AS2523 datasheet(5/19 Pages) AMSCO

5 / 19 page

Data Sheet AS2523, AS2524, AS2524B

austriamicrosystems

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

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

calculated by the following equation: VLS = VLI + ILine *

Ω. VLI 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

Ω.

With the external capacitor at CI-pin it can be programmed

complex. With an external resistor of approx. 1.5k

Ω

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

Ω.

Side Tone

A good side tone cancellation can be achieved by using the

following equation:

ZBAL/ZLINE = 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

Ω. The soft clip circuit limits the output

voltage at LS to 2Vp. 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

Ω. The soft clip circuit limits the

output voltage at LS to 2Vp. 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 1Vp. 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

"Handsfree"). The receive input is the differential signal of

RI and STB. The soft clip circuit limits the output voltage at

LO to 1.1Vp. 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

AS2523 Datasheet(PDF) 5 Page - ams AG

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