3v3 regulator bug: https://groups.google.com/forum/#!msg/beagleboard/7sxPePT7wkM/3vFMPydR20IJ
The issue is the interconnection of the 3v3a and 3v3b power domains, > resulting in significant leakage current between them (e.g. via protection > diodes) whenever one is powered while the other is not. The 3v3b -> 3v3a > leakage was of course exactly the reason for moving the enable-signal of > the 3v3b regulator (U4) from 3v3aux (LDO2) to 3v3a. However, while this > resolved the issue at boot, it did not resolve it at shutdown when running > on dc power, and made it far worse when running on battery. > > The problem is that when the 3v3a supply (LDO4) is disabled, the 3v3b > regulator remains enabled until 3v3a drops below the threshold voltage of > the enable-input of U4, which is far below 3.3V (specified to be somewhere > between 0.4V (at 25 ͏°C) and 2V). As a result, current will start to flow > from 3v3b to 3v3a, and apparently enough current to keep it logic-high in > the opinion of the 3v3b-regulator (despite the ~375 ohm discharge resistor > the PMIC applies when LDO4 is disabled!). > > Thus, once turned on, the 3v3b regulator manages to keep itself enabled > indefinitely as long as it is supplied from SYS_5V. When entering > off-state, the PMIC automatically connects SYS to battery power rather than > DC- or USB-supply. If there's no battery, then the capacitors on SYS will > drain pretty fast hence the 3v3b shutdown is not delayed much. If there's a > battery, then you're pretty screwed. > > It is very important to note that this issue is not merely one of battery > lifetime; this leakage current may *damage the processor*. > > Op woensdag 21 december 2016 13:55:57 UTC+1 schreef Gerald: > > And what is the 3.3V bug? > > Gerald > > > On Wed, Dec 21, 2016 at 6:54 AM, Jason van Belzen <[email protected] > <javascript:>> wrote: > >> Hi, >> We are planning to build an IoT gateway based on a Beagle Bone Black. >> Till now we were experimenting with the Beagle Bone Black Rev C. >> Since we need to protect the filesystem, we want to use a battery so we >> can detect a power failure and nicely shutdown the system. >> >> Unfortunaletly we encountered a problem. >> After shutting down the system with a battery connected, the 3v3 >> regulator bug is triggered. >> The BeagleBone Black is a good board for our purpose, so we really want >> to use this board. >> >> A few questions come up in our minds. >> 1. How bad is this bug? Is it really gonna damage the processor? >> 2. Are there any other solutions than patching to an unified 3v3 rail? >> 3. Are there any next revisions planned for the BeagleBone Black? And if >> they are planned, will this bug be fixed in the next revision? >> >> Thanks. >> >> Regards Jason >> >> -- >> 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] <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/a3dea840-c1cf-4dad-a0dc-b19ba9936504%40googlegroups.com >> >> <https://groups.google.com/d/msgid/beagleboard/a3dea840-c1cf-4dad-a0dc-b19ba9936504%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > Gerald > > [email protected] <javascript:> > http://beagleboard.org/ > [email protected] <javascript:> > > -- 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/bbbedc74-a881-4c4e-84f5-0897b8ea8372%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
