The USB specification requires 100uF on the USB ports. TI did not write that specification. Trust me. I know.
If you put the CAP after the switch then it tends to pull down the 5V input when you activate the USB power, something about charging that cap. It works better before the switch as it prevents a dip on the 5V rail, which caused issues with the PMIC, power rail going low after power up. I am not going to make any changes to the design. Fell free to convince the Green people to change their design. As to your specific application, I did not design the board for your application. I did however give it to you for free. Feel free to make whatever changes you need for your application and build you own board. I think the statment on the first page of the schematic is self explanatory. Gerald On Sun, Jul 3, 2016 at 7:02 AM, <kzsoltkzs...@gmail.com> wrote: > "And as we also say, use a good power supply." > This was originator of the problem. At first time we try to use medical > approved 4A PWS.But this type has a fast current protection circuit, which > detect 1ms 4A current peek as short circuit. > So our advise is to use middle categhory PWS (we have success with MW > GS15B-1P1J). > > "we have never lost a TPS5217C due to this issue" > This is understandable beacuse average application is one BBB alone. This > require 2A PWS which have no chance to harm TPS in this way. > But in case of our special application more 5VDC powered device work > together. This can be 2 or more BBB and more other device. This is why we > try to use 4A or higher current PWS. This can demage TPS at startup. > > "I am not sure how to prevent caps from needing to be charged" > You dont need it! > First what need to be learn by power rail diesigner is the rule: > capacitive load on output of power regulator is very sensitive area. This > is why power regulator manufacturer (including TI) using pages to explain > its calculation. > Loading reagulator with high/low/good/bad capcitor have diffrent effect to > stabilized power rail. > At first impression 100uF at position C34 is very high for regulator > output (ext PWS). The 22uF with ESR=20mOhm (TI rec.) limit > startup peak to normal value. > Moreover I cant known philosophy of USB host interface designer, why need > 100uF at IN of PDS? All AN of TPS20x1 PDS are recomend 0,1 to 10uF at this > position except "Typical Hot-Plug Implemantation" where 1000uF applied. But > this is not match, beacuse you cannot Hot-Plug USB host interface to BBB > beacuse it is hardwired. > I think it is some missplacing of this capacitor. USB 1.1 require ~100uF > at downsteram port. But this capcitor must be connceted at output of > TPS20x1 not at input of. This provide a soft charge for system power rail. > At input need just <=10uF. > > -- > 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 beagleboard+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/8d85bcfc-4101-4578-8120-e5a7e27e061f%40googlegroups.com > <https://groups.google.com/d/msgid/beagleboard/8d85bcfc-4101-4578-8120-e5a7e27e061f%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- Gerald ger...@beagleboard.org http://beagleboard.org/ gcol...@emprodesign.com -- 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 beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAHK_S%2BdjCjbkoDZLiVGnr%2BLANUm2qLs8ph%3DaYtkb7Hz35OoF1A%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
