SAMD21 and EM noise

[anvoice]

My SAMD21 will possibly face some EM noise (motor some distance away and a spinning magnet a few millimeters from the chip), so I was looking at the datasheet wondering which protection measures I need to implement.

Power supply connections: my power is coming from a buck converter placed close to the chip, so I would like to know which decoupling capacitors I should use (Section 42, page 1152 of SAMD21 datasheet). Specifically, there is no GNDANA pin on the SAMD21E I'm using, or VDDIO, so clearly I can't place capacitors there. Is a decoupling capacitor on VDDIN still needed given the buck output is very close?

Reset RC filter: is that really needed? When the chip will be programmed, the motor will be off and the normally spinning magnet stationary, so I don't envision much noise at that time. Should I still implement the RC filter on the reset pin?

Thanks in advance.

[ataradov]

I would at least place a footprint for the second capacitor.

On the reset pin you may not need the RC filter, but external pull-up resistor is highly recommended in high EMI environments.

[anvoice]

Do you mean the capacitor going to VDDIN (the one I labeled C4 in the attached picture)? What about the inductor and the 10uF capacitor (C5) between 3.3V and ground?

So the EMI might trigger the Reset pin despite the internal pull-up. Is 1K a good value to use for the Reset pull-up, or should something weaker/stronger be used?

[ataradov]

C5 here really represents your capacitor on the regulator output. And inductor is there to cleanup VDDANA. It is there for analog performance, but in a device with combined power supplies pins and noisy environment you should not expect excellent analog performance anyway.

In general all available supply pins should get a separate capacitor.

Internal pull-up is around 100 K. Even 10K external resistor will work. For 1K you would need to check if it will work with your programming tools. Some may have current limiting on the output and may not be able to fully drive it to ground.

[anvoice]

Got it. That includes VDDANA I'm guessing?

[ataradov]

Got it. That includes VDDANA I'm guessing?

if you are talking about the bypass capacitor, then yes.

[T3sl4co1l]

Yes, it is alright to share bypass caps between nearby pins/devices.

Tim