Ok, I'm tackling the PSU design and here I really feel the IC shortage. I was initially planning on using the LMR16006 as regulators. One for each tpa3255 12V supply and one for the opamps. But it's out of stock for the foreseeable future.
So the only things that seem still widely available at reasonable prices are either the lm2574HV (low switching speed and big package) or the lm5574 (faster, better efficiency, smaller but more passive components required).
I'm leaning towards the lm2574HV... should I avoid it ?
So the only things that seem still widely available at reasonable prices are either the lm2574HV (low switching speed and big package) or the lm5574 (faster, better efficiency, smaller but more passive components required).
I'm leaning towards the lm2574HV... should I avoid it ?
For audio; take anything that has a constant freq above 400kHz or so
Stay very far away from those things that go into burst mode etc
Stay very far away from those things that go into burst mode etc
Ok, so lm5574 it is then.
Btw, reading its datasheet makes me realize that I should really consider how to synchronize not only those three regs but also the tpa3255 themselves. A 4 layers pcb looks more and more appealing.
Btw, reading its datasheet makes me realize that I should really consider how to synchronize not only those three regs but also the tpa3255 themselves. A 4 layers pcb looks more and more appealing.
Why wouldn't you use a 4 layer board????
Standard these days, not much more expensive, makes your life (routing the PCB) an awful lot easier, and the design a lot more robust.
I can't remember the day that I didn't use a 4 layer board for any more serious design.
I often use "4.5" layer boards, using one layer for power supplies, with symmetrical power rails for example.
Don't really see why you would want to sync a bunch of regulators?
Everything above 400kHz can be filtered away very easy.
Last edited:
Certainly 4-layer ease the pcb layout. But -
Handsoldering SMD-parts on 4-layer-pcb is a pain in the xxx.
Been there, done that.
Handsoldering SMD-parts on 4-layer-pcb is a pain in the xxx.
Been there, done that.
I have done it with many PCB's as well, don't really share that pain.
Works totally fine.
Wrt the 2 vs 4 layers. I was looking at the pricing from JLCPCB. As a hobby project, I'd like to keep the cost of the prototypes low but still have usable boards if by chance it worked out at first try.
For 1oz copper boards, 2 vs 4 layers isn't a big difference. It gets more significant once one adds the 2oz external layers. Furthermore, they only offer 0.5oz for the internal layers. So they only can be used for low power stuff, not the power section. 4 layers with all around 2oz or even 1oz internal layers get a lot more expensive in small serie.
So... I was kinda hoping to stay with 2 layers, just like the reference boards. But that was perhaps wishful thinking.
@bucks bunny: the pcb absorbed most of the heat ? Was it due to the large use of ground and power planes ?
For 1oz copper boards, 2 vs 4 layers isn't a big difference. It gets more significant once one adds the 2oz external layers. Furthermore, they only offer 0.5oz for the internal layers. So they only can be used for low power stuff, not the power section. 4 layers with all around 2oz or even 1oz internal layers get a lot more expensive in small serie.
So... I was kinda hoping to stay with 2 layers, just like the reference boards. But that was perhaps wishful thinking.
@bucks bunny: the pcb absorbed most of the heat ? Was it due to the large use of ground and power planes ?
If you have big ground planes, use unleaded solder and/or want to improve quality of solder joints, preheat your board.
At home this could be a aluminium plate with two power resistors on the bottom and an adjustable power supply.
If you have components on the other side too, I used a hairdryer before that I somewhat fixed and directed at the board.
Anything from 40° to 90° will help a lot although the latter you probably only need if using lead-free solders.
There are some lead-free solders with indium that even melt before the leaded ones but those are quite exotic.
At home this could be a aluminium plate with two power resistors on the bottom and an adjustable power supply.
If you have components on the other side too, I used a hairdryer before that I somewhat fixed and directed at the board.
Anything from 40° to 90° will help a lot although the latter you probably only need if using lead-free solders.
There are some lead-free solders with indium that even melt before the leaded ones but those are quite exotic.
I don't know how much you wanna put on the board, but 100x100mm should be big enough.
The difference is 5 euro between 2 and 4 layer for 5 pcs.
There are other places to order PCB's you know 😉
I definitely will never go back to the old 2 layer are anymore.
To much of a compromise in the design and robustness department.
I really had never ever any problems soldering on 4 layer, so I don't understand were that experience is coming from?
btw, if you're really worried about the thickness, just use the top layer for your main supply voltage.
The difference is 5 euro between 2 and 4 layer for 5 pcs.
There are other places to order PCB's you know 😉
I definitely will never go back to the old 2 layer are anymore.
