TPS566231: TPS566231RQFR VIN short to GND immediately upon first power up

Hello,

Few questions regarding this:

• Have you checked for any soldering shorts?
• This may can be due to ESD damage, this may be something to check for
• After second power up, does it operate normally?
• Have you inspected the IC to see any damage done?
• What is the failure rate?
• Swapping for a fresh IC solves the issue?
• Ensure you are following the recommended schematic and layout guidelines from the datasheet, this is very critical

Thanks,

Calan

Hi Calan,
Yes- we have checked for soldering shorts between VIN and GND and do not see them. 
We have not checked for ESD damage, but this happens on new out of the box assembled boards that are handled with ESD precautions when we get them and test them.
The short is present when we stop powering the board and when we remove the chip from the board (we can see the internal short in the chip after depopulating).
On a non current limited power supply, we see the chip smoke and heat damage. On a current limited power supply, there is no visible damage to the chip, or minimal discoloration. 
As I mentioned, we see this in about 10% of our boards.
Swapping for a fresh IC has solved the issue in all cases.
We are following the schematic from Webench and the layout guidelines but are happy to provide Gerber files for your review.
Thanks,
Anushka

Hi Anushka,

I am working on this and will respond to you between this week and early next week.

Thank you,

Calan

Hi Anushka,

I have not seen an issue similar to this with this device. There could be an issue with the board as well. Have you tried a fresh board to see if the first board causes the issue? Please try a fresh board to see if the issue persists in this board or only on the previous one.

Please provide schematic and layout

Thanks,

Calan

Hi Calan,
We have tried a fresh board, this actually only happens with fresh boards (as in, it only happens the first time we power up a board). We've powered on about 40 boards and seen it on 4 (hence the 10% failure rate I mentioned). 
Can I email you the schematic and layout rather than posting on the thread? Please provide a support email I can use. 
Thanks,
Anushka

Hey Anushka,

Thanks for your reply. Sure, I am working on this and will respond to you next week.

Thank you,

Calan

Hi Anushka,

I sent you a friend request on E2E. Please accept this, and we can Direct Message and you can share the schematic and layout.

Please let me know when you have accepted.

Thank you,

Calan

Thanks so much! I just direct messaged you the design and accepted the request.

Hi Anushka,

Thank you, I will review the schem and layout soon, thanks for your patience as I have heavy customer support at the moment.

Thank you,

Calan

Hi Calan,
We just found cold solder on another component on one of the boards. Could cold solder or open connections on any pin possibly cause this? 

Hi Anushka,

Was this component with the solder remnant one of the TPS566231? Yes, any excess solder on the board could be causing the damage/shorting when you power up the boards/device. Please ensure the soldering is accurate and check for any solder that should not be there. Please check the pins of the IC and any components around it. Shorting of nearby devices or connections can also cause damage to the TPS566231. Can you test the boards with the solder issue and also test the boards without the solder issue and compare? Please let me know which ones get damaged.

Thank you,

Calan

Hi Calan,
No, as I mentioned there's no excess solder or shorting on the components. We saw cold solder (a high resistance or open joint between the chip and board, opposite of a short) on another chip (not the TPS566231). We have not identified cold solder on the TPS566231, but we're wondering if that could have caused the issue on any of the boards we previously tested. Could a high impedance between the pin on the IC and the PCB have caused a short on the TPS566231? 

Hi Anushka,

There is a possibility, but it is not one of the likeliest scenarios, I will come back to this theory.

More of a possibility: I noticed in the schematic there is not a resistor divider on EN pin. I see it is connected straight to VIN. There should be a resistor divider on EN to keep the EN voltage within its thresholds. Vin voltage is likely too high for EN which can certainly cause damage. Can you please add the proper resistor divider from EN to Vin to keep EN voltage below 6V? Can you try this and test the board to see if this fixes the issue.

I also have additional theories, please try this first and let me know. 

Thank you!

Calan

Hi, that's a great find, thank you! We will definitely add that. The issue is it's a bit difficult to reproduce the issue on demand, since it only happens to around 10% of boards.
We'd love to hear your other theories as well so we can implement then and see if it makes a difference to our yield. 

Hi Anushka,

Sure, I will provide you with some more information soon, please allow me few days.

Thank you,

Calan

Hi Anushka,

A few more theories I have:

You can double check the VIN to GND resistance on the IC by itself first to make sure it looks ok, then you can check it on the board once it is soldered on and see if the resistance is still the same etc. Then you can check it when no other components are connected around it and see if the resistance is ok still. This will help confirm that the short is happening on the board once it is soldered. Check the value of the impedance on the IC VIN GND pins when it is not on the board versus when it is on the board with no components around it affecting it. The values should be similar. In summary, try to isolate the IC from other components surrounding it and see if the issue can be reproduced. First I would try to add EN resistor divider to VIN and see if this fixes it, then continue to debug with the other methods if not.

Hope this helps. Please let me know results.

Thank you,

Calan