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A3988 Datasheet(PDF) 6 Page - Allegro MicroSystems

Part No. A3988
Description  Quad DMOS Full Bridge PWM Motor Driver
Download  13 Pages
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Manufacturer  ALLEGRO [Allegro MicroSystems]
Direct Link  http://www.allegromicro.com
Logo ALLEGRO - Allegro MicroSystems

A3988 Datasheet(HTML) 6 Page - Allegro MicroSystems

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Quad DMOS Full Bridge PWM Motor Driver
A3988
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Synchronous Rectification When a PWM-off cycle is
triggered by an internal fixed off-time cycle, load current will
recirculate. The A3988 synchronous rectification feature will turn
on the appropriate MOSFETs during the current decay, and effec-
tively short out the body diodes with the low RDS(on) driver. This
significantly lowers power dissipation. When a zero current level
is detected, synchronous rectification is turned off to prevent
reversal of the load current.
Mixed Decay Operation The bridges operate in mixed
decay mode. Referring to figure 2, as the trip point is reached, the
device goes into fast decay mode for 30.1% of the fixed off-time
period. After this fast decay portion, tFD, the device switches
to slow decay mode for the remainder of the off-time. During
transitions from fast decay to slow decay, the drivers are forced
off for approximately 600 ns. This feature is added to prevent
shoot-through in the bridge. As shown in figure 2, during this
“dead time” portion, synchronous rectification is not active, and
the device operates in fast decay and slow decay only.
VPHASE
IOUT
IOUT
+
0
See Enlargement A
Enlargement A
FDDT
SDDT
9 μs21 μs
Fixed Off-Time 30 μs
I
Trip
FD
SR
SD
SR
SDDT
Figure 2. Mixed Decay Mode Operation


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