NJM3774 New Japan Radio, NJM3774 Datasheet - Page 6

• Manufacturer Part Number: NJM3774
• Description: DUAL STEPPER MOTOR DRIVER
• Manufacturer: New Japan Radio

Current control
The output current to the motor is de-termined by the voltage at the reference input and value of sensing resistor,
R
output current can be switched off com-pletely by a HIGH input level at the Dis-able input (Dis1 and Dis2 for
respective channels). When Disable goes HIGH, all four transistors in the output stage are switched off, and the
output current rapidly drops to zero (“fast current decay” – see figure 3).
I
960 mA.
spondingly changed (for example to 1ohm for 900 mA max output current).
External components
For the device to function properly, four external free-wheeling diodes must be connected, as in figure 6. The
diodes should be of fast type with a reverse recovery time of less than 100 ns. Com-monly used types are UF4001
or BYV27.
recommended filter component values, 1 kohm and 820 pF, are suitable for a wide range of motors and operational
conditions.
the sensing resistor, and hence the peak motor current, will reach a slightly higher level than what is defined by the
comparator threshold, V
performance. Increasing the time constant may result in unstable switching. The time constant should be adjusted
by changing the C
M,peak
S
Chopping frequency, winding induc-tance and supply voltage also affect the current, but to much less extent. The
The peak motor current through the sensing resistor and the motor winding can be expressed as:
A 2.5 V reference voltage and a 0.47 ohm sensing resistor will produce an out-put current level of approximately
A low pass filter in series with the com-parator input prevents erroneous switch-ing due to switching transients.The
Since the low-pass filtering action in-troduces a small delay of the signal to the comparator, peak voltage across
The time constant of the low-pass fil-ter may therefore be reduced to minimize the delay and optimize low-current
.
To improve noise immunity at the V
APPLICATIONS INFORMATION
= 0.18 • ( V
R
C
/ R
Figure 6. Typical stepper motor driver application with NJM3774.
value.
S
) [A]
CH
+5 V
+5 V
GND (V
, set by the reference input V
15 k
3300 pF
19
18
20
26
27
25
CC
23
0.1 F
)
Phase
Dis
V
Phase
Dis
V
RC
R1
R2
1
2
1,
3,
13, 14,
15, 16,
17, 28.
GND
R
1
2
input, the voltage control range can be increased to 5 V if R
V
2,
9,
CC
22
NJM3774
C
1
21
820 pF
1 k
V
R S
MM1
10
11
E
1
0.68
24
C
R
V
2
(V
820 pF
MM2
5
1 k
CH
R S
= 450 mV at V
M
M
M
M
6
E
A1
B1
A2
B2
2
0.68
12
8
4
7
D3
D1
D1 - D4 are UF 4001 or
BYV 27, t
Pin numbers refer to
PLCC package.
D4
D2
R
= 2.5 V).
V
MM
rr
STEPPER
+
10 F
MOTOR
100 ns.
V
MM
NJM3774
S
is corre-