On Mon, 4 Jul 2016 15:46:43 -0700, you wrote: >Harvey, you raised several very good points. I cannot say I disagree with >anything you said.
Thank you. I prefer paranoid designs myself. However, I don't design commercial products, I design stuff for myself. It does make a difference. If I get it wrong, I have to fix it... and I have LOTS of stuff to fix myself. I also don't have to design to a price point, at least, not as much as for a commercial product. Harvey > >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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