i.mx6ul brownout voltage

[vale90]

Hello,

We are using a Phytec SOM which includes i.mx6ul. 

We use supercapacitor at the 3.3V supply of the SOM module.
When mains power is OFF; voltage goes down slowly and it gots stuck at lower than 3V levels.
Problem is; it doesn't reboot after power is ON (3.3V) again!

Note: If voltage goes lower than 1V; it works fine after power is ON again.
Note-2: We tried supplying the SOM with an adjustable DC source-only and removed supercaps. Same thing happens. Issue is not related with supercaps. It is something where some voltage levels makes the SOM stuck.

We couldn't solve this blind zone.

We trying to set-up brownout but we couldn't reach enough information. Would brownout solve this issue?

Thanks for your help.

[vale90 · Accepted solution]

Thank you Yuri.

We found the problem was boot SD card itself.

Some SD cards cause this problem (stucks at some voltage levels).

We insterted a new one; it didn't create this problem.

[Yuri]

@vale90 
Hello,

   the problem here concerns residual voltage of i.MX pins. This 
violates i.MX power up sequence.
  On the EVK discharge circuits (controlled by signal DISCHG_EN) are applied 

https://www.nxp.com/webapp/Download?colCode=MCIMX6UL-EVK_DESIGNFILES

Regards,
Yuri.