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austriamicrosystems
Telephone Line Interface and
Speakerphone Circuit
AS2523, AS2524, AS2524B
Key Features
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DATA SHEET
General Description
AS2523/24 is a CMOS integrated circuit that incorporates
DC and AC line adaptation (DC-mask and synthesized AC-
C-
impedance of 1000 ) as well as a speech circuit with
softclipping, line loss compensation and Rx-volume control
e
for handset and handsfree operation. It shall act as an a/b-
ct s
a/b -
line powered device, which is controlled by a CPU via a
U
serial interface on AS2523 or a standard dialler via a
d
er
parallel interface on AS2524 and AS2524B.
4B.
B.
Block Diagram
Te
Revision 1.13
am
co s
A
nt G
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ts
til
Package
ckage
age
Available in 28 - pin SOIC or die
lable 28-pin
28-
Line/Speakerphone circuit on a 28-pin CMOS-IC, simple
inventory: same die for AS2523/24 and AS2523/24B
Serial I/F on AS2523, parallel I/F on AS2524
Enhanced voice switching
Background noise monitoring
Tx- and Rx-gain programmable on AS2523 only
Digital volume control of Rx signals on AS2523 only
DC characteristic programmable on AS2523 only
Dual softclipping in handset mode on AS2523 only
Dual softclipping in handsfree mode on AS2523 only
Loudspeaker amplifier for loudhearing and handsfree
Supply voltage generation for external circuitry
Automatic line loss compensation on AS2523 / 24B only
Real and complex impedance selectable by external
components
Side tone adaptation selectable by external components
ents
s
Unique EMC performance
Operating range from 15mA to 100mA (down to 5mA
o
with reduced performance)
Few external components
App
Applications
p
Enhanced handsfree feature phones with CallerID and
nhance
e ature
w
extende
e
an
extended displays. The AS2524 and AS2524B are
devel
develo
interf
nterf
co
com
developed to interface with common Taiwanese dialers.
lv
al
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Page 1 of 19
Data Sheet AS2523, AS2524, AS2524B
austriamicrosystems
Pin description
Pin #
15
Symbol
LS
Function
L
ine Current
S
ense Input
Analog input for sensing the line current
12
LI
L
ine
I
nput
Analog input used for power extraction and line current sensing
T
e
ch
n
i
ca
a
m
l
c s
on
A
te G
nt
st
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ll
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13
RI
R
eceive
I
nput
Analog input for ac-separated receive signal
9
STB
S
ide
T
one
B
alance Input
Analog input for side tone cancellation network
10
CS
C
urrent
S
hunt Control Output
e external
nt ransistor fo
N-channel open drain output to control the externa high power shunt transistor for
dulation lin
l
e d
synthesizing AC- and DC-impedance, modulation of line voltage and shorting the line during
make periods of pulse dialing
16
CI
C
omplex
I
mpedance Input
cito o progra
prog
mplex
ex
Analog input pin for the capacitor to program a complex impedance
14
SS
S
upply
S
ource Control Output
utput
N-channel open drain output to control the external high power source transistor for supplying
ain
c
he
p
peaker amplif
hook loudspeaking/handsfree mode
ok
(Vpp) the loudspeaker amplifi in off-hook loudspeaki
amplifier
11
VSS
V
oltage
S
ource
S
ource
ourc
V
oltage
D
rain
D
rain
A
nalog
G
round
ound
d
nalog Po
log
pply
Negative Analog Power Supply
18
VDD
owe
pply
Positive Analog Power Supply
19
AGND
Special ground for the in
internal amplifiers
und
8
M1
M
icrophone Inpu
1
crophone Input
M
icrophone Input
2
icropho
M
icrophone Input
3
M
icrophone Input
4
Differential inp for the handset microphone (electret)
ifferential input
6
M2
Diffe
Differ
Differential input for the handset microphone (electret)
7
M3
Differential input for the handsfree microphone (electret)
5
M4
Differential input for the handsfree microphone (electret)
17
RO
R
eceive
O
utput to
H
andset
Output for driving a dynamic earpiece with an impedance from 150
to 300
Revision 1.13
Page 2 of 19
Data Sheet AS2523, AS2524, AS2524B
austriamicrosystems
Pin #
25
Symbol
xCS
Function
C
hip
S
elect on AS2523
Chip select input of the serial interface. Internal pull-up resistor ( 100kOhm )
Mute transmit-, receive- path and activate tone path on AS2524 and AS2524B
/xMUTE
26
DI
D
ata
I
nput
on AS2523
Data input of the serial interface. Internal pull-up resistor ( 100kOhm )
/xPD
27
CLK
Power down mode for AS2524 and AS2524B (On-hook)
Cl
oc
k
on AS2523
Clock input of the serial interface. Internal pull-up resistor ( 100kOhm )
Handsfree mode operation on AS2524 and AS2524B
/HFE
23
2
3
4
1
20
21
24
22
28
LO
FT1
TXO
TXV
CBN
RECI
RECV
VSSA
VPP
TONEIN
L
oudspeaker
O
utput. Output pin is for a 25
Analog output of the transmit signal
loudspeaker
Analog input pin for connecting a capacitor for offset cancellation.
o o
off
Analog input for the transmit signal in the voice switching path
al
swi
p
Analog input pin for connecting a capacitor for background noise monitoring.
apacitor fo
round
m
Analog input for the handsfree rec ve pa Should be connected to RO via coupling
free receive p
e path. ould
connect
capacitor.
Analog input for receive voice s
eceive
ceive
switching path.
sw
th.
Power supply pin for LO output amplifier.
y
o
ou
mplifier.
er.
Power supply pin for LO output amplifier.
pply
ply
L
ut mplifier.
Analog input for DTMF-signals.
or
signals.
als.
Te
Revision 1.13
ch
ni
ca
am
lc s
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n A
te
G
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Page 3 of 19
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Data Sheet AS2523, AS2524, AS2524B
austriamicrosystems
Detailed Block Diagram
Te
Revision 1.13
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Page 4 of 19
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