PCB Layout Help

[Rendman]

Hi all,

I unfortunately did not remember to take waveform shots when I was scoping the signal, otherwise I could have shown you exactly what I was seeing. It's wasn't really a sine wave, as I said it resembled a spike that happened about every 52 KHz or so. The "length" of the spike was very short, maybe not in the nanosecond range, i don't remember because I was not trying to measure it. That is something I will certainly pay better attention to in the future,

On a another note, I have a modified layout here, and was wondering if you nice folks might take a look and tell me if there are any things you would change about it.

Thanks,
JD

 

[KrisBlueNZ]

If you put your scope on the board again, try an experiment. Without moving the ground clip of your scope, remove the scope probe from the point in the circuit where you see the 52 kHz signal and touch it on the ground clip. If you see a similar signal, you can assume that it's just common-mode noise being picked up by the scope, not an actual differential-mode signal that could interfere with the oscillator.

Another thing to try is to move the probe, and especially the ground wire from the scope probe, closer to, and further away from, inductors in the power supply, especially the main switching inductor. The alternating magnetic field from an inductor or a transformer can induce a voltage into the ground wire which the scope will detect as a signal.

 

[Arouse1973]

I can't see your guard ring connected to anything? Is this right?
Adam

 

[Arouse1973]

If you put your scope on the board again, try an experiment. Without moving the ground clip of your scope, remove the scope probe from the point in the circuit where you see the 52 kHz signal and touch it on the ground clip. If you see a similar signal, you can assume that it's just common-mode noise being picked up by the scope, not an actual differential-mode signal that could interfere with the oscillator.

Another thing to try is to move the probe, and especially the ground wire from the scope probe, closer to, and further away from, inductors in the power supply, especially the main switching inductor. The alternating magnetic field from an inductor or a transformer can induce a voltage into the ground wire which the scope will detect as a signal.

Good advice Kris.
Adam

 

[Rendman]

Umm, yes. I realized that after I posted the pictures. I have it connected to the bottom ground plane by via.

Additionally, I damaged the uC on the board that I was using before I got to try Kris's suggestion. I am very interested to try it, and will order some new controllers and build up a board minus the switchmode regulator for now. If I get it to oscillate I will install the switcher and try what Kris said.

I will report back here with results.

Thanks guys.

 

[Arouse1973]

Umm, yes. I realized that after I posted the pictures. I have it connected to the bottom ground plane by via.

Additionally, I damaged the uC on the board that I was using before I got to try Kris's suggestion. I am very interested to try it, and will order some new controllers and build up a board minus the switchmode regulator for now. If I get it to oscillate I will install the switcher and try what Kris said.

I will report back here with results.

Thanks guys.

Good Luck.