Short circuit power input

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jcribeiro82
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Short circuit power input

Unread post by jcribeiro82 » Thu Jan 10, 2019 2:39 am

Hello,

We have a lot of C2 boards that are failling.
When they fail, all boards have their 5V and 3.3V power input short to GND.

We are powering them by the 5V pins directly (using a very stable DC power source).
Why do you think this is happening?
Can you help us?

Best regards,

José

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Re: Short circuit power input

Unread post by odroid » Thu Jan 10, 2019 10:15 am

We've been shipping over 5~6K of C2 boards every month and we could see 2~4 defectives per month.
So C2 defective rate must be lower than 0.1% these days.

If 3.3V and 5V rails shorted to GND, some ICs on the board could be damaged by unknown electrical shocks.

Can you tell me more about your power supply connection?
Do you mean you connected a power source to 5V rail on 40pin header?

Which USB devices do you connect to C2?
Some self-powered USB devices might cause a voltage conflict and it could damage some C2 boards probably.

jcribeiro82
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Re: Short circuit power input

Unread post by jcribeiro82 » Thu Jan 10, 2019 7:40 pm

Hello,

Thank you for your reply.

Yes. The power source is connected to 5V rail on 40pin header.

We only have a self powered USB device and a bus power audio USB device, so I think it won't be a problem...

We are getting 3.3V from the board to supply our own board.
Do you think that some current spike on 3.3V can be damaging the board and then both 5V and 3.3V become shorted to GND?
Does it make sense? Both rails?

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Re: Short circuit power input

Unread post by rooted » Thu Jan 10, 2019 7:45 pm

Yes, there is no protection on the 5v rail.

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Re: Short circuit power input

Unread post by jcribeiro82 » Thu Jan 10, 2019 8:39 pm

So, do you think we can solve that by changing the power source to J8 (to include NCP IC protection) ?

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Re: Short circuit power input

Unread post by odroid » Fri Jan 11, 2019 9:26 am

Power sourcing to J8 is much better than 40 pin header.
It will not bypass the protection IC NCP372.

But I still have a doubt about 3.3Volt rail.
What is the maximum/peak current of your add-on board?

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Re: Short circuit power input

Unread post by jcribeiro82 » Fri Jan 11, 2019 8:43 pm

Thank you for your reply.

3.3V it's only used for signal conditioning... Total current can be few mA...
About the audio USB, it happens with our without it, so that's not the problem.

I made a test by powering it up a damaged one and no IC is heating. I will try again with higher current...
Can it be a mechanical problem? Can layers be broken and make a hard short internally?

Or do you think some bend on the PCB is causing SPARKGAP to short?
I think you should replace these for TVS diodes in future revisions/boards.

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Re: Short circuit power input

Unread post by jcribeiro82 » Sat Jan 12, 2019 3:43 am

I did 2 more tests:

1) High force applied to the PCB 40-pin connector causing it to bend

Test result: Everything OK

2) High voltage spike on 5V rail

Test result: Damaged board. 5V is now short with GND, but 3.3V rail is not

So I didn't quite reproduce the problem, but the second test result is near...

I would say that it is an electrical problem.
We will start powering it from J8 and add a TVS diode and we hope it solves the problem completely.

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Re: Short circuit power input

Unread post by rooted » Sat Jan 12, 2019 6:13 am

What are you using the devices for if you don't mind me asking?

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Re: Short circuit power input

Unread post by jcribeiro82 » Wed Jan 16, 2019 7:03 pm

We are using it for digital signage.

Do you have any idea about the 3.3V rail short?

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Re: Short circuit power input

Unread post by odroid » Thu Jan 17, 2019 10:47 am

There are a few regulators on 3.3Volt rail.
Refer to page 9 on schematics.
https://dn.odroid.com/S905/Schematic/od ... 171114.pdf
But it is not easy to know which regulator could be damaged by voltage spike.

I hope powering to J8 with TVSD will resolve your issue.

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