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] > <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 --- 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.
