On Mon, 4 Jul 2016 15:13:00 -0700, you wrote: >Pay no attention to William. You comments are welcome and Gerald has accepted >your comments as valuable input by thanking your for your feedback. Now, let >me address your concerns:
>From my own engineering standpoint (and opinions will, of course, vary): > >1) The power supply used to power the BBB should be selected so that it does >not damage the BBB, so a 2A power supply was specified. If you wish to change >that specification, then the onus is on you to verify that a 4A power supply >will not damage the BBB. Your conclusion that is may damage the BBB means that >you should not use a 4A power supply. In addition, a power supply that is >spec’d at 4A should not shutdown when it sees a 4A load, but rather, it should >current limit at 4A. If the power supply is spec’d at 4A, then 4A should not >be treated as a short circuit. I would have designed the power supply circuitry so that with a power supply of appropriate minimum rating, the maximum rating would not have mattered. Using a power supply with a maximum current rating to avoid damaging circuitry is not (again, IMHO) the best solution. If, because of economic considerations, that decision is made, then it is imperative of the designer to put this information specifically in the power supply recommendations. Not doing this leads to damage, doing this puts the responsibility on the user. Is this a "before the design/after the design"? I don't know, and I don't remember (either way) if this warning was ever in the power supply requirements. Hindsight is 20/20, of course. If it's that important, then perhaps the documentation needs to be changed. Decision not up to me. >2) The TI spec for the TPS65217C is a general recommendation as they are >unaware of how you are going to use the part. The BBB SYS_5V powers several >subsystems, including HDMI, I/O (VDD_3V3B) and USB. Clearly you could move the >100uF to the other side of the TPS2051, but then you need an additional >capacitor on the SYS_5V which increases the cost and doesn’t provide any clear >benefit, if you choose the correct power supply. "correct power supply" bothers me. I'm familiar with minimum current capacity, voltage limits, short circuit current limits (infrequently applied). Again, "a 4 amp power supply will allow the board to damage itself, so we depend on a 2 amp maximum supply to avoid damage." This could be discussed a bit.... >3) As Gerald has pointed out, the BBB is just a reference design. It was >designed as a low cost solution which meant that tradeoffs were required to >keep the price low. Clearly things could have been done differently, but then >the BBB price would have been much higher and the board larger. Given that >most users would probably not need these extra features, they were not >incorporated into the current design. There are several spinoffs of the BBB, >some with wifi, some with more RAM, etc, but none have been as successful as >the BBB. Hmmm, well, perhaps (although not required) it might be nice to know what the engineering limitations are of the design. I've seen 1) the ones I know about, and 2) the ones I haven't found out yet... and 3) the ones people are going to have to tell me about... and I do like paranoid designs..... Harvey >4) While I have provided Gerald input into both the BBB and BeagleBoard-x15 >designs, I ultimately defer to his judgement because he has the track record >or having designed several products that are very successful. > >From my prospective, the BBB design is good, but your input was none the less >valuable. > >Regards, >John > > > > >> On Jul 4, 2016, at 2:11 PM, William Hermans <yyrk...@gmail.com> wrote: >> >> kzsoltkzsolt, >> >> I would like to point out to you that you're talking to *the* person who >> designed the beaglebones, who also used to work for Texas Instruments at >> some point in his career. Someone who has made his designs free of charge to >> the public, which he has made perfectly clear to you in these post that >> you're free to change and use for your own personal use. >> >> So, telling him things, he probably already knows, in hopes of making >> yourself looks good. Actually make you look like a "know it all". e.g. it >> doesn't make you look good. >> >> SO perhaps you should realize that Gerald is probably well aware of what >> you're trying to discuss here, but is unwilling to change for various >> reasons. Reason, that you, I, or the next person do not need to understand. >> Because we can change to designs to our own liking if we so wish. >> >> On Mon, Jul 4, 2016 at 1:55 PM, Gerald Coley <ger...@beagleboard.org >> <mailto:ger...@beagleboard.org>> wrote: >> Thank you for your feedback. >> >> Gerald >> >> On Mon, Jul 4, 2016 at 3:18 PM, <kzsoltkzs...@gmail.com >> <mailto:kzsoltkzs...@gmail.com>> wrote: >> First of all making changes on design "tomorrow" is irresponsible, so I >> never request it. But good to know where is some "leak" in design. For >> example it is help to make workaround. >> >> "TI did not write that specification" >> No, but use it in all reference design. See TI TPS20x1 PDS application >> information. See for example TPS2051 docu Fig 33. >> >> "If you put the CAP after the switch then ..." >> Then why CAP placed OUT of PDS in all TI application information? >> Because PDS has soft start feature which prevent overload IN (BBB SYS power >> rail). See for example TPS2051 docu Fig 4 and 8. >> Fig 8 is perfect draw for this. The soft start feature limit charge of 100uF >> to 0,5A, therefore current never exceed USB1 and 2 current limit, therefore >> no dip on IN. >> This is one main function of PDS. >> >> "I did not design the board for your application" >> It is not required. But during research work to specify our problem I found >> many topic where users discover mysterious problems with power supply, and >> try to found a right one for BBB. This can be originated from startup >> current peak. >> >> >> -- >> For more options, visit http://beagleboard.org/discuss >> <http://beagleboard.org/discuss> >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to beagleboard+unsubscr...@googlegroups.com >> <mailto:beagleboard+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/b974f98a-0cff-4380-af1f-9ce5db9e199f%40googlegroups.com >> >> <https://groups.google.com/d/msgid/beagleboard/b974f98a-0cff-4380-af1f-9ce5db9e199f%40googlegroups.com?utm_medium=email&utm_source=footer>. >> >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. >> >> >> >> -- >> Gerald >> >> ger...@beagleboard.org <mailto:ger...@beagleboard.org> >> http://beagleboard.org/ <http://beagleboard.org/> >> gcol...@emprodesign.com <mailto:gcol...@emprodesign.com> >> >> >> -- >> For more options, visit http://beagleboard.org/discuss >> <http://beagleboard.org/discuss> >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to beagleboard+unsubscr...@googlegroups.com >> <mailto:beagleboard+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/CAHK_S%2BcAH_U%3DVtJmLq62wrVPmRg8%2Bn27YjWM_oeorZezSTKorQ%40mail.gmail.com >> >> <https://groups.google.com/d/msgid/beagleboard/CAHK_S%2BcAH_U%3DVtJmLq62wrVPmRg8%2Bn27YjWM_oeorZezSTKorQ%40mail.gmail.com?utm_medium=email&utm_source=footer>. >> >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. >> >> >> -- >> For more options, visit http://beagleboard.org/discuss >> <http://beagleboard.org/discuss> >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to beagleboard+unsubscr...@googlegroups.com >> <mailto:beagleboard+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/CALHSORo-TL2x_vUEni%2B-daiSEQXxLUU_N5p%2BEh%2Bt6tzpuuPT0g%40mail.gmail.com >> >> <https://groups.google.com/d/msgid/beagleboard/CALHSORo-TL2x_vUEni%2B-daiSEQXxLUU_N5p%2BEh%2Bt6tzpuuPT0g%40mail.gmail.com?utm_medium=email&utm_source=footer>. >> For more options, visit https://groups.google.com/d/optout >> <https://groups.google.com/d/optout>. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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