AS2522BQ datasheet(5/19 Pages) AMSCO

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Data Sheet AS2522B

austriamicrosystems

Revision 3.4

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

AS2522 has a built-in dual Wheatstone bridge 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 AS2522 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 from +30dB to +45dB in

1dB steps (Register Txgain). 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. 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 +1dB.

This gain can be changed by programming from -6dB to

+9dB 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

→ LO1/LO2 receive path is set to

+29dB. This gain can be changed by programming from

+22dB to -37dB in 1dB steps. The user can also change

the gain via Register VOL (See section "Handsfree"). The

receive input is the differential signal of RI and STB. The

soft clip circuit limits the output voltage at LO1 of LO2 to

1Vp. It prevents harsh distortion and acoustic shock. There

is optional LLC for this path.

Line Loss Compensation

The line loss compensation is programmable (Register

0x0C). 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 VOL between

0dB and -20dB. The following table shows how voice

switching is controlled

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