TA8473F/FG/FN/FNG

2006-3-2

3

HALF−SPEED SYSTEM

To

lower

the

motor

speed,

TA8473F/FG

and

TA8473FN/FNG set the off−time during the output timings

(Fig.1). Starting the multivibrator (MMV) enables the

off−time. The off−time is set by the time constant of

capacitor Ch connected to the HS terminal and IC internal

resistor Rh. A thermistor can also be used to control

off−time depending on the temperature.

(1) Determining Ch

The MMV operation can be monitored through the HS

and HS, generating a transient with the external Ch.

The maximum peak level value is set to about 5 V and

the bottom level to about 1 V.

The off−time is determined as follows :

1

5

1

V

og

×

Ch·Rh

=

T

CC

-

-

l

For example, at Ch = 0.1 µF, Rh = 100 k

V, off−time is about 4.4 ms. Since Rh is an internal

resistor, a fluctuation of ±30% is permitted. The

temperature characteristic is 0.5% /

°C.

(2) Determining off−time

If approximately the same off−time (×1~1.3) is set for the

on timing when the motor is running at full speed, a number of rotations decreases to about half. As the

coefficient depends on the motor, determine the off−time value by experimenting.

The number of rotations can be set to any value. However, if the value is too low, the motor can be started

but not run stably.

(3) Detecting temperature and controlling rotations

TA8473F/FG and TA8473FN/FNG compare the TH terminal thermistor and the value of the resistor

altering the peak operation level of MMV. That is, TA8473F/FG and TA8473FN/FNG internally apply a

terminal determined using the thermistor resistance, and another internal reference current.

Fig. 1