Buck converter circuit critique OBSOLETE

Other Hardware General Electronics
1

Hi all,
I am designing my PCB for an arduino nano controlled relay board with button inputs and led indicators. This is for part of my boat automation project. I would appreciate anyone critiquing my designs and giving tips. To start I will upload the power circuit which takes 12V input and converts to 5V for the logic level functions.

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The power will come from a 'house' battery bank which is designed to supply power for all the non-engine loads. This is connected to the 'start' battery bank which supplies the engine through a VSR (voltage sensitive relay). This means that when the house battery is drained below a certain level the VSR detaches it from the start battery to prevent it getting drained and making it impossible to restart the engine. When the engine starts the alternator charges the engine battery first and then supplies the house battery also. Obviously this means that charging currents could be applied to both batteries and so the 12V will potentially be 14 or more at times.

With that in mind is this circuit adequate to supply the nano?

2

What is Q1 for? It serves no purpose I can think of.

The buck converter circuit is straight from the data-sheet, so I guess it's OK. My concern is that DC DC converters are fussy about layout, and as this one is designed for operation at up to 2MHz it will be especially fussy.

Other than that it looks OK to me.

3

does it provide reverse polarity protection?

The other change from the datasheet is the inductor because it is not available in 6.3uH.

I was hoping this would be the easiest part of the circuit. :slight_smile:

4

Here is my layout

1200×800 265 KB

5

Does it provide reverse polarity protection?

Yes, I think it does. I never bother, I use polarity keyed connectors and if I get it wrong, well, I should know better.

I do not have the skills in SMPS design to comment on your layout, sorry. That said, it is general good practice to include a ground plane.

6

I think I will make the bottom of the board ground. I have a few ground connections there currently. I was going to leave the grounds until the end but I suspect it is no harm to make it ground and treat it that way for now.

7

I think I will make the bottom of the board ground.

Everything on the bottom of the board that is not something else should be ground, unless there is a specific reason to not make it ground. KiCad has a fill option for this, I imagine other PCB design tools do as well.

8

For a very high frequency buck converter like this you need to follow the datasheet guidelines
on layout, capacitor and inductor selection to the letter - a 2MHz switcher is well into the territory
where Kirchoff's laws no longer hold and Maxwell's equations are relevant - layout is part of the
circuit, not a detail.

9

Thanks for the responses. Maybe this buck is a bit sensitive. I have posted my complete circuit in a new post with an alternative buck included which seems to be commonly used. I am marking this topic as obsolete.