21KX-TG4753B/KX-TG470B/KX-TGA405B4.7.3. Charge CircuitCircuit Operation:When charging the handset on the Base Unit, the charge current is as follows;DC+(6.5 V) → F301 → R371 → R372 →CHARGE+(Base) → CHARGE+(Handset) → Q4 → D7→ F1 → BATTERY+... 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 Q9 of Handset.Refer to Fig.101 in Power Supply Circuit/Reset Circuit (P.12).4.7.4. 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) 2.35 V ± 50 mVThe BBIC detects this level and " " starts flashing.• Power DownBattery voltage: V(Batt) 2.0 V ± 50 mVThe BBIC detects this level and power down.4.7.5. SpeakerphoneThe hands-free loudspeaker at SP+ and SP- is used to generate the ring alarm.4.8. Circuit Operation (Charger Unit)Charge control is executed at handset side so that the operation when using charger is also controlled by handset.Refer to Circuit Operation (Handset) (P.20)The route for this is as follows: DC+pin of J1(+) → F1 → R1 → CHARGE+pad → Handset → CHARGE-pad → DC-pin of J1(-).CHG +Q4R4 47KR610KQ9GNDR7 CHG DET (34)CHG CTRL (32)100KCHG -GNDBATT +BATTERY2CELLBATT +GNDBBICIC1Q2R8Q3C27R2R9R2R1 TP1TP2D1J1AC AdaptorF1
