AS2525 datasheet(9/26 Pages) AMSCO

9 / 26 page

Preliminary

AS2525

Rev. 1.3

Page 9

May 1999

Functional Description

DC Conditions

The normal operating mode is from 15 mA to 100 mA.

An operating mode with reduced performance is from

5 mA to 15 mA. In the line-hold range from 0 mA to 5

mA 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 pin LI and LS. It

can be calculated by the following equation:

LS = VLI + ILINE ∗ 30 Ω

LI can be programmed to be 3.5 V or 4.5 V.

Table 7: DC mask selection

[PG] + [0] + (Password) + [#] + [3] + (digit) + [PG]

Digit

DC Mask (dc voltage at pin LI)

[0]

Low dc mask, V

LI = 3.5 Volt

[1]

High dc mask, V

LI = 4.5 Volt

100

ILine

VLine

VLS

VLI

(V)

(mA)

Figure 7: DC characteristic with low dc mask

2/4 Wire Conversion

AS2525 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 AS2525 is set to 1000

Ω. A

complex impedance can be adjusted by connecting an

external capacitor to the CI pin. With an external

resistor of approximately 1.5 k

Ω connected to the LS

pin, it can be programmed to 600

Ω.

AC(syn) = 33 ∗ 30 Ω

Side-Tone

A good side-tone cancellation can be achieved by

using the following equation:

BAL/ZLINE = 10

This is assuming that the side-tone reference resistor,

R2 (between LI and STB) is 300

Ω and R1 is 30 Ω.

ZLINE

R1 = 30 ohm

R2 = 300 ohm

ZBAL

Figure 8: Side-tone balance

Transmit Path

The gain of the M1/M2 —> LS path is default set to

37 dB. This gain can be changed from 30 dB to 45 dB

in 1 dB steps by set-up programming.

Table 8: Handset Tx gain setting

[PG] + [0] + (Password) + [0] + [1] + (x) + [PG]

Key

(x)

Tx Gain (dB)

M1/2 to LS

Key

(x)

Tx Gain (dB)

M1/2 to LS

[0]

[8]

[1]

[9]

[2)

[M1]

[3]

[M2]

[4]

[M3]

[5]

[M4]

[6]

[M5]

[7]

[M6]

The input is differential with an impedance of 10 k

Ω.

The soft clip circuit limits the output voltage swing at

pin LS to 2 V

PEAK when activated.

Table 9: Handset Tx soft clipping selection

[PG] + [0] + (Password) + [#] + [4] + (digit) + [PG]

Digit

Handset Tx Soft Clipping

[0]

Disabled

[1]

Enabled (2 V

PEAK)

There is optional LLC for this path.

The gain of the M3/M4 —> LS path is default set to

46 dB. This gain can be changed from 39 dB to 54 dB

in 1 dB steps by set-up programming.

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