Preliminary

AS2520/21/20B/21B

Rev. 5.1

Page 2

May 1999

Pin Description

Pin #

Name

Type

Description

1

LS

AI

Line Current Sense Input

This input is used for sensing the line current.

2

CI

AI

Complex Impedance Input

Input pin for the capacitor in the complex impedance.

3

RO

AO

Receive Output

This is the output for driving a dynamic earpiece with an impedance of 140

to 300 ohm.

4

V

DD

Supply

Positive Voltage Supply

This is the supply pin for the circuit.

5

A

GND

Supply

Analogue Ground

This pin is the analogue ground for the amplifiers.

6

STB

AI

Side Tone Balance Input

This is the input for the side tone cancellation network.

7

LLC

DI

Line Loss Compensation Selection Pin

LLC = V

High range

-6 dB from 45 mA to 75 mA;

LLC = A

Low range

-6 dB from 20 mA to 50 mA;

LLC = V

No regulation

gain independent of line current;

8

LSI

AO

Loudspeaker Amplifier Input

This is the input for applying the receive signal to the loudspeaker

amplifier.

9

TI

AI

DI

Tone Input

This switchable input is intended for transmitting DTMF or other signals

like messages on TAMs (Telephone Answering Machines) onto the line in

off-hook conditions and when in ringing mode to apply a PDM signal to the

loudspeaker (see also table 1).

10

RTH

AI

Receive Threshold Input

The sensibility of the receive peak detector can be adjusted by applying

the signal from RO to the RTH input through a voltage divider.

11

CM

AO

Converter Make Output

This is an output for controlling the external switching converter. It

converts the ring signal into a 4V supply voltage and is activated when PD

= high and HS, LE, MT = low.

12

V

PP

Supply

Loudspeaker Power Supply

High power supply for the output driver stage.

13

LO

AO

Output for Loudspeaker

Output pin for an ac coupled 32

Ω (25 to 50 Ω)loudspeaker.

14

V

SSP

Supply

Negative High Power Supply

This pin is the negative high power supply for the loudspeaker amplifier.

15

MT

DI

Mute Input

Dialling mute input (see also table 1).

MT = V

MT = V

16

PD

DI

Power Down Input

Input for powering down the speech circuit and loudhearing/handsfree

(see table 1).

17

LE

DI

Loudhearing Enable Input

Input for enabling loudhearing/handsfree, active high (see table 1).

18

HS

DI

Handset Switch Input

This is an input that is pulled high by the hook switch (handset) or µC

when off-hook (see table 1).