Preliminary
AS2520/21/20B/21B
Application Diagramme
La
30
W
2k2
10 V
Lb
27
220 µ
LI
2
CI
1k2
25
26
BC327
CS
15 n
19
22
M1
M2
Vss
1
15 n
LS
RI
28
1k2
300
W
1 µ
10 µ
6
STB
4
9
VDD
VDD
1k8
7k5
Side tone
balance
network
10 n
TI
INPUT FOR DTMF
AND
TONE RINGER MELODIES
10 µ
33 n
3
RO
18
16
15
17
HS
PD
100 n
100 n
8
LSI
RTH
M3
CONTROL INPUTS
(FROM µC)
MT
LE
10
1k8
1µ5
1µ5
21
20
100 n
5
510
W
510
W
AGND
100 n
100 µ
M4
LO
1k8
24
11
100 µ
BC327
SS
33 n
MPSA92
5k6
13
10 k
32
W
VDD
High
2N5551
CM
AGND
7
Low
Off
LLC
VOL
2.2 mH
5V1
12
14
10 k
VPP
100 k
23
470 µ
AS2521
AS2520
VOL+
VOL-
VSSP
Figure 9: Application Diagramme
Applications Hints
Interface to Microcontroller
In off-hook condition the microcontroller can be supplied from VDD of AS252x. The digital inputs (HS, LE, PD, and
MT) must be kept low until VDD has reached its minimum operating voltage (>2.5V).
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.
Rev. 5.1
Page 13
May 1999
AMSCO [ AMS(艾迈斯) ]
