Quad DMOS Full Bridge PWM Motor Driver

A3988

10

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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.