Electronics > Projects, Designs, and Technical Stuff

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

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thinkfat:
BTW I ran your data through TIs power design workbench and while it comes up with pretty much the same values you have in your design, the output cap is suggested as combination of 1 10µF electrolytic and TWO 4.7µF ceramic caps, due to the heavy derating that applies to ceramic caps under DC. Also, Cin is suggested as  THREE 10µF ceramic caps.

NivagSwerdna:

--- Quote from: thinkfat on June 11, 2019, 10:19:52 am ---... TWO 4.7µF ceramic caps, ..., Cin is suggested as  THREE 10µF ceramic caps.
--- End quote ---
That's more than I have... and sounds rather expensive!  The 4.7uF should arrive soon and I'll stack a couple and see if it makes a difference.

SiliconWizard:
That's kind of weird... You could also try and play with the soft-start capacitor's value to see if there is a link with that, also check whether your input voltage source can provide enough current...

I've seen a couple threads about the TPS61175 on TI's forums, but nothing really helpful...

NivagSwerdna:

--- Quote from: SiliconWizard on June 11, 2019, 11:41:39 am ---...also check whether your input voltage source can provide enough current...
--- End quote ---
Currently attached to bench supply with 500mA current limit.  I think the scope pics suggest the supply is holding up.  And I'm feeling the SS is also about right as the blip occurs after most things have stabilised.
If I had to bet... I would say 4.7uF MLCC on the output will fix it.

NivagSwerdna:
Firstly, thank you to those who have kept me company on this thread, particularly Silicon Wizard, it's a lonely business trying to solve something in your little electronics lab when nothing makes sense...

Anyway so I added 4.7uF MLCC to the output side... no change....  added 4.7uF MLCC to input side no change!! Curious!

I looked REALLY hard at the component selection but despite the Vf of my diode being 700mV.... and having doubts... I then decided I must be fundamentally on the right track and there must be a gremlin...

R31 and R34 form the feedback divider...  (Now this is the top layer... so no imaginative silk screen mirroring going on but...) (See PCB Layout below)

Swapped the two components on the board and...

[Spoiler: The R34 label is next to R31 and vice versa, must have got mixed up in layout ]

OMG... two days (on and off )... of my life!   :)



 

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