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A3989 Datasheet(PDF) 6 Page - Allegro MicroSystems

Part No. A3989
Description  Bipolar Stepper and High Current DC Motor Driver
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Manufacturer  ALLEGRO [Allegro MicroSystems]
Direct Link  http://www.allegromicro.com
Logo ALLEGRO - Allegro MicroSystems

A3989 Datasheet(HTML) 6 Page - Allegro MicroSystems

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Bipolar Stepper and High Current DC Motor Driver
A3989
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
is detected, synchronous rectification is turned off to prevent
reversal of the load current.
Mixed Decay Operation The stepper driver operates 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. The dc driver decay mode is determined by the MODE
pin. 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.
MODE Control input MODE is used to toggle between fast
decay mode and slow decay mode for the dc driver. A logic high
puts the device in slow decay mode. Synchronous rectification is
always enabled when ENABLE is low.
Braking Driving the device in slow decay mode via the MODE
pin and applying an ENABLE chop command implements
the Braking function. Because it is possible to drive current in
both directions through the DMOS switches, this configura-
tion effectively shorts the motor-generated BEMF as long as the
ENABLE chop mode is asserted. The maximum current can be
approximated by VBEMF/RL. Care should be taken to ensure that
the maximum ratings of the device are not exceeded in worst case
braking situations: high speed and high inertia loads.
VPHASE
IOUT
IOUT
+
0
See Enlargement A
Enlargement A
FDDT
SDDT
9 µs
21 µs
Fixed Off-Time 30 µs
I
Trip
FDSR
SD
SR
SDDT
Figure . Mixed Decay Mode Operation


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