NJM3777
s
APPLICATIONS INFORMATION
Current control
The regulated output current level to the motor winding is determined by the voltage at the reference input and the
value of the sensing resistor, R
S
. The peak current through the sensing resistor (and the motor winding) can be
expressed as:
I
M,peak
= 0.1•V
R
/ R
S
[A]
With a recommended value of 0.5 ohm for the sensing resistor R
S
, a 2.5 V reference voltage will produce an output
current of approximately 500 mA. R
S
should be selected for maximum motor current. Be sure not to exceed the
absolute maximum output current which is 900 mA. Chopping frequency, winding inductance and supply voltage
also affect the current, but to much less extent.
For accurate current regulation, the sensing resistor should be a 0.5 - 1.0 W precision resistor, i. e. less than 1%
tolerance and low temperature coefficient.
+5 V
+
V
MM
0.1
µF
13
V
10
11
8
Phase
1
Dis
1
V
R1
Phase
2
Dis
2
V
R2
RC GND
12
+5 V
12 kΩ
4 700 pF
RS
0.47
Ω
RS
0.47
Ω
CC
0.1
µF
5
V
MM1
10
µF
20
V
MM2
M
A1
4
M
B1
2
21
NJM3777E3
M
A2
15
14
17
M
B2
C
1
9
E
1
3
C
2
16
E
2
22
23
6, 7,
18, 19
STEPPER
MOTOR
Pin numbers refer
to EMP package.
GND (V
MM
)
GND (V
CC
)
Figure 6. Typical stepper motor driver application with NJM3777
V
CC
(+5 V)
+
0.1 F
0.1 F
10 F
V
MM
4
13
D0
V DD
V
Sign1
3
10
11
To
P
6 D7
14 A0
5
WR
16
CS
20
RESET
1
V Ref
DA1
2
18
8
Phase
1
Dis
1
V
R1
13
CC
5
V
MM1
20
V
MM2
M
A1
4
M
B1
2
21
NJU39612E2
Sign2
15
14
DA2
19
17
Phase
Dis
2
V
R2
RC GND
12
+5 V
12 k‰
4700 pF
2
NJM3777E3
M
A2
M
B2
C
1
9
E
1
3
C
2
16
E
2
22
23
+2.5V
VSS
17
6, 7,
18, 19
STEPPER
MOTOR
Pin numbers refer
to EMP package.
0.47 ‰
RS
0.47 ‰
RS
GND
(V
CC
)
GND (V
MM
)
Figure 7. Typical microstepping application with NJU39612
NJRC [ NEW JAPAN RADIO ]
