A couple of my BBBs have begun to not respond or intermittently not respond to the 5V supply, i.e. VDD_5V, but still are able to be powered through the USB. When in this state the board does not appear to respond at all to 5V power, no power or status LEDs. When I first noticed the problem I found that they would eventually return to normal operation if all power was removed for an undetermined period of time.
These devices are setup as remote systems that power up periodically via an external RTC, which momentarily pulls PWR_BUT to ground in order to turn the device on. They are powered through VDD_5V via a custom cape, as such, the error I’m seeing effectively breaks the function of my device.
I don’t know what’s causing this error, but assume that it’s something related to the PMIC. I believe I’ve only seen this issue on RevB BBB’s but the PMIC is the same for both the RevB and RevA boards that I have. I’ve also seen various levels of current draw from VDD_5V when in this state, ~18.5mA in one case and ~0.39mA another time. I was wondering if the PMIC might be in some lockout mode, I know there is an “Under Voltage Lockout” mode. However, I haven’t figured out a good way to test this.
Any suggestions to help debug this issue would be greatly appreciated.
Any chance you can give some more information, like the revision of the board and details on the power supply?
Sorry for the delay in replying.
I’ve only seen the problem start when using my custom cape, which has the following voltage supply:
linear regulator: LT1529-5, capable of supplying 3A of output current.
After noticing the failure to power up, I’ve removed the cape and attempted to power it using a 5V AC to DC adapter capable of supplying 2A. This also doesn’t work after entering this state. I will try another supply but I doubt it will make any difference.
I’ve only seen this on issue on revision 000B beagle bone blacks. I have several A6’s and A6A’s that are not exhibiting this behavior, although I also swapped regulators (originally using LM1086, 5V, 1.5A) upon switching to the 000Bs so this is a bad comparison. I will swap the regulators and let them run for a while to see if this is a likely source of my problem.
This problem sounds similar to that described in the following post ( https://groups.google.com/d/msg/beagleboard/p0CwsGzNYNw/6Ig85JJJviEJ ). However, James noticed the problem occurred when cycling the power, suggesting that it was caused by a brownout. I’m not removing power at all but can still enter a similar state. My only thought now is that maybe when the regulator is entering a low quiescent state that it is somehow triggering a brownout…? It isn’t occurring consistently so it’s difficult to catch this behavior on an oscilloscope but I will try to capture it.
Any other suggestions of things to look into would be greatly appreciated.