M51971L Datasheet, PDF (6/13 Pages) Mitsubishi Electric Semiconductor – MOTOR SPEED CONTROL

Output voltage range at pin 9 – Supply
voltage characteristics
4
3
2
Ta = -20°C
Ta = 25°C
1
Ta = 75°C
0
4
8
12
16
Supply voltage VCC (V)
MITSUBISHI <CONTROL / DRIVER IC>
M51971L/FP
MOTOR SPEED CONTROL
Buffer amplifier offset voltage –
Voltage characteristics at pin 8
160
VCC=9V
120
80
40
0
–40
0
1
2
3
4
Voltage at pin 8 V 8 (V)
Application Characteristics Example
100
90
10
0%
Upper side : Motor speed (FV conversion waveform of tacho-
generator frequency)
Lower side : Supply voltage
Horizontal axis : 20 ms/div
Time constant of motor ≈ 100 ms
How to determine Rτ and Cτ
These constants determine the motor rotating speed. If the motor
rotating speed and the number of poles of tacho-generator are
assumed to be N and P, respectively, the following relational
expression is generally established. According to the required
rotating speed, select the constant in such a way that Rτ can be
put in the range of 10kΩ – 500kΩ. When using a high resistance,
take care for leak current that may flow on the surface of the
printed circuit board.
NP
≈
1
1.20 • Rτ • Cτ
Tacho-generator output frequency –
Connection resistance characteristics at pin ¹
10000
7000
5000
3000
2000
1000
700
500
300
200
C_{τ =}
0.1_µ^{0F.0470µ.F0220µ.F01µF}
4700pF
10 20 30 50 70 100 200 300 500 1000
Connection resistance Rτ (kΩ) at pin 1 Rτ (kΩ)