2916
DUAL FULL-BRIDGE
MOTOR DRIVER
LOGIC CONTROL OF OUTPUT CURRENT
Two logic level inputs (l
0
and I
1
) allow digital selection of the motor
winding current at 100%, 67%, 33%, or 0% of the maximum level per
the table. The 0% output current condition turns OFF all drivers in the
bridge and can be used as an OUTPUT ENABLE function.
sequence. This is accomplished by digitally
selecting 100% drive current when only one
phase is ON and 67% drive current when two
phases are ON. Logic highs on both l
0
and l
1
turn OFF all drivers to allow rapid current
decay when switching phases. This helps to
ensure proper motor operation at high step
rates.
The logic control inputs can also be
used to select a reduced current level (and
reduced power dissipation) for ‘hold’ condi-
tions and/or increased current (and available
torque) for start-up conditions.
GENERAL
The PHASE input to each bridge
determines the direction motor winding
current flows. An internally generated
deadtime (approximately 2 µs) prevents
crossover currents that can occur when
switching the PHASE input.
All four drivers in the bridge output can
be turned OFF between steps (l
0
= l
1
ž 2.4 V)
resulting in a fast current decay through the
internal output clamp and flyback diodes. The
fast current decay is desirable in half-step and
high-speed applications. The PHASE, l
0
,and I
1
inputs float high.
Varying the reference voltage (V
REF
)
provides continuous control of the peak load
current for micro-stepping applications.
Thermal protection circuitry turns OFF
all drivers when the junction temperature
reaches +170°C. It is only intended to protect
the device from failures due to excessive
junction temperature and should not imply
that output short circuits are permitted. The
output drivers are re-enabled when the
junction temperature cools to +145°C.
The UDN2916B/EB/LB output drivers
are optimized for low output saturation
voltages—less than 1.8 V total (source plus
sink) at 500 mA. Under normal operating
conditions, when combined with the excellent
thermal properties of the batwing package
design, this allows continuous operation of
both bridges simultaneously at 500 mA.
CURRENT-CONTROL TRUTH TABLE
l
0
L
H
L
H
I
1
L
L
H
H
Output Current
V
REF
/10 R
S
= I
TRIP
V
REF
/15 R
S
= 2/3 I
TRIP
V
REF
/30 R
S
= 1/3 I
TRIP
0
These logic level inputs greatly enhance the implementation of
µP-controlled drive formats.
During half-step operations, the l
0
and l
1
allow the µP to control the
motor at a constant torque between all positions in an eight-step
TYPICAL APPLICATION
STEPPER
MOTOR
1
2
R
S
R
C
C
C
3
4
5
6
7
8
FROM
µP
9
9
2
V
BB
V
24
23
R
S
R
C
22
21
20
19
18
17
FROM
µP
C
C
+
BB
1
PWM 1
θ
1
16
15
14
V
REF
10
V
REF
θ
2
11
12
820 pF
C
T
V
CC
PWM 2
820 pF
+5 V
C
T
13
56 kΩ
R
T
56 kΩ
R
T
Dwg. EP-008B1
www.allegromicro.com
5
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