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DP83867IR bypass caps

I notice that the data sheet and the troubleshooting guide both say you should put .1 uF *and* 1 uF on every single supply pin, but nothing whatever on the 1.8V pins if you're letting the DP83867 generate that internally.  So that's what I did, and my prototype works, but it's an awful mess of caps.  Meanwhile both of TI's sample circuits that I could find (the evaluation module and the dual-port reference design) ignore this and put a single 1000 pF cap on each supply pin (and opinion seems to be split over bypassing the otherwise unconnected 1.8V pins, or sequencing the power supplies even though the data sheet says not to bother if you're not supplying the 1.8V externally, and my board works fine without that).  So ... can I really get away with just one .001 uF cap on each?  Or some other value (that feels low but I'm not an analog guy so I've been blindly sticking .1 uF on everything for years, with no problems).  Also I feel itchy about not bypassing the 1.8V -- I can't see how the need for that would depend on whose LDO we're using.  But again -- duh.  One.  Zero.  Anything else is really none of my business.  Thanks!

  • To be clear: I mean that TI's own designs use a single 1000 pF cap on each power supply pin (not just the 1.8V ones -- I see how my post could be read both ways), instead of following the guidelines from the data sheet and troubleshooting guide. Does that mean I can do this too or do you need a doctor's note to get away with it? It seems like a silly amount of caps if you really do two per pin as the data sheet says. Tnx.
  • Hi John,

    The datasheet is the final authority when considering external components for the DP83867. Bypassing the caps for the 1.8V supply, when using the internal LDO, is not necessary.

    To remain compliant with the datasheet, you should use two caps per pin as shown in the datasheet.

    Best Regards,