Panasonic KX-FP701LA Service Manual page 21

6.3.7. RTC Backup Circuit
1. Function
This unit has a lithium battery (BAT401) which works for Real Time Clock IC (RTC: inside IC1).
The RTC continues to work, backed up by a lithium battery even when the power switch is OFF.
The user parameters for autodial numbers, the system setup data and others are in the FLASH MEMORY (IC6).
2. RTC Inside (IC1) Backup Circuit Operation
When the power switch is turned ON, power is supplied through Q7 to the RTC (inside IC1). At this time, the voltage at pin 14
of the IC1 is +2.5V. When the power switch is turned OFF, the BAT401 supplies power to RTC through D407 and Q505. The
voltage at pin 14 of IC1 is about +2.2V. When the power switch is OFF and the voltage of +3.3V decreases, pin 14 of RTC
(IC1) becomes roughly the same voltage as the battery voltage. RTC goes into the backup mode, in which the power con-
sumption is lower.
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KX-FP701LA