as2504 austriamicrosystems, as2504 Datasheet - Page 4

• Manufacturer Part Number: as2504
• Description: Cordless Telephone, Answering Machine Line Interface
• Manufacturer: austriamicrosystems

Preliminary Data Sheet
Functional Description
Modes of operation
There are 3 possible modes:
Idle Mode: AS2504 is disconnected from the
a/b-line (= no line current) and VDD is not
supplied by auxiliary power. All internal circuits
are powered down. Input of digital control
signals is not possible.
Line Power Mode: AS2504 is connected to the
a/b-line and VDD is generated by the internal
power
powered up. The line interface circuit is
functional (DC-mask and AC-impedance are
synthesised). Input of digital control signals is
possible.
Aux. Power Mode: AS2504 is disconnected
from the a/b-line (= no line current) and VDD is
supplied by auxiliary power. The speech circuit
is powered up. The line interface circuit is not
functional
Input of digital control signals is possible.
Start-up in Line Power Mode
As soon as AS2504 is supplied with line
current, the external V
charged up via the LI- and VDD-pin. After the
V
2V, the line interface circuit and the selected
signal path of the speech circuit is switched on.
This off-hook status is signalled to the internal
logic via the LS-pin (voltage level sensitive).
Start-up in Aux. Power Mode
As soon as AS2504 is supplied with auxiliary
power at the VDD-pin, the selected signal path
of the speech circuit is switched on. The line
interface circuit (DC-mask and AC-impedance)
is not functional. This on-hook status is
signalled to the internal logic via the LS-pin
(voltage level sensitive).
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 and the voltage at LI is
reduced to a maximum of 3.5V
dd
voltage has reached the operating level of
extraction. The
(DC-mask
and
dd
speech
capacitor will be
AC-impedance).
circuit
is
4/12
The DC characteristic is determined by the
voltage at LI-pin and a 30 resistor between
LI- and LS-pin. It can be calculated by the
following equation: V
t.m. voltage at the LI-pin is 4.5V. The
calculation leads to the following DC
resistances: 330 to 75
15mA to 100mA.
With a HIGH at the MASK-pin, the speech
circuit and other parts of the device, which are
not needed for operation, are in power down
mode in order to save current. The CS-pin is
pulled to V
transistor fully on. This guarantees a low
voltage drop (<1V) at the LI-pin during make
periods of pulse dialling or flash.
2/4 wire conversion
AS2504 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 AS2504 is set to t.m.
1000 . With the external capacitor at CI-pin it
can be programmed complex. With an external
resistor of approx. 1.5k
pin it can be programmed to 600 . Z
33 * 30 .
Side Tone
A good sidetone cancellation can be achieved
by using the following equation:
Z
Transmit path
The gain of the M1/M2 —> LS is set to 37dB.
The input is differential with an impedance of
20k . The soft clip circuit limits the output
voltage at LS to 2V
30µs/6dB and the decay time is 20ms/6dB.
The gain of the M3/M4 —> LS is set to 43dB.
The input is differential with an impedance of
10k . The soft clip circuit limits the output
voltage at LS to 2V
30µs/6dB and the decay time is 20ms/6dB.
BAL
/Z
LINE
ss
= 10
to turn the external shunt
p.
p.
LS
The attack time is
The attack time is
= V
connected to the LS-
at line currents from
LI
+ I
Line
August 1998
* 30 . The
AC(syn)
AS2504
=