Bipolar supply doubler PCB. Ground plane?

[nonost]

Hi. I'm making a PCB for a bipolar power supply doubler. It gets 9v and gives +18v & -18v. (well, a bit less, but it's ok). Here:



When using veroboards, I tie all grounds from that circuit to pin3 and then it goes directly to the DC jack. Now with the PCB I don't know what to do regarding ground planes. There's an overdrive also in the same PCB, and I'm using a ground plane. Should I isolate the power switching from the ground plane? Or it's ok for the charge pump to be surrounded by a ground plane that doesn't belong to it?

Cheers!

[antonis]

ΙΜΗΟ, it should be better for ALL GNDs (pin3, 100μFs & Diode) to be wired directly to PS GND..

[nonost]

Hi Antonis!

IDK, things might end up a bit too complicated...

I found this:



It's for the MAX660. It's not exactly the same as the LT1054 or 7660S, but pretty close.

What do you think about the ground plane around the charge pump? I can't find anything.

Cheers!

[antonis]

Better look at:
https://www.ti.com/lit/ds/symlink/lt1054.pdf?ts=1683618990175&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLT1054 
(page 24)

[MrStab]

You can place a gap between the portion of the ground plane underneath the charge pump and the rest of the plane, so that they only meet at the PSU ground connection. I wouldn't allow power management ground connections to share the same route back to PSU as audio circuitry, generally.

[nonost]

Hi MrStab. Do you mean a different GND plane for the charge pump? A small one isolated from the main ground plane. Since in the datasheets GND planes are not named, I thought about surrounding it with a keepout area and make the GND connections inside it as needed, and then run a trace to a pad (which I'll run a wire to the DC jack).

Thanks Antonis. I forgot about the TI datasheet.

[MrStab]

I think we're on the same page, Nono. Power and audio in their own neighbourhoods, which meet at the highway.

[ElectricDruid]

I think we're on the same page, Nono. Power and audio in their own neighbourhoods, which meet at the highway.

...and the highway should be as far out of town as possible!

[MrStab]

Further to that analogy: make sure you don't get pulled over without a license! 9KHz is the speed limit!

(The internal oscillators in these charge pump ICs push pedals over the 9KHz threshold of being classed as "unintentional radiators" by the FCC, though not an issue for hobbyists. All the best jokes need explanations.)

[Rob Strand]

It's for the MAX660. It's not exactly the same as the LT1054 or 7660S, but pretty close.

What do you think about the ground plane around the charge pump? I can't find anything.

To me that layout looks good.  It's not about ground planes it's about keeping all current pulses to/from the input and output caps contained around the chip and on their own tracks.

You don't want any of those current paths going to a ground plane as it will "infect" the ground plane with noise from the current pulses.

What you want to do is leave that layout as is and take a single track from pin 3 to the ground plane.  There's not much else you can do with a single power supply with a single ended audio system like a pedal. [Ideally that point is where the power comes in, not at some random point on the ground plane.]

If you want you could increase the tracks in that layout to be larger but it's probably not going to improve things.   It's also OK to surround that chip with a ground plane but you still only want a single ground connection at pin 3 to the ground plane.  Avoid multiple ground connections from the converter to the ground plane.

[nonost]

haha! Didn't know about that MrStab, even the 7660 goes beyond that. All pedals with charge pumps are unintentional radiators 

It's not for commercial use, so no problem

Thanks Rob! Ok. I'm using 15.75 millis(0.4mm) as base width for traces. For power & gnd traces I'm using 33.46 millis(0.850mm).

Cheers!