Preliminary

AS2520/21/20B/21B

Rev. 5.1

Page 13

May 1999

Application Diagramme

TI

LI

La

Lb

Vss

CS

PD

MT

RO

M1

CI

STB

LSI

LS

RI

HS

LO

CM

LE

M3

SS

RTH

M2

M4

LLC

15 n

10 n

300

Ω

1k8

7k5

10 µ

100 n

100 n

100 µ

32

Ω

470 µ

5k6

10 k

2N5551

2.2 mH

5V1

MPSA92

33 n

510

Ω

1µ5

510

Ω

1µ5

BC327

100 µ

33 n

10 µ

BC327

10 V

30

Ω

27

25

26

1

28

4

9

16

18

15

17

10

5

24

11

12

14

7

13

20

8

3

6

22

2

19

21

VOL

100 k

23

Side tone

balance

network

15 n

100 n

100 n

2k2

1k2

1k2

220 µ

1 µ

INPUT FOR DTMF

AND

TONE RINGER MELODIES

CONTROL INPUTS

(FROM µC)

VOL+

VOL-

10 k

AS2521

AS2520

High

Low

Off

1k8

1k8

Figure 9: Application Diagramme

Applications Hints

Interface to Microcontroller

In off-hook condition the microcontroller can be supplied from V

MT) must be kept low until V

Radio Frequency Interference

The RFI sensitivity has been minimised by the consequent use of CMOS technology and one overall ground and

by having differential inputs with a relative low input impedance.

For further application information see application notes for the AS2520 series.