SIGMA BENEFON TDP-52-SN3 - Manual (Page 140)

27.1.1999
8dds50gb_fm5.fm 8
Product: DDS-50(Office set) / YO0311
Spare battery discharge is controlled with signal D2. High level on output switches
transistors Q287 and Q285 into conducting state, which makes current flow through
resistors R280-283 and transistor Q285. Nominal value of discharge current is ~ 180
mA.
Signal D3 is used to turn on/off the detect current supply I234. The logic high signal
turns the regulator off and logic low on. When the phone is present, the state of this
pin is usually low. Only when the charge control line I0 has a value greater than 4
VDC does it have a high output. Regulator I234 output is ~ 7 VDC, Imax 150 mA.
Charge indicator leds are turned on using the signals D4 to D7. Logic high signals
switch transistors Q303, Q305, Q313 and Q315 into conducting state. The emitter
pins of the transistors are directly connected to the anode pins of the leds.
8.1.3.3 Audio
The signal P1 (HF_OFF) of the I2C circuit I203 is used to control the analog
switches I435 and I437. Q512 inverts this signal for switch I484. The inverted signal
is also used for controlling the MUTE pin of the power amplifier I528. Low level sig-
nal turns MUTE on and high level signal (3 V) off respectively. Switch I481 and
MUTE pin of the power amplifier I499 are controlled with signal HS_CTRL. This sig-
nal is inverted from the DC level of the handset earphone signal.
The HOOK signal is controlled with the handset. Whenever the handset has been
placed on the holder, the DC level of the HS_ERP signal should be ~ 4,2 V. Remov-
ing the handset from the holder makes the voltage drop to a value of 0,4 VDC. This
signal and the transistors Q474 and Q475 are used to control the DC level of the
EXTERP signal. ON_HOOK level is ~ 5 VDC, OFF_HOOK ~ 0,6 VDC.