| 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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