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4V on 3V3-SOM!
Added by Nathan Olson 3 days ago
Hello,
Why is 3V3-SOM outputting 4V? Is there a way to change this to 3.3V?
I see that the devkit schematic shows it as 4V, but the datasheet and Carrier Board Design Guide (and the name!) show it as 3.3V. Unfortunately I just received my first boards and they are expecting 3.3V on this pin 
Hello Nathan,
The PMICs on the SOM support changing the output voltage of this pin. The idea was to have it at 3.3V but unfortunately the SOM hangs if this voltage is lower than 4V.
As a result we had to re-spin our development boards and add a Buck-Boost regulator in between this supply from the SOM and the 3V3 net on the baseboard (see U39 of the attached schematic).
Our updated development board schematic can be found here: 80-001777RL-3_SCH_RevB.PDF
We are in the process of re-releasing our datasheets for both the SOM and the development board as well as getting the design guide updated.
I'm not sure where you are in the design process but if these are initial prototype boards we should be able to isolate the SOM supply from the baseboard net and connect an external bench supply so that you can validate the rest of the design.
- Are the two 4V pins (J1 pins F1 and F2) tied directly down to a power plane?
- If not can the connector pins be separated from the downstream components?
- If so then the two pins on the baseboard connector can be bent back and forth until they break off, separating the baseboard net from the 4V SOM supply.
Please let me know if there is anything further I can help with,
Will
Thanks Will. The pins are tied directly to a power plane on my prototype boards, so I'll try breaking the connector pins as you suggest.
Will this issue be fixed in later versions of the SOM, or should I plan on adding a 3V3 regulator to my carrier board?
Unfortunately this cannot be addressed on the SOM as the SOM will hang if this voltage is dropped lower than 4V.
For future baseboard revisions there will need to be a regulator in between the SOM and the downstream components on this net. Please feel free to use the rev 3 dev board as a reference.
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