Multi-Mixed Signals

[Mikebits]

I want to get some opinions and ideas on this. I have a design that has several signal types. A PSoC micro clocked at 24MHz (digital junk), some very sensitive analog signals (uA) current sourced, and audio at 1W. I have partitioned power with analog and digital, along with grounds. Now my concern is the audio, running class D audio at ~1W. My worry is that the audio may cross over into my more sensitive analog sections. So I am thinking another ground for the audio. What about power (I would hate to use another Vcc supply)?
Your thoughts? Also, audio quality is not key concern.
----------------Edit----------------------------------------------------------------
Forgot to mention, the audio devices are: LT6350 https://www.linear.com/product/LT6350
TPA2013 https://www.ti.com/product/tpa2013d1

 

[ronsimpson]

Assume there is only one Vcc:
I would add a inductor in between Vcc, and VccAudio . A class D amp will make noise at the switching frequency.
You might put the audio in a corner of the board or make a cut in the ground to try to keep noise with in "audio ground". There will be big currents from the bypass caps to the ground pins on the IC. Also: there should be a LC filter on the output of the amp. Watch ground currents in that area.

 

[Mikebits]

Thanks Ron, good suggestions.

 

[ronsimpson]

There is a demo board for the demo board for the audio IC. Look at the layout! (in the manual)

 

[Mikebits]

That demo board provides me some useful info, thanks. I noticed on the demo board that they are driving the PA in single ended mode. In the data sheet they recommended differential input, so I was going to do that, but after seeing the eval board in single ended. Hmm

 

[AnalogKid]

For only one watt, why risk the noise pollution of class D? Lotsa small BTL amps that will make 1 W out of 5 V.

ak

 

[Mikebits]

Well, I am only running 3.3v, but I suppose I could add a 3.3 - 5v converter if the noise is that big of a problem. I have never used the D amps before.

 

[AnalogKid]

Well, I am only running 3.3v, but I suppose I could add a 3.3 - 5v converter if the noise is that big of a problem. I have never used the D amps before.

No need. That particular device has a boost converter built-in.

ak

 

[ronsimpson]

I agree with Analog. One switcher is as bad as another.
Use a ground plane. Make the board a little larger. Look for where the current is flowing. Keep the input and output sections away from each other.

 

[Mikebits]

No need. That particular device has a boost converter built-in.

ak

I think you misunderstood me. I chose the class D part because I am running 3.3v, and I could not find a BTL that could provide the audio output I need at 3.3v. So I was saying if I use a BTL device, I could add a 5v converter, but Ron brings up a good point, adding more noise again. Thanks