Panasonic KX-TCA151AXM Service Manual page 79

22 CIRCUIT OPERATION (CORDLESS HANDSET)
22.1. Outline
Cordless Handset consists of the following ICs as shown in BLOCK DIAGRAM (CORDLESS HANDSET) (P.78).
• • • • DECT BBIC (Base Band 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: IC3
− − − − PLL Oscillator
− − − − Detector
− − − − Compress/Expander
− − − − Amplifier for transmission and reception
• • • • AMP: IC2
− − − − Single OP_AMP for SP
• • • • MIDI (Musical Instrument Digital Interface): IC4
− − − − 16-Tone 32-Poly PCM Sound Generator
− − − − Port (LED direct driver with PWM)
• • • • EEPROM: IC10
− − − − Temporary operating parameters (for RF, etc.)
Refer to EEPROM LAYOUT (CORDLESS HANDSET) (P.91).
22.2. Power Supply Circuit/Reset Circuit
Circuit Operation:
When power on the Cordless Handset, the voltage is as follows;
BATTERY(2.2 V ~ 2.6V: J1) → L1, D1, Q2 (1.8V) → Q3 (2.7V) → Q1 (4.0V)
The Reset signal generates IC1 (78) and 1.8V.
22.3. Charge Circuit
Circuit Operation:
When charging the cordless handset on the Base Unit, the charge current is as follows;
DC+(5.5V ~ 6V) → D1 → R4, R5 → CHARGE+(Base) → CHARGE+(Cordless Handset) → L4 → Q4 → D7→ F1 → BATTERY+
... Battery ... BATTERY- → R43 → GND → CHARGE-(Cordless Handset)→ CHARGE-(Base) → GND → DC-(GND)
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.
Refer to Fig.101 in Power Supply Circuit (P.76).
22.4. 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)
The BBIC detects this level and "
• • • • Power Down
Battery voltage: V(Batt)
The BBIC detects this level and power down.
Refer to Adjustment (Cordless Handset) (P.66).
22.5. 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.
2.3V ± 50mV
" starts flashing.
2.2V ± 50mV
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KX-TCD530AXM / KX-TCA151AXM