TPS54340B: Wont start up with more than 220uF output caps on negative rail. Inverting Buck Boost

Mans Henriksson

Part Number: TPS54340B

I used https://www.ti.com/tool/PMP10090 as reference for a dual rail 12V supply

I added some extra filtering:

The problem is that i wont start when C4 and c14 is populated, i get only short spikes when looking with the oscilloscope, my voltmeter shows 8 to 9 volts (going up and down)

My guess is the softstart, and current inrush to charge the caps, is the problem, but i dont know how to fix it.
I powering it with a 12v 500mA "wallwart"
i actually got it going with my bench supply, giving it some more current and a bit higher voltage, but that's not doable in the real world application of this power supply

over 4 years ago

0 Samuel Jaffe over 4 years ago

TI__Mastermind 25590 points

Mans,

Yes, likely to do with current limit. Please share the scope shots you're referring to.

Thanks,

-Sam

0 Mans Henriksson over 4 years ago in reply to Samuel Jaffe

Prodigy 10 points

zoom in on the up slope:

zoom out:

sorry if these scope shots are a bit lofi

0 Samuel Jaffe over 4 years ago in reply to Mans Henriksson

TI__Mastermind 25590 points

Mans,

Thank you for sharing. Is the input voltage collapsing?

If the wallwart can't support this current you'll need to either:

Choose a higher power wallwart
Increase CIN or decrease COUT
Implement a soft start circuit like this.

-Sam

0 Mans Henriksson over 4 years ago in reply to Samuel Jaffe

Prodigy 10 points

Thx, im gonna start with trying a bigger input cap.
I have not looked att the input side with a scope yet.

0 Mans Henriksson over 4 years ago in reply to Samuel Jaffe

Prodigy 10 points

after a bit more research it might seem its my wallwart was the problem. sry about that!
That said, i think the power should still "boot" even with a 500mA wallwart
gonna research soft start a bit more, but as for now my power supply is running nice with all of the intended caps from a 9V 1.2A wallwart

0 Samuel Jaffe over 4 years ago in reply to Mans Henriksson

TI__Mastermind 25590 points

Mans,

Good to hear! I'll close this ticket. If you have any further questions please start a new ticket and we'll help you out.

Thanks!

-Sam

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TPS54340B: Wont start up with more than 220uF output caps on negative rail. Inverting Buck Boost