SA2532
FUNCTIONAL DESCRIPTION
Power On Reset
The on chip power on reset circuit monitors the supply voltage (V
DD
). When V
DD
rises above
approx. 1.2V, a power on reset occurs to assure correct start-up and the RAM is cleared.
DC Conditions
The normal operating range is from 13mA to 100 mA. Operating range with reduced
performance is from 5mA to 13mA. In the operating range all functions are operational.
In the line hold range from 0 to 5 mA the device is in a power down mode and the voltage at
LI is reduced to maximum 3.5V.
The dc characteristic (excluding diode bridge and Pulsing transistors) is determined by the
voltage at LI and the resistor R1 as follows:
VLS = VLI + I
Line
.R1
The voltage at LI is 4.5V.
During pulse dialling the speech circuit and other parts of the device not required are 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 Characteristic or Output impedance of the SA2532 is set within the IC and adjusted by
Mask Options. Available options are for 600Ω and 1000Ω. When the 1000Ω option is selected
then a capacitor may be added to the circuit at pin CI to add a reactive element and make the
output impedance complex.
Oscillator
All the Timing Functions of the SA2532 are based on a Clock Frequency of 3.58MHz. A crystal
or ceramic resonator of this frequency should be connected to the OSC pin. In practise minor
deviations from the nominal frequency may occur due to the characteristics of the frequency
reference device used and so it is recommended that care is taken in the selection of
components.
In some cases a small value capacitor (
≤47pF)
may have to be connected in parallel with the
Frequency Reference to ensure start-up and/or operation at the nominal frequency.
Speech Circuit
The speech circuit consists of a transmit and a receive path with soft clip, mute, line loss
compensation and side tone cancellation.
Transmit
The gain of the transmit path is 35 dB for M1/M2 to LS (see test circuit figure 5). The
microphone input is differential with an input impedance of 25 kΩ.
The soft clip circuit limits the output voltage at LI to 2.0V
PEAK
. The attack time is 30µs/6dB
and the decay time is 20 ms/6 dB. When mute is active, during dialling or after pressing
the MUTE key, the gain is reduced by > 60 dB.
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SAMES [ SAMES ]
