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TPA3255-Q1: LC Filter Inductor Saturation

Part Number: TPA3255-Q1
Other Parts Discussed in Thread: TPA3255

Would using a filter inductor that has a saturation current lower than the TPA3255 current limit (R_OCADJ=30.1kOhm, I_OC=13A), such as UA8013-AL (Isat_10% = 12A, Isat_30%=13.2A), cause the inductors to begin to saturate, and consequently pass more switching ripple to output than would be expected if an inductor with a much higher saturation current was used?

  • Hi Evan,

    It actually depends on how much power you are getting from the TPA3255. If it can touch the OC limit in normal working, then a higher saturation current is recommended. If only considered from OC protection perspective, some saturation level when OC happens is fine.

    Thanks!

    Regards,

    Sam

  • Sam,

    Thanks, that was my thought as well. 

    In that case, do you have any other ideas why a post-filter PBTL arrangement with UA8013-AL would be allowing higher 600kHz switching ripple through to output as compared to an equivalent pre-filter PBTL arrangement? Do you spot any obvious issues with the Post-filter PBTL schematic? Perhaps the fact that OUT_A and _B are going thru the same dual inductor (i.e. coupling between the two coils in the same package)? 

    Post-Filter PBTL:

    Pre-Filter PBTL:

    You'll note the pre-filter inductors are 3.3uH instead of 7uH.. this is due to findings of mine from a few years ago:

    https://e2e.ti.com/support/audio-group/audio/f/audio-forum/728481/tpa3255-lc-filter-design-for-pbtl-pre-filter-vs-post-filter 

    Both the schematics above should have the same voltage frequency response. 

    Thanks,
    Evan

  • Hi Evan,

    Well, personally I don't see the reason why there is difference between the Pre- and Post- filter feedback... If you have any idea, please share. Slight smile In my mind, the parallel configuration, either Pre- or Post- filter, just provided doubled current capability, but should not have impact on the frequency response... 

    I would like to do some bench verification and get back to you later. Thanks!

    Regards,

    Sam