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PT2256 V1.7

- 5 -

August, 2006

Electronic Volume Controller IC

PT2256

FUNCTION DESCRIPTION

ATTENUATION

The PT2256 volume control circuit consists of ladder resistors and analog switches. The Tap for

loudness function is connected to the Step 10 (-20dB). When the (3.9KΩ) resistor is connected

between LT and AGND pins, the attenuation is given in table below.

The equivalent circuit is shown below:

Step

Attenuation

(dB)

Step

Attenuation

(dB)

0

0

16

-32

1

-2

17

-34

2

-4

18

-36

3

-6

19

-38

4

-8

20

-40

5

-10

21

-42

6

-12

22

-46

7

-14

23

-50

8

-16

24

-54

9

-18

25

-58

10

-20

26

-62

11

-22

27

-66

12

-24

28

-70

13

-26

29

-74

14

-28

30

-78

15

-30

31

∞

OUT

IN

LT

AGND

Step 0

Step 1

Step 9

Step 10

Step 11

Step 31

Step 30

Step 2

Note: Step 22 has an initial value of -46dB.