Can MOSFETS in close proximity create noise on analog readings ?

Other Hardware General Electronics
1

I'm designing a PCB at the moment and I have limited space. I have a few MOSFETS placed closed to my arduino pro mini... I have no formal education or training in hardware design... is this bad practice? Can they create noise on the analog pins or anything like that?

Thanks!

2

Noise occurs not from the MosFets but from changing current (mostly) and changing voltage (somewhat). So if the MosFets are switching while your are making an A/D measurement then Yes it could cause a noise induced error.

It sounds like you already consider moving them with no good options.

Suggestions are:

  1. Stop the MosFet from switching when you have to make an A/D measurement.

  2. Shield the A/D section from the switching section. I can't put a whole PCB layout guide in this post but some things you can do are:
    a) Make absolutely sure the switching grounds and power an not common with the A/D & arduino analog ground anywhere but at the power supply.
    b) Perhaps run a ground trace around the arduino A/D section. May not work here due to the impedances.
    c) You will likely find more suggestions in more depth if you search subjects like PCB layout guides etc.

3

Anything digital can create noise on analog circuits. How sensitive is your analog stuff to that noise though?
(For instance audio circuitry is very sensitive, because the human ear can easily spot a spurious signal 60dB
down from the wanted signal)

For other analog uses it very much depends on how much noise can be tolerated which can vary a lot.

Large currents being switched fast are very hard to shield against because its magnetic fields that are
primarily responsible - keep such noise sources well away from sensitive electronics.

4

Hi,
Don't forget when you are designing a PCB, you have bought a full PCB of copper, so don't try and get most of it etched away.

If possible make your earth/gnd tracks as wide as possible, even going to the edge of the board.
Make any track carrying significant current as wide a possible.

Have you got a prototype working before you commit to a PCB?

Tom... :slight_smile:

5
  1. Did you buy a full PCB of copper?
  2. Which MOSFET did you try?

Try to use the following codes:
30bb - DME
0305
0306
0304
0300
29d1 - Misfire Cyl 5
29d2 - Misfire Cyl 6
29d0 - Misfire Cyl 4
29d9 - something about misfiring
29cc - Multiple Misfire