Harvey, you raised several very good points. I cannot say I disagree with anything you said.
Regards, John > On Jul 4, 2016, at 3:36 PM, Harvey White <[email protected]> wrote: > > 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 <[email protected]> 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 <[email protected] >>> <mailto:[email protected]>> wrote: >>> Thank you for your feedback. >>> >>> Gerald >>> >>> On Mon, Jul 4, 2016 at 3:18 PM, <[email protected] >>> <mailto:[email protected]>> 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 >>> [email protected]<mailto:[email protected]>. >>> 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 >>> >>> [email protected] <mailto:[email protected]> >>> http://beagleboard.org/ <http://beagleboard.org/> >>> [email protected] <mailto:[email protected]> >>> >>> >>> -- >>> 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 >>> [email protected]<mailto:[email protected]>. >>> 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 >>> [email protected]<mailto:[email protected]>. >>> 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. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/cjolnb1s1bddugkd1v6c4jeqm1a0mhmvhh%404ax.com. > For more options, visit 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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