RTC.CTRL.SPLITPOWER bit cannot be changed?

Hi,

We found that when L138’s RTC module is supplied at L14 pin “RTC_CVDD” by external battery which is separate from the main battery, the RTC continues to run even when the main battery is removed and the other parts are completely powered off. If we wait for some time and supply the power to other parts again, and turns on, from emulator we can read the RTC values exactly correspond to the time elapsed between this interval.

This observation seems to suggest that the RTC already has independent power supply from the other parts. Then why does SPRUH77 section “28.2.3 Isolated Power Supply” / “28.2.3.1 Split-Power Circuitry” and “28.3.14 Control Register (CTRL)” still document about CTRL.SPLITPOWER bit? I have also tried to clear this bit although I cannot verify if the operation succeeded because it always reads back 0, but after this and then removing the power and then supplying power and connect again, we can see RTC values were still preserved and has been continuously counting.

Some posts seems to suggest that the SPLITPOWR bit is internally tied high on version 2+ devices.

The RTC SPLITPOWER bit is permanently tied high internally on Silicon Revision 2 and beyond. Also, you can take advantage of the 1.25V-1.32V overlap between 1.2V Max and 1.3V Min to share a single supply.

-Tommy

 

The typical power difference between SPLITPOWER 0 vs 1 is unknkown. The bit is permanently tied high on silicon revision 2.0 and beyond so we shouldn't have to worry too much about that. Can you check to make sure that the normal CVDD 1.2V supply is actively driven or pulled to GND and is not left floating?

-Tommy