What's the conditions about VDD(REG)(3V3) and VBAT on LPC1778?

[zhiguozhai]

In the datasheet page66:The device core power(VDD(REG)(3V3)) is used to operate the RTC whenever VDD(REG)(3V3) is present. There is no power drain from the RTC battery when VDD(REG)(3V3) is at nominal levels and VDD(REG)(3V3) > VBAT.

But in LPC178x/7x User manual page785:Uses power from the CPU power supply whenever it is greater than VBAT.
So If both VDD(REG)(3V3) and VBAT are present,and VBAT>VDD(REG)(3V3),which is the power supply for RTC?

[soledad]

Hi,

This device implements a separate VBAT power domain in order to allow turning off power to the bulk of the device while maintaining operation of the Real Time Clock. The VBAT pin supplies power only to the RTC domain. Whenever the device core power is present, that power is used to operate the RTC, causing no power drain from a battery when main power is available, check the following figure.

I hope this helps!!

Have a great day,
Sol

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