Thanks John, I hear you on the ceramic capacitors. I'll be switching those out tomorrow. For now I wanted to get an idea of what the power rail looked like with the current setup, so I could see if there was anything else that may obviously be contributing to the burned out BBBs that I have.
I'm not sure I understand what you're saying about the probe though. Are you suggesting to shorten the ground wire coming off the oscope probe itself? When you say to short the ground to the probe tip and place it near the switcher, is this to use the ground wire of the probe as an antenna? Best, Morgan On Tue, Dec 15, 2015 at 9:35 PM, John Syne <[email protected]> wrote: > When measuring with an oscilloscope, keep the probe as short as possible. > For example, short the ground to the probe tip and place the probe near the > switcher. If you still see the switching spikes, then your probe ia too > long. A ground wire of 3 or 4 inches is too long. As I said before, > electrolytic capacitors are no good for switchers because their ESR is way > too high. Ceramic capacitors with a low ESR will clean up your power supply > noise and make a big difference. Even tantalum capacitors are no good for > switchers generally speaking. If you look at most vendor reference designs, > they always use ceramic capacitors. In fact, some switchers won’t work > unless you use ceramic capacitors. > > Regards, > John > > > > > On Dec 15, 2015, at 9:04 PM, Morgan Redfield <[email protected]> wrote: > > Hi everyone, > > I probed the 5V line of my setup today, with and without a BBB attached to > my cape. > > With no BBB attached, the unloaded startup looks like this: > <BenchSupplyUnloadedStartup.bmp> > There's considerable noise here, but it doesn't seem to exceed the limits > of the TPS65217. > > > When the BBB is connected to the cape, startup looks like this: > <WallWartLoadedStartup.bmp> > > > So I don't think the issue is with startup transients. > > During normal operation, the 5V rails looks like this: > <LoadedNoise.bmp> > There are 200mV spikes at 150kHz due to the switcher. I haven't seen those > spikes much larger than 200mV, but if they were then I could see them > damaging the TPS65217. > > The capacitors I've been using on my power supply are electrolytic. I can > add some ceramic capacitors as well. > > Does this all make sense? Any other ideas for what may have happened to my > BBBs? > > Thanks, > Morgan > > On Mon, Dec 14, 2015 at 8:44 PM, John Syne <[email protected]> wrote: > >> What is the part number for C2/C13? I would recommend ceramic with a low >> ESR. Tantalum for Electrolytic will have a higher ESR and will not be >> suitable as you will see considerable ripple/spikes. Regarding the relays, >> without the diodes, it will only affect the transistors and not the power >> supply. You want a diode across the relay to prevent the transistor >> collector voltage from rising above the relay supply voltage. When the >> relay switches off, the reverse EMF will cause the voltage on the >> transistor to exceed the relay supply voltage and potentially damage the >> transistor. With the diode, the energy from the reverse EMF will be dumped >> into the relay supply. If you have low EMF ceramic capacitors across the >> relay supply, the supply will remain clean. >> >> Regards, >> John >> >> >> >> >> On Dec 14, 2015, at 4:57 PM, Morgan Redfield <[email protected]> wrote: >> >> Thanks for the advice, guys. >> >> I actually had a couple of relays attached to this without flyback >> diodes, so that may be causing voltage spikes on the 5V input line. >> >> I'll take a look at the un-loaded startup of my regulator tomorrow and >> see how it looks. >> >> The regulator portion of the schematic is: >> <image.png> >> >> Best, >> Morgan >> >> On Fri, Dec 11, 2015 at 9:15 PM, Graham <[email protected]> wrote: >> >>> Morgan: >>> >>> It is likely a transient voltage spike that can come out of your >>> switcher. >>> >>> The BBB does not turn on it's power supply until it thinks the incoming >>> voltage is stable, which means that your 12V to 5V switcher is starting up >>> without a load. If it overshoots badly in that start-up period, it could >>> kill something. Or if it overshoots when the BBB load is finally applied >>> >>> I would start by repetitively starting up your 12V to 5V switcher, >>> without a load on it, and watching what the output does on a storage >>> (memory) oscilloscope, so that you can see the worst case startup >>> condition. Then repetitively add a load equal to the BBB and all its input >>> capacitance, and watch what happens. >>> >>> What were you controlling with the BBB/Cape? Things like relays or >>> stepper motors generate inductive spikes that can easily kill >>> semiconductors, if the spikes are not managed correctly. >>> >>> --- Graham >>> >>> == >>> >>> >>> On Friday, December 11, 2015 at 7:14:38 PM UTC-6, Morgan Redfield wrote: >>>> >>>> I think I managed to burn out the TPS65217 on the BBB using a custom >>>> cape that I designed. The cape has a DCDC switching regulator that I'm >>>> using to drop a 12V supply down to 5V for the beagle bone. I have the 5V >>>> from that switching regulator connected to pins P9.6 and P9.5. >>>> >>>> I've now had two BBBs fail while powering them from the board. I left >>>> both on for a couple of days, and at some point the BBB just died. After >>>> that, the BBB don't boot at all, even with the cape unplugged. >>>> >>>> When I apply 5V from a benchtop supply to P9.6, I only see 1.1V on P9.7 >>>> (system 5V). >>>> If I hit the power button (S3), then the voltage on P9.7 will jump up >>>> to around 2.5V before falling back to 1.1V over around 20s. >>>> >>>> I'm not sure what's going on here, since the power supply I'm using >>>> looks pretty clean to me. It's an average of 5.14V with max 150mVpp noise. >>>> It's rated to 2A current draw. Switching frequency is 150kHz. >>>> >>>> Does anyone have any idea what might be happening here? Any ideas about >>>> what I should try next? >>>> >>>> Thanks, >>>> Morgan >>>> >>> >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to a topic in the >>> Google Groups "BeagleBoard" group. >>> To unsubscribe from this topic, visit >>> https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe. >>> To unsubscribe from this group and all its topics, send an email to >>> [email protected]. >>> 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. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> 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 a topic in the >> Google Groups "BeagleBoard" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> [email protected]. >> 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. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > 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 a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > 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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