circuit layout with charge pump best practices

[jessenator]

Basically what the title says. It seems like dark arts / randomness in the boards I've done in the past.

I know it can't be avoided in some circutstances, but I'm wondering what sort of layout considerations I should …consider.

Here's what I'm working on currently. It's verified on breadboard & (patched) previous version PCB, but I had concerns about the noise. If it's a noisy circuit, so be it, but I'd like to simply learn to lay things out optimally with charge pumps. Is it physical proximity? grounding? For reference I am using the TC7660H. It's not squeal like I've experienced in the past. I don't get anything on a (granted, amateur hour) klone PCB layout of mine either, but apples and oranges and all that. Most circuits I've done don't use a pump, so I don't think about it often.

I simply need -9V for the OTA, speaking of which: I have the unused OTA terminated based on the TI guidelines for op-amps with a bi-polar supply:

I know there are some weird things happening on the surface here, but it's for me to mentally check against a previous schematic built around a single OTA, CA3080 (the big numbers).

Anyhow, some advice/insight would be appreciated. Thanks.

 

[jessenator]

Maybe I should've put this in the PCB design forum…

If this is energy or just not a big deal, then please tell me. My Swiss cheese knowledge of these kinds of things—or just circuit layout in general— brings out the inner worry wart.

 

[jwin615]

I have no idea what I'm talking about in this regard.
but one observation:
If I was worried about noise from one potion of a circuit, I maybe wouldn't put 2/3 of my amplifiers next to it¿
I suspect there may be a trace running under adjacent to the 7660. May have to sacrifice some symmetry(nice job btw)
Re-refrence first sentence.

 

[jessenator]

I maybe wouldn't put 2/3 of my amplifiers next to it¿

This is just now soaking in… here's hoping this board isn't overly noisy. If it needs another revision, I'll definitely move those BJTs further away. See if I can't reorient the charge pump maybe

 

[szukalski]

I'm not an electrical engineer (EE), but the guidance I found was to keep power separate from audio, especially where charge pumps are involved. Similar with signal generation (ie. LFO).
How relevant it is, well that's a different story.

 

[finebyfine]

Do lower switching charge pumps cause the same type/amount of noise? I agree with what’s been said already otherwise

 

[jessenator]

Do lower switching charge pumps cause the same type/amount of noise? I agree with what’s been said already otherwise

On the first rev (before the one pictured), i tried a 1044S and 7660H (>100 kHz) and both exhibited similar profiles to my ears— more brown noise but not intense. A non-turboed 1440 was quite audiby, as expected.

I have abysmal house wiring and depending on what's running in the house the noise may be better or worse. Case in point, the breadboard version had similar, if not quite as intense, noise profile. So it might be my amp is just making it worse coupled with bad house wiring

 

[derevaun]

I suppose doing it at the bypass switch could be an option--there's often a bit of unused space down there. Madbean's Road Rage, for example.

 

[jessenator]

Small update on this: got the revised board populated/verified and it was noisy …until I boxed it. So Apparently I've got lots of RF around my house that is now blocked/not getting amplified, BJT placement notwithstanding. Still, might be good practice to keep 'em separated going forward.