> On Dec 15, 2015, at 9:44 PM, Morgan Redfield <[email protected]> wrote: > > 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?
What I’m recommending is to avoid any antenna pickup by the probe. If you are using a regular probe, then you should probably use something like this: http://www.cliftonlaboratories.com/july_2007.htm <http://www.cliftonlaboratories.com/july_2007.htm> Scroll down to about half way "Tektronix P6106 probe with sleeve removed and grounding clip in place.” That is what I mean by keeping the ground line short. To diagnose your problem, you must start with measurements that you can trust. What is the bandwidth of your scope? Regards, John > > Best, > Morgan > > On Tue, Dec 15, 2015 at 9:35 PM, John Syne <[email protected] > <mailto:[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] >> <mailto:[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] >> <mailto:[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] >>> <mailto:[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] >>> <mailto:[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 >>> <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 >>> <https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe>. >>> To unsubscribe from this group and all its topics, send an email to >>> [email protected] >>> <mailto:[email protected]>. >>> 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]>. >>> 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 a topic in the >> Google Groups "BeagleBoard" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe >> <https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe>. >> To unsubscribe from this group and all its topics, send an email to >> [email protected] >> <mailto:[email protected]>. >> 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]>. >> 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 a topic in the Google > Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe > <https://groups.google.com/d/topic/beagleboard/hpHmvGR3cGU/unsubscribe>. > To unsubscribe from this group and all its topics, send an email to > [email protected] > <mailto:[email protected]>. > 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]>. > 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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