SNVS rail powering main rail in "RTC only" state

Technical Support
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Hello Toradex team,

I’m using I’m using IMX6ULL 256 MB V1.1A SoM.

I have a permanent 3,3V on VCC_BATT pin (SODIMM 40) to keep the time.

Basically, my issue is that when I remove all power rails from the module, except VCC_BATT, my main rail is still powered between 3,0V and and 3,2V (it powers other modules on our main board).

Cutting the supply track to VCC_BATT pin fixes my issue, but this not acceptable, it just shows the issue happends inside the SoM.

I have verified, as you recommend it, that all my SNVS pins with any attached load are set to 0 before entering the “RTC Only” state, but it doesn’t change anything.

I also read your errata file : https://docs.toradex.com/105707-colibri-imx6ull-errata.pdf
How does the switch between SNVS rail ans main rail that you added in version 1.1 works ? Can this switch keep powering main rail with SNVS one ? Or any other module (such as wifi) that still powered by SNVS rail and sends back this power in main rail ?

Best regards,
Willy

1 Like
2

Hello,
which carrier board are you using? Are you using a custom carrier board?

Best Regards,

Matthias Gohlke

3

Hello,

I’m using a custom carrier board.

Best regards,
Willy

1 Like
4

hello Willy,

can you share a quick snippet of your schematic covering the coin cell batt part?
Do you have the diodes to prevent back feeding?

Best Regards,

Matthias

5

Mattias,

Ananas - Page 3
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Here is a quick snippet of my schematic covering the coin cell batt part.

I rode about the diode in the datasheet. As far as I understood, I have to place those diodes after the SNVS pins.

image
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Since all the SNVS pins are floating in my schematic, I didn’t use any diodes.

Best regards,
Willy

1 Like
6

Hello,

I don’t see a Battery in your schematic and either any diode. So I can only assume things here.
The AP7370-33W5-7 is an LDO.

Here is a little illustration of what I mean.
Screenshot from 2022-11-14 18-18-05

You can send your schematic to support@toradex.com and include this ticket as a link.
We can also set up a zoom or teams call.
Best Regards,
Matthias Gohlke