A3992 Allegro MicroSystems, Inc., A3992 Datasheet - Page 9

• Manufacturer Part Number: A3992
• Description: DMOS Dual Full-Bridge Microstepping PWM Motor Driver
• Manufacturer: Allegro MicroSystems, Inc.

A3992
Synchronous Rectifi cation.
is triggered, by a bridge disable command or internal
fi xed off-time cycle, load current recirculates accord-
ing to the decay mode selected by control logic. The
A3992 synchronous rectifi cation feature turns on the
appropriate MOSFETs during current decay, and effec-
tively shorts out the body diodes with the low R
driver. This lowers power dissipation signifi cantly, and
can eliminate the need for external Schottky diodes for
most applications.
Three distinct modes of operation can be confi gured
Current Sensing.
ing the I
drops, the sense resistor should have an independent
ground return to the GND terminal of the device. For
low value sense resistors, the I•R drops in the PCB
sense resistor traces can be signifi cant and should
be taken into account. The use of sockets should
be avoided because they can introduce variation in
R
Allegro MicroSystems recommends a value of R
given by:
SENSE
A. Minimum Data Setup Time
B. Minimum Data Hold Time
C. Minimum Setup Strobe to Clock rising edge
D. Minimum Clock High Pulse Width
E. Minimum Clock Low Pulse Width
Serial Port Timing Diagram
due to their contact resistance.
PEAK
current level caused by ground trace I•R
R
SENSE
To minimize inaccuracies in sens-
STROBE
CLOCK
SLEEP
DATA
= 0.5 / I
TRIP MAX
When a PWM off-cycle
H
C
A
MSB
.
Applications Notes
B
D
120 ns
DS(on)
SENSE
15 ns
10 ns
40 ns
40 ns
Microstepping PWM Motor Driver
F. Minimum Setup Clock rising edge to Strobe
G. Minimum Strobe Pulse Width
H. Minimum Sleep to Clock Setup Time
I. Setup “Idle” Release to Output Enable
with the two serial port control bits:
1. Active mode. Prevents reversal of load current.
2. Passive mode. Allows reversal of current, but will
3. Disabled. Prevents MOSFET switching during load
Thermal Protection
when the junction temperature reaches 165°C typical.
It is intended only to protect the device from failures
due to excessive junction temperatures, and should not
imply that output short circuits are permitted. Thermal
shutdown has a hysteresis of approximately 15°C.
Serial Port Write Timing Operation.
into a shift register on the rising edge of a CLOCK
signal. Normally, STROBE is held high, and is only
brought low to initiate a write cycle. The data is writ-
ten MSB fi rst. Refer to the diagram below for timing
requirements.
E
Turns off synchronous rectifi cation when a 0 current
level is detected.
turn off the synchronous rectifi er circuit if the load
current inversion ramps up to the current limit.
recirculation in fast decay portion of the off-time. Dur-
ing the slow decay portion of the off-time, the low-side
switch turns on, which recirculates current through the
low-side MOSFET and low-side body diode.
DMOS Dual Full-Bridge
LSB - D0
F
. Circuitry turns off all drivers
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
G
Data is clocked
120 ns
50 ns
50 μs
1 ms
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