Panasonic KX-TG9120FXS Service Manual

Contents

12KX-TG9120FXS/KX-TGA910FXS4.4. Circuit Operation (Handset)4.4.1. OutlineHandset consists of the following ICs as shown in Block Diagram (Handset) (P.11).• 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, Flash ROM, SRAM, LCD)• FLASH MEMORY (substitute EEPROM): IC2- Source program data and temporary user data are stored• SRAM: IC3- Application data and code are temporary stored• RF Module: IC20- PLL Oscillator- Detector- Compress/Expander- Amplifier for transmission and reception4.4.2. Power Supply Circuit/Reset CircuitCircuit Operation:When power on the Handset, the voltage is as follows;BATTERY(2.2 V ~ 2.6 V: BAT+) → F1, L1, D1 → Q7 (1.8 V), Q8 (3.0 V), Q1 (4.0 V)The Reset signal generates IC1 (120 pin) and 1.8 V.4.4.3. Charge CircuitCircuit Operation:When charging the handset on the Base Unit, the charge current is as follows;DC+(6.5V) → R55, R56 → CHARGE+(Base) → CHARGE+(Handset) → Q10 → D10 → F1 → BAT+ ... Battery ...BAT- → R43 → 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 Q10 of Handset.Refer to Fig.101 in Power Supply Circuit (P.9).4.4.4. Battery Low/Power Down DetectorCircuit Operation:“Battery Low” and “Power Down” are detected by BBIC which check the voltage from battery.The detected voltage is as follows;• Battery LowBattery voltage: V (Batt) 2.25V ± 50mV (When the back light disappeares)The BBIC detects this level and “ ” starts flashing.• Power DownBattery voltage: V (Batt) 2.00V ~ 2.05VThe BBIC detects this level and power down.4.4.5. SpeakerphoneThe hands-free loudspeaker at SP+ and SP- works as a ringer/alarm as well.