Revision 1.12, Preliminary

Page 1 of 19

austria

micro

systems

Key Features

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

Unique EMC performance

Operating range from 15mA to 100mA (down to 5mA
with reduced performance)

Few external components

General Description

AS2523/24 is a CMOS integrated circuit that incorporates
DC and AC line adaptation (DC-mask and synthesized AC-
impedance of 1000

) as well as a speech circuit with

softclipping, line loss compensation and Rx-volume control
for handset and handsfree operation. It shall act as an a/b-
line powered device, which is controlled by a CPU via a
serial interface on AS2523 or a standard dialler via a
parallel interface on AS2524 and AS2524B.

Applications

Enhanced handsfree feature phones with CallerID and
extended displays. The AS2524 and AS2524B are
developed to interface with common Taiwanese dialers.

Package

Available in 28-pin SOIC or die

Block Diagram

Telephone Line Interface and

Speakerphone Circuit

AS2523, AS2524, AS2524B

PRELIMINARY DATA SHEET

Data Sheet AS2523, AS2524, AS2524B

austria

micro

systems

Revision 1.12, Preliminary

Page 2 of 19

Pin description

Pin #

Symbol

Function

ine Current

ense Input

Analog input for sensing the line current

ine

nput

Analog input used for power extraction and line current sensing

eceive

nput

Analog input for ac-separated receive signal

STB

ide

one

alance Input

Analog input for side tone cancellation network

urrent

hunt Control Output

N-channel open drain output to control the external high power shunt transistor for
synthesizing AC- and DC-impedance, modulation of line voltage and shorting the line during
make periods of pulse dialing

omplex

mpedance Input

Analog input pin for the capacitor to program a complex impedance

upply

ource Control Output

N-channel open drain output to control the external high power source transistor for supplying
(Vpp) the loudspeaker amplifier in off-hook loudspeaking/handsfree mode

VSS

oltage

ource

Negative Analog Power Supply

VDD

oltage

rain

Positive Analog Power Supply

AGND

nalog

round

Special ground for the internal amplifiers

icrophone Input

Differential input for the handset microphone (electret)

icrophone Input

Differential input for the handset microphone (electret)

icrophone Input

Differential input for the handsfree microphone (electret)

icrophone Input

Differential input for the handsfree microphone (electret)

eceive

utput to

andset

Output for driving a dynamic earpiece with an impedance from 150

to 300

Data Sheet AS2523, AS2524, AS2524B

austria

micro

systems

Revision 1.12, Preliminary

Page 3 of 19

Pin #

Symbol

Function

xCS

hip

elect on AS2523

Chip select input of the serial interface. Internal pull-up resistor ( 100kOhm )

/xMUTE

Mute transmit-, receive- path and activate tone path on AS2524 and AS2524B

ata

nput on AS2523

Data input of the serial interface. Internal pull-up resistor ( 100kOhm )

/xPD

Power down mode for AS2524 and AS2524B (On-hook)

CLK

on AS2523

Clock input of the serial interface. Internal pull-up resistor ( 100kOhm )

/HFE

Handsfree mode operation on AS2524 and AS2524B

oudspeaker

utput. Output pin is for a 25

loudspeaker

FT1

Analog input pin for connecting a capacitor for offset cancellation.

TXO

Analog output of the transmit signal

TXV

Analog input for the transmit signal in the voice switching path

CBN

Analog input pin for connecting a capacitor for background noise monitoring.

RECI

Analog input for the handsfree receive path. Should be connected to RO via coupling
capacitor.

RECV

Analog input for receive voice switching path.

VSSA

Power supply pin for LO output amplifier.

VPP

Power supply pin for LO output amplifier.

TONEIN Analog input for DTMF-signals.

Data Sheet AS2523, AS2524, AS2524B

austria

micro

systems

Revision 1.12, Preliminary

Page 5 of 19

Functional Description

DC conditions

The normal operating mode is from 15mA to 100mA. An
operating mode with reduced performance is from 5mA to
15mA. In the line hold range from 0mA to 5mA the device
is in a power down mode.

The DC characteristic is determined by the voltage at LI-
pin and a 30

resistor between LI- and LS-pin. It can be

calculated by the following equation: V

= V

+ I

Line

. V

can be programmed to be 3.5V or 4.5V.

2/4 wire conversion

AS2523/24 has built in two Wheatstone bridges with one
common ground. This provides a maximum of
independence of AC-impedance and side tone from each
other. One can adapt side tone without changing the AC-
impedance.

AC-impedance

The AC-impedance of AS2523/24 is set to t.m. 1000

With the external capacitor at CI-pin it can be programmed
complex. With an external resistor of approx. 1.5k

connected to the LS-pin it can be programmed to 600

Side Tone

A good side tone cancellation can be achieved by using the
following equation:
Z

BAL

LINE

= 10

Transmit path

The gain of the M1/M2

LS is set to +37dB. This gain

can be changed by programming on AS2523 from +30dB to
+45dB in 1dB steps (Register Txgain), on AS2524 / 24B it
is set to +37dB per default. The input is differential with an
impedance of 10k

. The soft clip circuit limits the output

voltage at LS to 2V

There is LLC for this path.

The gain of the M3/M4

LS is set to +46dB.

This gain can be changed by programming from +39dB to
+54dB in 1dB steps on AS2523. The input is differential
with an impedance of 10k

. The soft clip circuit limits the

output voltage at LS to 2V

. There is no LLC for this path.

Receive path

The gain of the LS

RO receive path is set to +7.5dB.

This gain can be changed by programming from �7.5dB to
+7.5dB in 1dB steps (Register Rxgain). The receive input
is the differential signal of RI and STB. The soft clip circuit
limits the output voltage at RO to 1V

It prevents harsh

distortion and acoustic shock. There is LLC for this path.

The gain of the LS

LO receive path is set to +32dB.

This gain can be changed by programming from +19dB to -
34dB in 1dB steps. The user can also change the gain via
Register Handsfree receive end gain (See section
"Handsfree"). The receive input is the differential signal of
RI and STB. The soft clip circuit limits the output voltage at
LO to 1.1V

It prevents harsh distortion and acoustic

shock. There is optional LLC for this path.

Line Loss Compensation (AS2523, AS2524B)

programmable on AS2523

not activated at AS2524

permanently activated at AS2524B

When it is activated, the transmit and receive gains for
both I/O's are decreased by 6dB at line currents from
20mA to 50mA or from 45mA to 75mA.

Handsfree

The handsfree function allows voice communication without
using the handset (full 2-way speaker phone). Two voice
controlled attenuators prevent acoustic coupling between
the loudspeaker and the microphone. The voice switching
circuit has three states, namely idle, transmit or receive. In
receive mode the attenuation of the receive path and the
transmit path can be controlled by Register Handsfree
receive end gain between 0dB and -20dB. The following
table shows how voice switching is controlled

TX_atten

Backgnd

noise

monitor

Voice

switching

speech

voice switching circuit

Электронный компонент: AS2524B