A2918 Allegro MicroSystems, A2918 Datasheet - Page 4

• Manufacturer Part Number: A2918
• Description: DUAL FULL-BRIDGE PWM MOTOR DRIVER
• Manufacturer: Allegro MicroSystems

2918
DUAL FULL-BRIDGE
PWM MOTOR DRIVER
V
I
OUT
PHASE
0
+
–
t
d
t
I
off
TRIP
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
Dwg. WM-003-1A
designed to drive both windings of a bipolar stepper
motor. Output current is sensed and controlled
independently in each bridge by an external sense
resistor (R
monostable multivibrator.
in the motor winding and it is sensed by R
sense voltage (V
comparator’s input:
turns OFF the source driver of the bridge. The actual
load current peak will be slightly higher than the trip
point (especially for low-inductance loads) because of
internal logic and switching delays. This delay (t
2 µs typically. After turn-off, the motor current decays,
circulating through the ground clamp diode and sink
transistor. The source driver’s OFF time t
therefore the magnitude of the current decrease, is
determined by the monostable’s external RC timing
components, where t
kΩ to 100 kΩ and 200 pF to 500 pF.
current (the sense voltage) again is allowed to rise to
the comparator’s threshold. This cycle repeats itself,
maintaining the average motor winding current at the
desired level.
runaway current control when t
This circuitry prevents the source driver from being
re-enabled until the load current has decayed to
below the I
in high turn-ON current peaks. This peak, appearing
across R
in possible erroneous current control or high-frequency
oscillations. An external R
used to delay the action of the comparator, and thus
ignore turn-on spikes.
The A2918SWH/V dual bridges are
When the bridge is turned ON, current increases
The comparator then triggers the monostable which
When the source driver is re-enabled, the winding
Special circuitry has been included to prevent
Loads with high distributed capacitances may result
S
, will attempt to trip the comparator, resulting
S
TRIP
), an internal comparator, and an internal
level.
SENSE
I
TRIP
off
) reaches the level set at the
= R
= V
C
T
REF
C
C
C
T
/10 R
off
within the range of 20
low-pass filter may be
is set too short.
S
off
S
until the
, and
d
) is