2-Phase Stepper Motor Bipolar Driver IC (2-Phase/1-2 Phase/W1-2 Phase Excitation)
UDN2917EB
Application Notes
qREDUCTION
AND DISPERSION OF POWER LOSS
The thermal performance can be improved by adding four ex-
ternal Schottky barrier diodes (EK13 or other) between each
output terminal and ground. In most applications, the chopping
ON time is shorter than the chopping OFF time (small ON duty).
Therefore, a great part of the power loss of the driver IC is at-
tributable to the motor regenerative current during the chopping
OFF period. The regenerative current from the motor flows
through the current sensing resistor and ground clamp diode
and returns to the motor. The voltage drop across this path
causes the power loss. On this path, the forward voltage V
F
of
ground clamp diode shows the greatest drop. This means that
adding Schottky barrier diodes will improve the thermal perfor-
mance if their V
F
characteristic is smaller than that of the inter-
nal ground clamp diode.
The external diodes also disperse the loss (a source of heat)
and reduce the package power dissipation P
D
of the driver IC.
Consequently, a greater output current can be obtained.
qCONTROL
SEQUENCE OF 1-2 OR W1-2 PHASE EXCITATION
To reduce vibration when the stepper motor is rotating, the
UDN2917EB can provide 1-2 or W1-2 phase excitation for the
control sequence without varying the V
REF
terminal voltage.
The step angle is
1/2 step : 1-2 excitation
About 1/4 step : W1-2 excitation
The control sequence is as shown below. (This sequence uses
threshold signal terminals Io and I
1
for PWM current control.)
OUT
1A
OUT
1B
OUT
2A
OUT
2B
GND
To motor
Schottky barrier
diode
Combined vector (1/4 cycle)
(4)
(3)
Phase B
(2)
(1)
(0)
Phase A
Control sequence (1-2/W1-2 phase)
(ENABLE1= ENABLE2=0)
Sequence
No.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
PH
1
0
0
0
0
X
1
1
1
1
1
1
1
X
0
0
0
Phase A
I
11
I
01
0
0
0
1
1
1
0
0
0
0
0
1
1
1
0
0
0
0
1
0
1
0
1
0
0
0
1
0
1
0
1
0
Current ratio
PH
2
X
0
0
0
0
0
0
0
X
1
1
1
1
1
1
1
Phase B
I
02
I
12
1
1
0
0
0
0
0
1
1
1
0
0
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
0
0
0
1
0
1-2 phase
Current ratio excitation
W1-2 phase
excitation
1
1
2/3
1/3
0
1/3
2/3
1
1
1
2/3
1/3
0
1/3
2/3
0
0
1/3
2/3
1
1
1
2/3
1/3
0
1/3
2/3
1
1
1
2/3
1/3
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Note: When the sequence no. is 0, 4, 8, or 12, power-down can be set as follows
I
11
=1, I
01
=0: Sequence No. 0 or 8
I
12
=1, I
02
=0: Sequence No. 4 or 12
If power-down is necessary for a sequence other than 0, 4, 8, or 12, lower the
V
REF
terminal voltage. However, do not set the voltage lower than the lower limit of the setting range.
86
UDN2917EB
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