LA1235

No.873-5/12

• Setting of muting circuit constnats

Drive current to be output at muting drive output pin 12 is 0.75mA typ., but

approximately 0.4mA may be caused by variations in characteristic or

changes in temperature (smaller at higher temperatures). It is desirable to

design the circuit so that the total current to be output from pin 12 at the time

of muting ON does not exceed 0.35mA. When driving the muting circuit of

the LA1235, the muting drive current (input current at pin 5) must be

considered besides this total output current. The muting drive current of the

LA1235 is 0.2mA max.

Thus, the muting constants are obrained as follows. If the muting drive

by the following expression.

Muting attenuation becomes as shown in Mute (att)

–

fm (next page) characteristic. This phenomenon occurs

at modulation frequency 100Hz becomes –80dB.

AF Output Circuit

+

6.2V

4.8V

(10k

Ω : Input resistance at pin 5, Refer to the above figure.)

Muting Circuit