A2927 Ver la hoja de datos (PDF) - Allegro MicroSystems
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A2927 Datasheet PDF : 8 Pages
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2927
DUAL FULL-BRIDGE
PWM MOTOR DRIVER
APPLICATIONS INFORMATION
PWM CURRENT CONTROL:
The UDN2927EB dual bridge is designed
to drive both windings of a bipolar stepper
motor. Output current is sensed and con-
trolled independently in each bridge by an
external sense resistor (RS), internal com-
parator, and monostable multivibrator.
When the bridge is turned ON, current
increases in the motor winding and it is
sensed by the external sense resistor until
the sense voltage (VSENSE) reaches the level
set at the comparator’s input:
ITRIP = VREF/10 RS
The comparator then triggers the mon-
ostable which turns OFF the source driver of
the bridge. The actual load current peak will
be slightly higher than the trip point (espe-
cially for low-inductance loads) because of
the internal logic and switching delays. This
delay (td) is typically 2 µs. After turn-off, the
motor current will normally decay, circulating
through the external ground clamp diode and
sink transistor. The source driver’s OFF time
(and therefore the magnitude of the current
decrease) is determined by the monostable’s
external RC timing components, where toff =
RTCT within the range of 20 kΩ to 100 kΩ
and 200 pF to 500 pF.
When the source driver is re-enabled, the
winding current (the sense voltage) is again
allowed to rise to the comparator’s threshold.
This cycle repeats itself, maintaining the
average motor winding current at the desired
level.
Special circuitry has been included to
prevent runaway current control when the
fixed OFF time (toff) is set too short. This
circuitry prevents the source driver from
being re-enabled until the load current has
decayed to below the ITRIP level.
PWM OUTPUT CURRENT WAVEFORM
V PHASE
+
I OUT 0
–
I TRIP
td
toff
Dwg. WM-003-1A
LOAD CURRENT PATHS
VBB
BRIDGE ON
RS
SOURCE OFF
ALL OFF
Dwg. EP-006-14
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
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