KX-TCA355RU - Panasonic PBX Service Manual (repair manual). Page 7

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Handset consists of the following ICs as shown in Block Diagram (Handset) (P.6).

• DECT BBIC (Base Band IC): IC201

- All data signals (forming/analyzing ACK or CMD signal)
- All interfaces (ex: Key, Detector Circuit, Charge, DC/DC Converter, LCD)

Include EEPROM and Flash memory
EEPROM stores the temporary operating parameters (for RF, etc.)

• AMP: IC401

- Single OP_AMP for SP

• MIDI: IC301

- 16-Tone 32-Poly PCM Sound Generator
- Port (LED direct driver with PWM)

• RF  Block

- IC601

PLL Oscillator
Detector
Compress/Expander
Amplifier for reception

- IC602

Amplifier for transmission
Power control

When power on the Handset, the voltage is as follows;
BATTERY(3.5V~4.2V: Battery+) 

→ Q104 (1.8V)

BATTERY(3.5V~4.2V: Battery+) 

→ Q105 (2.7V)

The Reset signal generates IC201 (78) and 1.8V.

When charging the handset on the charger, the charge current is as follows;
DC+(9V~10V) 

→ IC601(6) → IC601(2) → L601 → JT601(Charger) → JT101(Handset) → L101 → Q101→ D102 → BAT-

TERY+... Battery... BATTERY- 

→ R115 → GND → L102→ JT102(Handset) → JT602(Charger) → R616, R617, R618, R619 →

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 Q101 of Handset.

"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)   3.5V ± 50mV

The BBIC detects this level and "

" starts flashing.

• Power Down

Battery voltage: V(Batt)   3.3V ± 50mV
The BBIC detects this level and power down.

The hands-free loudspeaker at CN401(1) and CN401(2) is used to generate the ring alarm. IC401 is used to switch off the tele-
phone 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.