Panasonic KX-FL612CX Service Manual page 156

KX-FL612CX / KX-FL612CX-S
7.3.2. RTC BACKUP CIRCUIT
1. Function
This unit has a lithium battery (BAT600) which works for the Real Time Clock IC (RTC: inside IC606).
The RTC continues to work, backed up by a lithium battery even when the power switch is OFF.
2. RTC Inside (IC606) Backup Circuit Operation
When the power switch is turned ON, power is supplied to the RTC (inside IC606). At this time, the voltage at pin 10 of the
IC606 is +3.3V. When the power switch is turned OFF, the BAT600 supplies power to RTC through D602. The voltage at pin
10 of IC606 is about +2.5V. When the power switch is OFF and the voltage of +3.3V decreases, pin 10 of RTC (IC606)
becomes roughly the same voltage as the battery voltage. RTC goes into the backup mode, in which the power consumption
is lower.
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