SIGMA BENEFON TDP-52-SN3 - Manual (Page 167)

27.1.1999
Xo0245e4_fm5.fm 6
Product: LIF-40 (Line Interface) / YO0245
While Q100 is conducting, the energy flows through resistor R108 to the coil L100.
When the switch Q100 stops conducting, the energy received by L100 is discharged
through the rectifier diode D100 to the capacitor C106. The fet is protected by C122
and C123 against excessive voltage peaks, while L101/C107 functions as a low-
pass filter for filtering the ripple voltage. The output voltage in capacitor C107 pins
depends on the RINGON signal mode, being approx 50V in the ring mode (RIN-
GON=1) and 15 ±3 VDC in the normal mode (RINGON=0).
9.1.3.7 Current Sink
The current passing through the two-wire data terminal is kept constant by a con-
stant-current load formed by I103A, Q101 and Q102. The closed-loop current is 25
±5 mA.
9.1.3.8 Connection of I2C
The control connection is made with the I2C circuit I104, which controls the switch-
ing-on of the voltage, call and free/reserved tone according to the commands com-
ing from the portable. Data received by the portable is a HOOK mode, the change of
which is identified by the portable as interruption.
In addition, one of the I104 inputs (pin 7) has been connected to the ground so that
the portable receives interruption every time the voltage is switched on.
9.1.3.9 Free/Reserved Tone
The free/reserved tone is connected by transistor Q106 to a filter consisting of the
operation amplifier I100B. In this filter, the tone is reduced to a suitable level, and the
square wave received from Q106 is made more gentle.
9.1.3.10 Line Switches
The double fet switches Q107/Q110 and Q109/Q108 form the line switches which
switch on the ring voltage to the two-wire connection. While conducting, Q104
switches the double fet Q107/Q110 to conduct, whereby the current passes in line
connection from pin LB to pin LA. While conducting, Q103 switches the double fet
Q109/Q108 to conduct, whereby the current passes in line connection from pin LA to
pin LB.
Q111 ensures that only one of the switches Q103 and Q104 is conducting and that
R144/R145 form the voltage distribution which will prevent the VDD from overflowing
through VCC 1102 in standby mode.
9.1.3.11 HOOK Detection
HOOK detection is carried out by operation amplifier I103B which controls the data
terminal current coming from resistors R123/R124. The threshold level is changed
according to the power mode in order to detect the OFF-HOOK mode using a low
battery voltage and to make sure the OFF-HOOK mode is not switched on too easily
during a call.