as2522bq austriamicrosystems, as2522bq Datasheet - Page 5

• Manufacturer Part Number: as2522bq
• Description: Telephone Line Interface And Speakerphone Circuit
• Manufacturer: austriamicrosystems

Data Sheet AS2522B
Functional Description
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.
The DC characteristic is determined by the voltage at LI-
pin and a 30
calculated by the following equation: V
30 . V
2/4 wire conversion
AS2522 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 AS2522 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
connected to the LS-pin it can be programmed to 600 .
Side Tone
A good side tone cancellation can be achieved by using the
following equation:
Z
Transmit path
The gain of the M1/M2
can be changed by programming from +30dB to +45dB in
1dB steps (Register Txgain). The input is differential with
an impedance of 10k . The soft clip circuit limits the
output voltage at LS to 2V
The gain of the M3/M4
This gain can be changed by programming from +39dB to
+54dB in 1dB steps. The input is differential with an
impedance of 10k . The soft clip circuit limits the output
voltage at LS to 2V
Receive path
The gain of the LS
This gain can be changed by programming from -6dB to
+9dB in 1dB steps (Register Rxgain). The receive input is
the differential signal of RI and STB. The soft clip circuit
Revision 3.4
BAL
/Z
LINE
LI
can be programmed to be 3.5V or 4.5V.
= 10
resistor between LI- and LS-pin. It can be
p
. There is no LLC for this path.
RO receive path is set to +1dB.
p.
LS is set to +37dB. This gain
LS is set to +46dB.
There is LLC for this path.
LS
= V
LI
+ I
Line
*
limits the output voltage at RO to 1V
distortion and acoustic shock. There is LLC for this path.
The gain of the LS
+29dB. This gain can be changed by programming from
+22dB to -37dB in 1dB steps. The user can also change
the gain via Register VOL (See section "Handsfree"). The
receive input is the differential signal of RI and STB. The
soft clip circuit limits the output voltage at LO1 of LO2 to
1V
is optional LLC for this path.
Line Loss Compensation
The line loss compensation is programmable (Register
0x0C). When it is activated, the transmit and receive gains
for both I/O’s are decreased by 6dB at line currents from
20mA to 50mA or from 45mA to 75mA.
Handsfree
The handsfree function allows voice communication without
using the handset (full 2-way speaker phone). Two voice
controlled attenuators prevent acoustic coupling between
the loudspeaker and the microphone. The voice switching
circuit has three states, namely idle, transmit or receive. In
receive mode the attenuation of the receive path and the
transmit path can be controlled by Register VOL between
0dB and -20dB. The following table shows how voice
switching is controlled
p.
It prevents harsh distortion and acoustic shock. There
LO1/LO2 receive path is set to
p.
It prevents harsh
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