M65856SP

Rev.1.0, Sep.22.2003, page 13 of 18

(5) ALC level diagram

-30

-20

-10

0

+3

10

- 50 - 40 - 30 - 20 - 10

Mic amplifier gain 47 dB set value

ALC operating voltage setting range

Vo(dBV)

Vi(dBV)

-60

-70

(6) ALC operating voltage setting

The ALC operating voltage may be set to any desired value within a range of -10 dBV to +3 dBV, depending on the

value of the direct current voltage applied to Pin 3 (ALC operating voltage setting).

Peak voltage Vpo of

wave height on one side

VALC: Voltage applied to Pin [3]

OV

VALC=

Vcc- Vpo

2.5V(

Vcc )

Internal direct current bias

1

2

1

2

Example showing the ALC operating voltage set to -5 dB (when Vcc = 5 V)

-5 dBV = 0.56 Vrms = 1.59 Vp-p = 0.8 Vp-o

VALC = 2.5 - 0.8 = 1.7 V

Because of the high input impedance of Pins 5 and 10, which exceeds 1 M

Ω, the ALC reference voltage can be applied

by splitting the resistance.

3

Vcc

51k

0.01

µ

R

at Vcc = 5 V:

ALC operating voltage (dBV)

Voltage VALC (V)

applied to Pins 5 and 10

Resistance R (

Ω)

+3

0.50

5.6 k

0

1.09

15 k

–2

1.38

20 k

–4

1.61

24 k

–6

1.79

27 k

–8

1.94

33 k

–10

2.05

36 k