A3989_V データシートの表示（PDF） - Allegro MicroSystems
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A3989_V Datasheet PDF : 13 Pages
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A3989
Bipolar Stepper and High Current DC Motor Driver
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 0
See Enlargement A
–
Enlargement A
ITrip
Fixed Off-Time 30 μs
9 μs
21 μs
IOUT
FDDT
FDSR
SDDT
SDSR
Figure 2. Mixed Decay Mode Operation
SDDT
Allegro MicroSystems, LLC
6
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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