@ John:
Thanks for your answer. I measured with a multimeter directly at the BBB. 
The BBB normally even starts with only 4.5V so its definitely something 
wrong with the PMIC. 

@Gerald:
Thank you. The problem is, we are using the BBB in an industrial product 
that has to run 24/7. Replugging the device is therefore no option. 
Powering the BBB with at least 5.1V seems to resolve the problem but I 
wondered if there is a reason for that.



On Thursday, 7 August 2014 02:13:51 UTC+2, Gerald wrote:
>
> Unplug it and plug it back in. It was designed to work that way. Temporary 
> power loss can confuse the PMIC and put it in an bad state.
>
> Gerald
>
>
> On Wed, Aug 6, 2014 at 6:42 PM, William Hermans <[email protected] 
> <javascript:>> wrote:
>
>> John, this happens to me too, but powering via USB. Once in w blue moon, 
>> there seems to be some sort of race condition, or something where the BBB 
>> is not getting enough power.
>>
>> So in order to thwart this I've stopped using shutdown now -r, and 
>> instead use shutdown now -h. Then manually remove / reapply the USB cable.
>>
>>
>> On Wed, Aug 6, 2014 at 3:44 PM, John Syn <[email protected] <javascript:>
>> > wrote:
>>
>>>
>>>  From: Rico <[email protected] <javascript:>>
>>> Reply-To: "[email protected] <javascript:>" <
>>> [email protected] <javascript:>>
>>> Date: Wednesday, August 6, 2014 at 3:34 PM
>>> To: "[email protected] <javascript:>" <[email protected] 
>>> <javascript:>>
>>> Subject: [beagleboard] Re: Beaglebone sometimes doesn't start after a 
>>> power loss
>>>
>>> Sorry to push... Gerald, maybe you have an idea?
>>>
>>>
>>> On Sunday, 3 August 2014 15:28:45 UTC+2, Rico wrote:
>>>>
>>>> Hello,
>>>>
>>>> I've noticed that the beaglebone black sometimes does not startup after 
>>>> a short power loss, even when pressing the power button, it does not start.
>>>>
>>>> To reproduce with a regulated power supply (tested with BBB rev B and 
>>>> C):
>>>>
>>>> 1) Output of power supply 5V
>>>> 2) connect power supply to BBB
>>>> 3) BBB starts up normally
>>>> 4) down-regulate the output slowly
>>>> 5) at 3.5 V, the beaglebone turns off
>>>> 6) go back to 5V
>>>> 7) press the power button, the beaglebone won't startup
>>>> 8) go above 5.1V and press the power button => now the beaglebone starts
>>>>
>>> Are you measuring the voltage at the BBB terminals or are you reading 
>>> the voltage from your power supply? Do you use thin wires to connect from 
>>> your power supply to the BBB? My thinking is there is a voltage drop across 
>>> the wires of 100mV or more. 
>>>
>>> Regards,
>>> John
>>>
>>>
>>>> I've read the datasheet of the PMIC (TPS65217C) but I cannot find out 
>>>> why the BBB starts at 5.1V but not at 5V, has anyone an idea?
>>>>
>>>> Many thanks,
>>>> Rico
>>>>
>>>> -- 
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