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Schematic problem - It gets hot and smells like burning (lemmy.ca)

submitted 2 months ago by [email protected] to c/[email protected]

8 comments fedilink hide all child comments

I've been messing around with circuits my entire life but this design was time sensitive and I've never done my own PCB designs before, so I hired someone to put this together. After getting some test boards, when I plug them in the charger chip gets very hot and smells like burning....

Circuit is just a simple li-ion usb charger and a switch. I've gone through the datasheet for the bq25302 more times than I can count and I'm missing something obvious here. Using it just for delivering power seems to work fine, the problem is only when charging.

I do see R6 + R7 off TS don't have the recommended 10k values, but I don't feel like that would cause what I'm seeing. This is being connected to a 21700 lipo.

Someone mind lending me their eyes please?

bq25302 datasheet - https://www.ti.com/lit/ds/symlink/bq25302.pdf

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[–] [email protected] 4 points 2 months ago (1 children)

I could be wrong, but I did finish a degree in EE even if I just do software now. But here's my quick take on it.

Probably because you're driving voltage on STAT from REGN.

STAT should have a current limiting resistor on it, go through your led, then ground.

REGN should have a 2.2uf cap between the pin and ground according to the datasheet.

[–] [email protected] 2 points 2 months ago

STAT should have a current limiting resistor on it, go through your led, then ground.

That would make sense, but page 21 of the datasheet with a typical application shows it going to REGN.

If it's missing the cap on REGN though, that would probably fuck this all up? I must admit I'm not good at understanding when/where caps are applied.

[–] [email protected] 3 points 2 months ago (1 children)

There should be a capacitor between REGN and ground and BAT and ground.

[–] [email protected] 1 points 2 months ago (1 children)

Oooh, thanks.

Stupid schematic question for a second, when looking at this:

If the "REGN" above the LED there is just referring to the REGN pin right below, why doesn't the line just go back down to the pin? Is this just a style thing, or does it mean something functionally different?

[–] [email protected] 3 points 2 months ago (1 children)

It means the same thing. I would have just drawn a line since they are right next to each other.

[–] [email protected] 1 points 2 months ago

Thanks!

[–] [email protected] 1 points 2 months ago (1 children)

If you don’t mind me asking: what is this for? Is it a hobby? I have no idea if any of this, just somehow came across your post

[–] [email protected] 1 points 2 months ago

Long term hobby that I'm trying to now turn into a small business / online store.