Rtc Backup Circuit - Panasonic KX-MB2085CXW Service Manual

KX-MB2085CXW/KX-MB2090CXW
6.3.2.

RTC Backup Circuit

1. Function
This unit has a lithium battery (BAT300) which works for the Real Time Clock IC (RTC: inside IC300).
The RTC continues to work, backed up by a lithium battery even when the power switch is OFF.
*RTC:(Real Time Clock)
Chip for the clock mounted on the motherboard.
Receiving power supply to operate even while the power is off unlike the other chips on the motherboard.
2. RTC Inside (IC300) Backup Circuit Operation
When the power switch is turned ON, power is supplied to the RTC (inside IC300). At this time, the voltage at pin AF7 of the
IC300 is +3.3V. When the power switch is turned OFF, the BAT300 supplies power to RTC through DA300.
When the power switch is OFF and the voltage of +3.3V decreases, pin AF7 of RTC (IC300) becomes roughly the same volt-
ageas the battery voltage. RTC goes into the backup mode, in which the power consumption is lower.
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