Panasonic KX-FC255CX-S, Service Manual, Page: 46 / 256

46
KX-FC255CX-S
6.13.2. Circuit Operation (Cordless Handset)
6.13.2.1. Outline
Handset consists of the following ICs as shown in Block Diagram (P.45).
• DECT BBIC ( B ase B and IC): IC1
- All data signals (forming/analyzing ACK or CMD signal)
- All interfaces (ex: Key, Detector Circuit, Charge, DC/DC Converter, EEPROM, LCD)
• RF Module: IC4
- PLL Oscillator
- Detector
- Compress/Expander
- Amplifier for transmission and reception
• EEPROM: IC3
- Temporary operating parameters (for RF, etc.)
6.13.2.2. Power Supply Circuit/Reset Circuit
Circuit Operation:
When power on the Handset, the voltage is as follows;
BATTERY(2.2 V ~ 2.6 V: J1)
→
F1, L1, D1
→
Q2 (1.8 V), Q3 (2.5 V), Q1 (4.2 V)
The Reset signal generates IC1 (53 pin) and 1.8 V.
6.13.2.3. Charge Circuit
Circuit Operation:
When charging the handset on the Base Unit, the charge current is as follows;
DC+(6.5V)
→
R55, R56
→
(Base)
→
(Handset)
→
L4
→
Q4
→
D7
→
F1
→
... Battery ...
BATTERY-
→
R45
→
GND
→
CHARGE-(Handset)
→
CHARGE-(Base)
→
GND
→
DC-(GND)
In this way, the BBIC on Handset detects the fact that the battery is charged.
The charge current is controlled by switching Q5 of Handset.
6.13.2.4. 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) 2.25V ± 50mV
The BBIC detects this level and "
" starts flashing.
• Power Down
Battery voltage: V(Batt) 2.00V ~ 2.05V
The BBIC detects this level and power down.
6.13.2.5. Speakerphone
The hands-free loudspeaker at SP+ and SP- works as a ringer/alarm as well.
6.13.3. Circuit Operation (Charger Unit)
6.13.3.1. Power Supply Circuit
The power supply is as shown.