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Class D Switching Power Amplifiers and Power D/A conversion

TI TPA3255EVM
TI TPA3255EVM
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Old 16th July 2018, 01:22 PM   #801
tubesguy is offline tubesguy  United States
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Quote:
Originally Posted by dubai2000 View Post
Thanks for the helpful suggestion - found the document in question, but I still have a question or two. I found those empty solder pads for most components needed to implemet PFFB but what about those parts which don't seem to have such a fixed spot (namely C_fb_in and _out and R_fb_gnd)? This is all pretty small below the board so I am a bit at a loss here. Any support will be greatly appreciated - thx in advance.
Was there ever a response to this post? (I haven't found it searching for "pffb") Or has anyone actually done the modification to the EVM and posted pics? My amplifier needs have changed and now one stereo amp will fill the bill. I have the EVM in place, but it wouldn't be DIY without a significant mod that might allow me to destroy the board, right?
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Old 16th July 2018, 03:40 PM   #802
doctormord is offline doctormord  Germany
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The influence of PFFB on the EVM is less than 6dB, which can be seen from the latest documents at TI. With a good design, which the EVM is, there's (to me) no need for PFFB. With cheap inductors and "bad layout" the performance boost is much more present.
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Old 16th July 2018, 05:14 PM   #803
dubai2000 is offline dubai2000  Europe
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Still, it would have been nice if somebody had done this mod and was willing to explain for less informed members.
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Old 16th July 2018, 05:48 PM   #804
DPH is offline DPH  United States
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I'm not at a point yet where I want to implement pffb due to project prioritization, but I'll be happy to document it when I do. My motivation is honestly more the SNR improvement by lowering my too-high of system gain than anything else. Sorry.

From my basic impressions all the pads needed are on the board, albeit you may need to come in with a daughterboard for the input coming off the accessory header (which I plan on doing regardless).
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Old 16th July 2018, 05:55 PM   #805
doctormord is offline doctormord  Germany
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You'll patch it in at the pads for C73/C74/C75/C76 like a T-filter.


The EVMs PFFB is an older approach which (to my knowledge) wasn't stable with all loads. The newer implementation is stable at all time.

Voltwide implemented a minimal PFFB with only one capacitor per channel to tune for best square wave responce without overshoot even when unloaded.

The older SLAA702 isn't available from TI anymore, which was meant for the EVM, attached is a local copy.


Values from PDF:


TI TPA3255EVM-pffb_zobel-png
http://www.diyaudio.com/forums/attac...1&d=1531763562
Attached Images
File Type: png PFFB_Zobel.png (28.6 KB, 158 views)
Attached Files
File Type: pdf slaa702.pdf (567.7 KB, 13 views)

Last edited by doctormord; 16th July 2018 at 06:12 PM.
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Old 16th July 2018, 05:57 PM   #806
doctormord is offline doctormord  Germany
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Quote:
Originally Posted by DPH View Post
From my basic impressions all the pads needed are on the board, albeit you may need to come in with a daughterboard for the input coming off the accessory header (which I plan on doing regardless).

No, the 3251 and 3255 EVM where made for a different implementation, not having the capacitive "T" arrangement. They just use a single cap.
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Old 16th July 2018, 06:03 PM   #807
DPH is offline DPH  United States
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Thanks, Doc!
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Old 17th July 2018, 05:51 PM   #808
tubesguy is offline tubesguy  United States
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Thanks guys
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Old Yesterday, 09:39 AM   #809
dubai2000 is offline dubai2000  Europe
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Thx for the info.
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