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TPA3255: Cannot get TPA3255 to work. Possible Test Power Supply issue?

Part Number: TPA3255

Dear Forum

I am still battling like the Spartan 300 on this to get this wonderful chip to work 'for me'...   I've discovered some alarming issues that are intuitively suggesting I might have a problem with the test power supply grounding.

1) I've checked my PCB a million times. (no shorts and all connections are DRC checked.   I ensured my schematic of the chip is accurate)

2) I noticed that ONE side of the 3255 came alive and functioned fine.

3) I checked the following pins "AVDD and DVDD"  and found AVDD was occasionally 'there' and then not.  The disturbing thing was, when I moved my finger close to the Reset line (but not touching) it would come ALIVE and be the correct voltage of around 7.5v... move my finger away.. dead.  Other times it's up and down like a yoyo on/off... on.. etc.  I cannot for the life of me see how AVDD would dissappear simply because of some capacitive closeness of my finger to the reset line.  (yes, I've changed the chip a few times to eliminate possibilities)

4)  The only thing I can come up with as to why this very inconsistent and erratic behavior is happening, might be related to my rather long DC power leads. I have 2 supply sources. +/-12 for the low voltage lines (the -12 is for my op amp)  and 31v  for PVDD.

5) I see on the EVM that you have tied both FAULT and CLIP to 3.3v via some resistors. (47k) But I understood from the Data sheet that these are internally tied to a pull up voltage.  Is there a special reason for this connecting to 3.3v outside the chip?

I've got very good ground planes all over the board, so I don't think that's the problem...however the length of lead to my power supply is concerning me at last.

Could some one make an informed comment about whether this kind of erratic behavior could be likely coming from long ground lines to my power supplies?  I can't see much different between my device and the knock off fake TI unit from China (which worked fine).. except that it uses a buck converter close to where the 53v comes in..and obviously, the grounding and supply lines are very tight compared to mine.

Looking for some answers....
Julian

  • Did you have chance to get TI TPA3255 EVM board and run test comparing with your board?

    EVM user guide : www.ti.com/.../slou441.pdf
    quick startup guide: www.ti.com/.../slou458.pdf to double check your setup.

    regards
    Linda
  • Hi Julian,

    What are you using to drive the Reset pin? We also might need to take a look at the board layout and schematic to see what's possibly going on.

    Regards,
    Robert Clifton
  • Hi Rob

    well...I've had some success!   but at a cost.. (in terms of frustration)... These are the painful steps of this 'pilgrim'.

    1) Unstable, erratic...but on ONE board (same as another I've used)... side A and B "worked"...but C&D did not.
    2) Concluding that my long power supply leads were contributing to this situation, I whacked a 220uf decoupling cap on the board at the +12 input point.

    3) Result?  Amazing difference... sort of.. All the voltages and Reset and Fault went to their correct values, but at this point I had NOT connected the output filter to either side, I simply wanted to 'see' if the PWM was occurring.

    4) Installing the filters.... problem!  A&B worked perfectly, but C&D did not... nothing.....and FAULT went low.

    5) I concluded at this point, that though I cannot see any actual board fault... there HAS to be some issue with the C&D side filter parts or their layout which is causing C&D not to work, and Fault to come on.

    6) I then built a 'rats nest' of hard wired parts for the filter off the board, then connected it up.. SUCCESS!... both sides worked.  (conclusion?  See the point 5 above)

    RESET... to answer your question, in this case I am not 'driving' it at all.. I simply assumed the internal pullup would make it do the right thing, and it seems to have done so. I can manually short it out to create a hard reset, but didn't seem to need to.

    AT this point... I'm happy that I have a starting point to implement the  3 X 3255 project that I've been working on for eternity!  This will have 2 x power amps @ 300w  (bi amped, tweeter (A&B) and woofer (C&D) drive) and a foldback amp for stage use.

    This has come about since I wrote my letter begging for help.. so In a sense I will say "situation resolved" until the next hurdle arises.

  • Hi Julian,

    I'm very glad to hear you were able to get this resolved! Let us know if you have any other issues.

    Best Regards,
    Robert Clifton