Voltage regulation circuit 12V to 5V in 5A range

[Demon]

ARGH! Of course it's only now that I notice Webench generated a layout specifically for that schematic.




I couldn't find any mention of copper thickness in the datasheet. No mention in the Evaluation Board for the TPS56637, but it does have a much nicer layout with A LOT MORE cooling holes and a wider area.




I must have read about the copper thickness in the datasheet for another TPS. I just can't remember which cause I looked at so many.


EDIT: No mention of copper in their Quick Reference Guide:

https://www.ti.com/lit/an/slva958b/slva958b.pdf

[Demon]

Bingo, I must have seen this while researching the LM1084. Digikey PDF for the LM76002 on page 43:
https://www.digikey.ca/en/htmldatash.../1/lm76003rnpt

TI recommends using a four-layer board with the copper thickness, for the four layers, starting from the top one, 2 oz / 1 oz / 1 oz / 2 oz.

[Demon]

TI's Eval board for the TPS56637 is 51mm x 64mm. I figure it would be wise for me to use the same dimensions until I have an actual board to check under the infra-red camera.

Increased the amount of cooling VIAs like on the Eval board.

Used a DIP header for the leads for a cleaner look once on the prototype.

Increased thicknesses to 2-1-1-2 ounces and tweaked the trace width/space according to JLCPCB minimum requirements for a 2oz board.




I still have to figure out how I can make my VIAs have large copper rings like the Eval board. I probably have to replace them with actual holes (like I have on the 4 corners - nice visible copper ring).

[Demon]

Had to make the hole a Part, not included in Schematic, BOM or To Be Populated.

Discovered the Create From Selection / Create Array feature; real time saver to make grids of parts.




Starting to look 1/2 decent.

[Ioannis]

Wow! You did a lot of work!

I am pretty sure that the extra layers TI suggest are for less noise ad better heat dissipation. Have you checked how much extra cost is added by JLCPCB?

In general if you want/need to make the board smaller, you can move all componets to the left, connector closer to the inductor and the right board edge also moved to the left. I don't see why this pcb needs to be that large. Saves cost also I guess.

I'd add an extra output capacitor for less noise and better operation without much cost. Parallel capacitors make for lower ESR also.

Nice design. You become an KiCad expert!

Ioannis

[Demon]

EDIT:

At first I was tempted to make 2 prototypes; 2 layers and 4 layers; just to see if the extra cost is worth it. But the more I think about it, the more I'm leaning for the 4-layer design.

Two of the main objectives with this circuit is to reduce heat and stabilize the voltage (ripples). If the pros design their Eval board to that size with 4 layers, I can't really see why I should consider cutting corners.

But boy am I tempted.

[Demon]

...Have you checked how much extra cost is added by JLCPCB? ...

Not yet, I wanted to get as close to a "finalized design" before using JLCPCB's quote generator.

... I'd add an extra output capacitor for less noise and better operation without much cost. Parallel capacitors make for lower ESR also. ...

I didn't know that about the lower ESR.

EDIT the CAPS section

I just noticed the datasheet has a range of output capacitance at 5V from 25 to 100uF (table 4). So I just added 10uF and 1uF ceramics alongside the 47uF.

These guys have a nice bla-bla about "why there can be too much output capacitance on SMPS circuits":
https://www.cui.com/blog/understandi...citance-limits

... Nice design. You become an KiCad expert!

Ioannis

Thanks, but I can't really take credit for the design. I feel like Mr. Bean copying the test answers from the guy next to him. I really did put a lot of effort to do as close to what TI recommends.

As for "Kicad expert", that remains to be seen.

[Demon]

Well, if I'm going to have all that unused real-estate at the top, might as well do something with it:

- DC jack,
- power switch,
- multiple output headers,
- amp and volt test points.

It's all parts I have on hand, so it's not really costing me more. I don't see how it would disturb the cooling, since TI placed all the ventilation holes on the bottom section. It anything, it's extra cooling fins.




Now I just have to remember to slap a jumper on the amp test point for the circuit to work.

[Demon]

... Have you checked how much extra cost is added by JLCPCB? ...

Ioannis

4 layers with 2-1-1-2 ounces with assembly, the area of my circuit jumps from 63mm x 50mm up to 73mm x 70mm.

2oz $32.20
1oz $16.07

Another issue, I can't use Economy with 0201 SMD, i have to use Standard. I had to swap 0201 resistor and capacitor for 0402.


Final bill for 5 PCBs:
- PCB $55.45
- Assembly $83.89
- Total $165.21 (with UPS shipping), $33.04 each PCB.


Plan B:

1oz all layers

PCB $23.15
PCBA $67.92
Ship $ 25.87
Total $116.94, $23.39 each PCB.


Tempted to go with plan B. It's not like I'm going to push 5 amps, most likely 2.5A at best.

[Ioannis]

Ten dollars is quite enough. I'd select that 1oz too.

Maybe and more caps too.

Ioannis