AS2533 datasheet(5/25 Pages) AMSCO

5 / 25 page

Rev. 7

July 1998

Data Sheet

AS2533...6

Power On Reset

The on chip power on reset circuit monitors the supply

voltage (V

DD)

during off-hook. When V

DD rises above

approx. 1.2V, a power on reset occurs which clears the

RAM.

DC Conditions

The normal operating range is from 13 mA to 100 mA.

Operating range with reduced performance is from 5 mA

to 13 mA (parallel operation). In the operating range all

functions are operational.

At line currents below 13 mA the AS253x provides an

additional slope below 4.5V in order to allow parallel

operation (see figure 13).

The dc characteristic (excluding diode bridge) is

determined by the voltage at LI and the resistor R1 at line

currents above 13 mA as follows:

VLS

= VLI + ILINE ⋅ R1

The voltage at LI is 4.5V in the normal operating range.

During pulse dialling the speech circuit and other part of

the device not operating is in a power down mode to

save current. The CS pin is pulled to V

SS in order to turn

the external shunt transistor on to keep a low voltage

drop at the LS pin during make periods.

AC Impedance

The ac impedance of the circuit is set by external

components. The impedance can be real or complex.

The ac impedance is determined as follows:

ZAC

= 33 • Z1

The dc value of Z1 should be 30

Ω to maintain correct dc

performance.

Return loss and side tone cancellation can be determined

independant of each other.

Speech Circuit

The speech circuit consists of a transmit and a receive

path with dual soft clipping, mute, line loss compensation

and sidetone cancellation.

Transmit

The gain of the transmit path is 37 dB for 600

Ω line

termination from M1/M2 to LS (see test circuit figure 10).

Keyboard Connections Continued

(Either VOL or +/– keys)

Figure 2c (AS2535)

P //M

R 1

R 2

R 3

L N

N R

V O

O L

–

M 1

M 2

M 3

M 4

M 5

M 6

M 7

M 8

M 9

M 1

1 0

M 1

1 1

M 1

1 2

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