NJM3774D2 데이터 시트보기 (PDF) - Japan Radio Corporation
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NJM3774D2 Datasheet PDF : 9 Pages
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NJM3774
s APPLICATIONS INFORMATION
Current control
The output current to the motor is de-termined by the voltage at the reference input and value of sensing resistor,
RS.
Chopping frequency, winding induc-tance and supply voltage also affect the current, but to much less extent. The
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).
The peak motor current through the sensing resistor and the motor winding can be expressed as:
IM,peak = 0.18 • ( VR / RS ) [A]
A 2.5 V reference voltage and a 0.47 ohm sensing resistor will produce an out-put current level of approximately
960 mA.
To improve noise immunity at the VR input, the voltage control range can be increased to 5 V if RS is corre-
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.
A low pass filter in series with the com-parator input prevents erroneous switch-ing due to switching transients.The
recommended filter component values, 1 kohm and 820 pF, are suitable for a wide range of motors and operational
conditions.
Since the low-pass filtering action in-troduces a small delay of the signal to the comparator, peak voltage across
the sensing resistor, and hence the peak motor current, will reach a slightly higher level than what is defined by the
comparator threshold, VCH , set by the reference input VR (VCH = 450 mV at VR= 2.5 V).
The time constant of the low-pass fil-ter may therefore be reduced to minimize the delay and optimize low-current
performance. Increasing the time constant may result in unstable switching. The time constant should be adjusted
by changing the C value.
C
+5 V
V MM
+
0.1 µF
22
11
5
D1
D2
10 µF
19
V CC
Phase1
V MM1
V MM2 MA1 12
18 Dis1
20 VR1
26 Phase 2
27 Dis2
25 V R2
RC GND
NJM3774
C1
E1 C2
MB1 8
4
MA2
MB2 7
E2
23 1, 2, 21 10 24
6
+5 V 15 kΩ
3, 9,
1 kΩ
1 kΩ
13, 14,
3300 pF
15, 16,
17, 28.
820 pF
RS
820 pF
RS
GND (VCC )
0.68 Ω
0.68 Ω
STEPPER
MOTOR
D3
D4 V MM
D1 - D4 are UF 4001 or
BYV 27, trr ≤ 100 ns.
Pin numbers refer to
PLCC package.
Figure 6. Typical stepper motor driver application with NJM3774.
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