To much of a compromise in the design and robustness department.
I really had never ever any problems soldering on 4 layer, so I don't understand were that experience is coming from?
btw, if you're really worried about the thickness, just use the top layer for your main supply voltage.
Last edited:
Thanks again for the comments. Lots of food for thought.
I at first thought of doing a big pcb with everything on it: linear PSU (which takes a lot of place), regs, input, amp sections, ... It might actually be more cost effective to have three sub pcbs: one for each amp and one for the PSU (which could very easily be 2 layers). It gets even more cost effective if the amp section PCB can be either fitted for stereo BTL and PBTL.
Especially if I mess one thing up...
I at first thought of doing a big pcb with everything on it: linear PSU (which takes a lot of place), regs, input, amp sections, ... It might actually be more cost effective to have three sub pcbs: one for each amp and one for the PSU (which could very easily be 2 layers). It gets even more cost effective if the amp section PCB can be either fitted for stereo BTL and PBTL.
Especially if I mess one thing up...
If it is just for an hobby/side project, go modular.
For some reason all these PCB manufactures have some kind of limit for board smaller than 100x100mm.
If you go even 1mm above, they will cost you a lot more all of a sudden.
If it's for production, modular will be more expensive in the long run.
Although, the prototyping could be still still done modular.
A linear PSU is of course very straight forward.
So in that case I would focus fully on the TPA.
In fact, one could even do all the rest 2 layer and only use 4 layer board for the TPA.
My advise; first lay all the bulk parts out.
Bulk parts are the capacitors, inductors, TPA IC's, connectors and such.
Try to fit that all on the top as neat and tight as possible.
After that, use the bottom layer as just one layer to fill in the rest.
I see to many people going always way to much into the details.
While almost every amplifier needs these (same) bulk parts anyway.
For some reason all these PCB manufactures have some kind of limit for board smaller than 100x100mm.
If you go even 1mm above, they will cost you a lot more all of a sudden.
If it's for production, modular will be more expensive in the long run.
Although, the prototyping could be still still done modular.
A linear PSU is of course very straight forward.
So in that case I would focus fully on the TPA.
In fact, one could even do all the rest 2 layer and only use 4 layer board for the TPA.
My advise; first lay all the bulk parts out.
Bulk parts are the capacitors, inductors, TPA IC's, connectors and such.
Try to fit that all on the top as neat and tight as possible.
After that, use the bottom layer as just one layer to fill in the rest.
I see to many people going always way to much into the details.
While almost every amplifier needs these (same) bulk parts anyway.
Coming back to this... There is a non trivial difference. The GVDD and VDD supplies are rated for 12V nominal, 13.2V max for the normal version. The Q1 version only accepts 10.6V nominal, 11.4 max. The current draw is similar though so the Q1 should run marginally cooler. The max signal input voltage is also the same.
The other differences are in the "Operating junction temperature range"
As well as the ESD voltage.
Very typical for "automotive" parts.
As well as the ESD voltage.
Very typical for "automotive" parts.
After countless permutations, all the "big" parts have found their place on the board. It's 10x10cm for now. Progress is slow, doing this in my free time.
Inductors are ICE 1D23A, filter caps are TDK MKP, the reservoir caps are 22mm 4700uF/63V, nichicon UVR or UFW. The zobel parts will be big smd under the board.
In a "duh" moment, I realized the lm5010 used in the EVM is still available. 🙄 So I'll use it for the 12V line.
Inductors are ICE 1D23A, filter caps are TDK MKP, the reservoir caps are 22mm 4700uF/63V, nichicon UVR or UFW. The zobel parts will be big smd under the board.
In a "duh" moment, I realized the lm5010 used in the EVM is still available. 🙄 So I'll use it for the 12V line.
Attachments
It will probably shrink by a cm or two. I've "only" to fit the opamp stage and the regulators there. For this kind of things, I tend to layout functionnal blocks with ample room and then push them closer together.
Ah yes.
Keep in mind that some THT parts are smaller when it comes down to board real estate 😉
There seems to be a lot of empty space right now.
What I sometimes do is to split up the bulk capacitors into smaller ones.
Which will give a better ESR in general as well.
Just some ideas.
I always like to go for as small as possible, some people don't seem to be bothered to much about it 😀
Keep in mind that some THT parts are smaller when it comes down to board real estate 😉
There seems to be a lot of empty space right now.
What I sometimes do is to split up the bulk capacitors into smaller ones.
Which will give a better ESR in general as well.
Just some ideas.
I always like to go for as small as possible, some people don't seem to be bothered to much about it 😀