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A3989 Datasheet(HTML) 5 Page - Allegro MicroSystems

Part No. A3989
Description  Bipolar Stepper and High Current DC Motor Driver
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Maker  ALLEGRO [Allegro MicroSystems]
Homepage  http://www.allegromicro.com
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A3989 Datasheet(HTML) 5 Page - Allegro MicroSystems

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Bipolar Stepper and High Current DC Motor Driver
A3989
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
Device Operation The A3989 is designed to operate one
dc motor and one bipolar stepper motor. The currents in each of
the full bridges, all N-channel DMOS, are regulated with fixed
off-time pulse width modulated (PWM) control circuitry. The
peak current in each full bridge is set by the value of an external
current sense resistor, RSx, and a reference voltage, VREFx.
If the logic inputs are pulled up to VDD, it is good practice to use
a high value pullup resistor in order to limit current to the logic
inputs should an overvoltage event occur. Logic inputs include:
PHASEx, I0x, I1x, ENABLE, and MODE.
Internal PWM Current Control Each full-bridge is
controlled by a fixed off-time PWM current control circuit that
limits the load current to a user-specified value, ITRIP. Initially,
a diagonal pair of source and sink DMOS outputs are enabled
and current flows through the motor winding and RSx. When the
voltage across the current sense resistor equals the voltage on the
VREFx pin, the current sense comparator resets the PWM latch,
which turns off the source driver.
The maximum value of current limiting is set by the selection of
RS and the voltage at the VREF input with a transconductance
function approximated by:
ITripMax = VREF / (3×RS)
The stepper motor outputs will define each current step as a
percentage of the maximum current, ITripMax. The actual current at
each step ITrip is approximated by:
ITrip = (% ITripMax / 100) ITripMax
where % ITripMax is given in the Step Sequencing table.
Note: It is critical to ensure that the maximum rating of ±500 mV
on each SENSEx pin is not exceeded.
Fixed Off-Time The internal PWM current control circuitry
uses a one shot circuit to control the time the drivers remain off.
The one shot off-time, toff, is internally set to 30 µs.
Blanking This function blanks the output of the current sense
comparator when the outputs are switched by the internal current
control circuitry. The comparator output is blanked to prevent
false detections of overcurrent conditions, due to reverse recovery
currents of the clamp diodes, or to switching transients related to
the capacitance of the load. Dc motors require more blank time
than stepper motors. The stepper driver blank time, tBLANKst,
is approximately 1 μs. The dc driver blank time, tBLANKdc, is
approximately 3 μs.
Control Logic Stepper motor communication is implemented
via industry standard I1, I0, and PHASE interface. This commu-
nication logic allows for full, half, and quarter step modes. Each
bridge also has an independent VREF input so higher resolution step
modes can be programmed by dynamically changing the voltage
on the corresponding VREFx pin. The dc motor is controlled using
standard PHASE, ENABLE communication. Fast or slow current
decay during the off-time is selected via the MODE pin.
Charge Pump (CP1 and CP2) The charge pump is used to
generate a gate supply greater than the VBB in order to drive the
source-side DMOS gates. A 0.1 μF ceramic capacitor should be
connected between CP1 and CP2 for pumping purposes. A 0.1 μF
ceramic capacitor is required between VCP and VBBx to act as a
reservoir to operate the high-side DMOS devices.
Shutdown In the event of a fault (excessive junction tem-
perature, or low voltage on VCP), the outputs of the device are
disabled until the fault condition is removed. At power-up, the
undervoltage lockout (UVLO) circuit disables the drivers.
Synchronous Rectification When a PWM-off cycle is
triggered by an internal fixed off-time cycle, load current will
recirculate. The A3989 synchronous rectification feature will
turn on the appropriate MOSFETs during the current decay. This
effectively shorts the body diode with the low RDS(on) driver. This
significantly lowers power dissipation. When a zero current level
Functional Description
Functional Description


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