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By cdwilson
#223986
The RP2040 MicroMod shorts RTC_3V directly to 3.3V. Can someone explain why these are shorted together?

2021-03-12_22-34-21.png

When 3.3V_EN is disabled on a carrier board, won't this cause the RTC battery to attempt to backfeed any devices on 3.3V rail (including devices on the carrier board 3.3V)?

The MicroMod specs for RTC_3V say:
3V provided by external coin cell or mini battery. Max draw=100μA. Connect to pins maintaining an RTC during power loss. Can be left NC.
The 3V3_LED on the carrier board by itself will exceed 100μA at 3V. Doesn't this violate the above spec for RTC_3V?
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User avatar
By adam.g
#223991
Hi @cdwilson,

I don't yet have an RP2040 Processor, but I'd be also curious to learn why RTC_3V is shorted 3.3V. I recall the RTC draining quickly was identified by a user in a GitHub issue investigating other power-related problems with the Artemis Processor and MicroMod Data Logging Carrier Board:

https://github.com/sparkfun/MicroMod_Da ... -734486555

The Artemis Processor looks to have a diode on the 3.3V pin of the MicroMod connector but this isn't included on the RP2040 Processor.

Image

That being said, even with this diode, I've found that the RTC battery still drains rapidly and cannot be relied on to keep the Artemis Processor's RTC clock powered when unplugged.

Cheers,
Adam
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