Sensing. To minimize inaccuracies caused by
ground-trace IR drops in sensing the output current level,
the current-sense resistor (RS) should have an independent
ground return to the star ground of the device. This path
should be as short as possible. For low-value sense resis-
tors the IR drops in the printed wiring board 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.
Allegro MicroSystems recommends a value of RS
given by
RS = 0.5/ITRIPmax
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.
Allegro MicroSystems, LLC
10
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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