1

I'm currently designing a PCB with 4 Layers. The stack up is as follows:

Signal - DGND Plane - AGND Plane - Signal.

There are a ton of components connected to the DGND Plane, and I know that for using the MAX6675 the slightest interference can cause very different results. So I'm thinking, when I connect the chip to analog ground plane, to minimize interferences more. I don't know if the question is dumb because I'm not that long in this game. I would appreciate a opinion from someone with slightly more knowledge :)

To the analog plane are currently connected my 3.3V buck/boost converter, and the camera interface.

Current configuration is as follows:

enter image description here

Cem Pamir Bana
  • 107
  • 5
  • You may want to rethink the DGND/AGND planes, high frequencies will shoot right through because of the capacitive coupling thus negating the whole idea of keeping them separate. – pipe Mar 30 '23 at 19:16
  • Uff okay yeah I could've thought of that. Can you explain a little more and what would you recommend? – Cem Pamir Bana Mar 30 '23 at 19:22
  • 1
    That's a huge topic, and I know 0.1% of if. My favourite resources are two physical books: _High Speed Digital Design: A Handbook of Black Magic_ and _Electromagnetic Compatibility Engineering_. – pipe Mar 30 '23 at 19:42

1 Answers1

1

I would connect the MAX6675 GND to an analog ground plane, if you decide to have one. The digital signals can tolerate several hundreds of millivolts difference.

Apart from being standard practice in hybrid (digital+analog) ICs, the pin layout puts the ground pin on the same side as the analog part.

pipe
  • 13,748
  • 5
  • 42
  • 72
  • Okay so I connect both the MAX6675 GND to the Analog Ground Layer and the T- Pin? Can you maybe tell me, if it makes sense to seperate AGND and DGND Planes in two different layers? Is it a awful idea? – Cem Pamir Bana Mar 30 '23 at 19:42
  • 1
    @CemPamirBana I would not do it as separate _planes_ unless I have a lot of planes and can put something else in between, but it sometimes makes sense to separate them physically on a single plane. As I wrote in a comment, the topic is huge and interesting and there are probably hundreds of questions here about separate analog/digital ground! Careless splitting of a ground plane may even be worse than just using a single solid one. https://electronics.stackexchange.com/a/306896/91862 and https://electronics.stackexchange.com/a/118484/91862 looks promising but there are many more. – pipe Mar 30 '23 at 19:50