AS2540T datasheet(6/19 Pages) AMSCO

6 / 19 page

Data Sheet AS2540

austriamicrosystems

Revision 3.1

Page 5 of 18

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. The t.m. voltage at the LI pin is 4.5V. The calculation

leads to the following DC resistances: 330

Ω to 75Ω at line

currents from 15mA to 100mA.

2/4 wire conversion

AS2540 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.

A1=3.4/3.5

A2=-0.4

AC impedance

The ac impedance of AS2540 is set to t.m. 1000

Ω. With

the external capacitor at CI pin it can be programmed

complex. With a parallel impedance at the LS pin it can be

programmed to 600

Ω.

Side Tone

A good sidetone cancellation can be achieved by using the

following equation:

ZBAL/ZLINE = 10

Transmit path

The gain of the M1/M2 —> LS transmit path is set to 38dB

for ac-impedance 1000

Ω. The input is differential with an

impedance of 25k

Ω. The soft clip circuit limits the output

voltage at LS to 2Vp. The attack time is 30µs/6dB and the

decay time is 20ms/6dB.

The gain of the TIT —> LS transmit path is set to 8dB for

ac-impedance 1000

Ω. The input is single ended with an

impedance of 25k

Ω. The soft clip circuit is not active for

this input. The dynamic range of this path is 2.5Vp at LS.

Receive path

The gain of the LS —> ROH receive path is set to 2dB for

ac-impedance 1000

Ω. The receive input is the differential

signal of RI and STB. During DTMF dialling a MF comfort

tone is applied to ROH which is -30dB relative to the line

level. The soft clip circuit limits the output voltage at ROH

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

The gain of the LS —> ROT receive path is set to 0dB for

ac-impedance 1000

Ω. The receive input is the differential

signal of RI and STB. The soft clip circuit is not active for

this output.

Modescan

The DTMF-level on the line and the function of the line loss

compensation can be selected with the connection of the

MODE-pin to the keyboard matrix. The MODE-pin is

scanned once after each OFF-Hook transition.

MODE

LLC

Dtmf Level

45mA-75mA

-6dBm

45mA-75mA

-8dBm

45mA-75mA

-10dBm

20mA-50mA

-6dBm

20mA-50mA

-8dBm

20mA-50mA

-10dBm

No LLC

-6dBm

No LLC

-8dBm

No LLC

-10dBm

X indicates connection to pin mode

AS2540T Arkusz danych(PDF) 6 Page - ams AG

AS2540T Arkusz danych(HTML) 6 Page - ams AG

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Arkusz danych Pobierz

Link URL