Panasonic KX-FC971CX-S Service Manual page 172

KX-FC971CX-S / KX-FGA521CX-S
8.13.2. Outline
Cordless Handset consists of the following ICs as shown in BLOCK DIAGRAM (P.171).
· BBIC (Base Band IC): IC900
− − − − FHSS
− − − − All interfaces (ex: Key, Detector Circuit, Charge, DC/DC Converter, EEPROM, LCD)
· RF Module: IC904 (2.4GHz FHSS)
− − − − Tranceiver (TX/RX) including PLL, LNA, LOGIC
− − − − Power amplifier for transmission
· AMP: IC903
− − − − Single OP_AMP for SP
· AMP: IC907
− − − − single OP_AMP for RECEIVER
· EEPROM: IC905
− − − − Temporary operating parameters (for RF, etc.)
8.13.3. Power Supply Circuit/Reset Circuit
Circuit Operation:
When power on the Cordless Handset, the voltage is as follows;
BATTERY(2.2V ~ 2.6V: J1) → L1, D1, Q2 (1.8V) → Q3 (2.7V) → Q1 (4.0V)
The Reset signal generates IC1 (78) and 1.8V.
8.13.4. Charge Circuit
Circuit Operation:
When charging the cordless handset on the Base Unit, the charge current is approx 100mA.
In this way, the BBIC on Cordless Handset detects the fact that the battery is charged.
The charge current is controlled by switching Q5 of Cordless Handset.
8.13.5. Battery Low/Power Down Detector
Circuit Operation:
"Battery Low" and "Power Down" are detected by BBIC which check the voltage from battery.
The detected voltage is as follows;
· Battery Low
Battery voltage: V(Batt) = 3.45V
The BBIC detects this level and "
· Power Down
Battery voltage: V(Batt) = 3.0V
The BBIC detects this level and power down.
8.13.6. Speakerphone and Headset Jack
The hands-free loudspeaker at SP+ and SP- is used to generate the ring alarm. IC2 is used to switch off the telephone
loudspeaker and is used to amplify the signal to drive the hands-free loudspeaker. They are selected using the SP_AMP line
from pin 70 of the BBIC. 2.5mm headset jack is also available.
" starts flashing.
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