Rtc Backup Circuit - Panasonic KX-FP342CX Service Manual

becomes low level.
The terminal of the 'WDERR' signal is connected to the reset line,
so the 'WDERR' signal works as the reset signal.

7.3.7. RTC BACKUP CIRCUIT

1. Function
This unit has a lithium battery (BAT501) which works for Real Time
Clock IC (RTC: inside IC501).
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 ROM (IC523).
2. RTC Inside (IC501) Backup Circuit Operation
When the power switch is turned ON, power is supplied through
Q506 to the RTC (inside IC501). At this time, the voltage at pin 14
of the IC501 is +2.5V. When the power switch is turned OFF, the
BAT501 supplies power to RTC through D503and Q506. The
voltage at pin 14 of IC501 is about +2.2V. When the power switch is
OFF and the voltage of +3.3V decreases, pin 14 of RTC (IC501)
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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