Hi,
Again the topic which has already been discussed several times in this forum. I just want to share my experience and perhaps help other users having difficulties.
The DK's voltage margins when being supplied with 1.8V are really tight. With my external 1.8V being slight low (-0.9%: 1.784V), the interface MCU resets sporadically. Here is why (I think, at least) using this MCU datasheet:
- VDD_SAM measured at 1.764V (-20mV) due to voltage drop across voltage follower and different load switches on the DK.
- MCU core voltage measured at 1.605V (-179mV) under load (debugging).
- MCU core regulator dropout is <150mV (datasheet)
MCU reset falling threshold: <1.62V with 1.50V nominal (there is a value swap in the SAM datasheet, but this is the value which makes sense). So the minimum VDD_SAM allowed in this configuration is 1.77V with no margins at all.
In my case, depending on the fabrication parameters of the MCU, it could already reset in the static case. With typical parameters, add any dynamic voltage drop and you get sporadic resets.
I added two 100uF ceramic capacitors, one across C38 and the other across C39 to reduce at least the dynamic voltage drops. The board appears to be more stable now. If I see further resets, I need to hunt for a 1.8V regulator with a positive tolerance.
Best regards,
Norbert