NJM3771
s
APPLICATIONS INFORMATION
Current control
The output current to the motor winding is mainly determined by the voltage at the reference input and the value of
the sensing resistor, R
S
.
Chopping frequency, winding inductance, and supply voltage will affect the current level, but to much less extent.
Fast current decay setting will produce somewhat lower (average) current than slow current decay. The peak
current through the sensing resistor (and motor winding) can be expressed as:
I
M,peak
= 0.18 • (V
R
/ R
S
) [A]
i.e., with a recommended value of 1 ohm for the sensing resistor, R
S
, a 2.5 V reference voltage will produce an
output current of approximately 450 mA. To improve noise immunity on the V
R
input, the control range may be
increased to
5 volts if R
S
is correspondingly changed to 2 ohms.
V
CC
(+5 V)
+
0.1
µF
0.1
µF
V
MM
10
µF
11
V
7
8
9
Phase
1
CD
1
V
R1
Phase
2
CD
2
V
R2
RC GND
12
+5 V
15 kΩ
3 300 pF
CC
3
V
MM1
20
V
MM2
M
A1
4
M
B1
1
19
NJM 3771
M
A2
16
15
14
M
B2
C
1
10
1 kΩ
22
E
1
2
C
2
13
1 kΩ
E
2
21
5, 6,
17, 18
STEPPER
MOTOR
820 pF
1.0
Ω
RS
820 pF
1.0
Ω
RS
Pin numbers refer
to DIP package.
GND (V
MM
)
GND
(V
CC
)
Figure 6. Typical stepper motor application with NJM3771
V
CC
(+5 V)
+
0.1
µF
0.1
µF
10
µF
V
MM
5
14
D0
V DD
Sign1
CD1
7
To
P
15
16
6
17
22
1
D7
V
3
4
2
7
8
9
Phase
1
CD
1
V
R1
Phase
2
CD
2
V
R2
RC GND
12
+5 V
15 kΩ
3 300 pF
11
CC
3
V
MM1
20
V
MM2
M
A1
4
NJU 39610
A0
A1
WR
CS
RESET
V Ref
DA1
Sign2
CD2
M
B1
1
19
NJM 3771
M
A2
20
19
21
16
15
14
+2.5V
V SS
18
DA2
M
B2
C
1
10
1 kΩ
22
E
1
2
C
2
13
1 kΩ
E
2
21
5, 6,
17, 18
STEPPER
MOTOR
820 pF
1.0
Ω
RS
820 pF
1.0
Ω
RS
Pin numbers refer
to DIP package.
GND (V
MM
)
GND
(V
CC
)
Figure 7. Microstepping system with NJU39610 and NJM3771
NJRC [ NEW JAPAN RADIO ]
