low noise PIC MCU?

[CopperCone]

http://www.microchip.com/design-centers/emc

They have some before and after spectrums.

do you think a PIC18F4685 falls into the before or after? What similar PIC can I choose that has the "after" specification?
Does it go by manufacturing date? Or product line?

[Kleinstein]

How a chip is made can have quite an effect on EMI. So a µC that produces less RF emissions is a good idea to make it easier to meet the EMC requirements. You should still use a good layout, but could get away with a few saved caps or without the choke. Eve if this only helps to pass the EMC test more often on the first attempt, it helps.

An example for a chip that is not very EMI friendly is the old NE555 - during switching it produces quite some cross conduction current pulse on the supply and this way can cause quite some trouble. In this case it's not so much EMC relevant emissions, but interference with other parts of the circuit. Also the case / pinout can be a factor: The old way of having the supply pins at the far ends of a DIP40 is kind of a bad idea - so newer chips changed that to supply ad adjacent pins in the middle.

With the PICs this might be more like a problem with some older PICs that produce a relatively high amount of emission - using CMOS that can run over a relatively large supply range is kind of pointing that way. So it could be as well a poor older PIC.

[Andreas]

They have some before and after spectrums.

Before: typical emissions by your design before you have visited their EMC-seminar
after: that what you can reach after having visited the seminar.

best regards

Andreas

[Leo Bodnar]

I don't know if you are aware but a lot of latest PIC18s have output buffers slew rate control and the default power-up setting is reduced slew rate.

This will magically reduce EMI for those who have no idea.

It will also stop an older high performance design working if you just drop the new chip in.  Luckily it's just a register setting and it's good to have a choice.

Leo

[CopperCone]

Even if you use filters its still better if the noise is not there in the first place. It says it was measured in a tem cell. You would need to surrround the chip with filters to prevent this noise. I am doing sensitive analog work so the lilly will be gilded anyway, i dont see it different then choosing a low noise opamp.

[chris_leyson]

Given that the PIC18F4685 is an older generation 5V part and a lot of the newer generation 3.3V parts like PIC24 and DSPIC run the core at 2.5V and the fact that the PIC18F4685 has 25mA pin drive capability I would say it falls into the before catagory.