Electronics > Projects, Designs, and Technical Stuff

SOLVED: My first TPS61175 Design... no gain...

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SiliconWizard:

--- Quote from: NivagSwerdna on June 10, 2019, 09:24:46 pm ---I have a 300 Ohm resistor across the output.  It's meant to get to 35V... so it should really be trying harder.

--- End quote ---

Alright. Then conversely, you could try with a much lighter load (if you haven't already) and see if it wants to start. If so, the inductor could also be the culprit (getting into saturation)


--- Quote from: NivagSwerdna on June 10, 2019, 09:24:46 pm ---I'm hoping adding a strategically placed 4.7uF ceramic will change the game... should arrive tomorrow.

--- End quote ---

I would expect excessive noise or ripple because of that, possibly reduced efficiency, but not starting at all? Of course we haven't seen your actual implementation so maybe it's a real mess... What kind of capacitors were you using? Anyway, keep us posted. But consider the inductor as well.


NivagSwerdna:
My Output Caps are currently...  C31 is 10uF EEHZA1H100R, C32   4.7uF   EEEFC1H4R7R

My Inductor is SRR1210A-270M which is interesting as I meant to order SRP6540-270M but I can't see why that would be a problem as my selection seems overrated if anything.

NivagSwerdna:

--- Quote from: thinkfat on June 10, 2019, 09:43:29 pm ---How did you build your prototype, on a perfboard, or a breadboard, or pcb?

--- End quote ---
PCB.  Most of the layout is OK IMHO... For the next revision I will improve some aspects.  I think I am probably close enough to the guidelines that it should work.  I did misinterpret NC as Not Connected but otherwise I was OK.

NivagSwerdna:

--- Quote from: SiliconWizard on June 10, 2019, 11:44:08 pm ---I would expect excessive noise or ripple because of that, possibly reduced efficiency, but not starting at all?
--- End quote ---
Exactly my thoughts.

--- Quote from: SiliconWizard on June 10, 2019, 11:44:08 pm --- Of course we haven't seen your actual implementation so maybe it's a real mess...
--- End quote ---
Hard to believe  ;)

--- Quote from: SiliconWizard on June 10, 2019, 11:44:08 pm ---What kind of capacitors were you using?
--- End quote ---
Panasonic Cylindrical Polymer Electrolytic (details above)

--- Quote from: SiliconWizard on June 10, 2019, 11:44:08 pm ---But consider the inductor as well.
--- End quote ---
I did desolder and measure the inductance and it came out OK but maybe I should try another at some point.

thinkfat:
What about the inductor, what is the saturation current? Did you account for ripple current when choosing it?

You went for a switching frequency of around 1MHz, I think. If I use the values from your schematic:

Vin=9V, Vout=35V, fsw=1Mhz, L=27µH, VD assumed 0.3V

Using equation (6) from the datasheet I calculate a ripple current of around 0.24A.

EDIT: I just saw that you posted the inductor type above, 4.2A is of course plenty.

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