Single fault testing TNY280

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Hi! We have a design around the TNY280 which is principle looks like the one in your dataheet.

Now, during CB certification the test house introduced a short between pins D and EN/UV (motivated by the citation below), this caused the optocoupler to blow up which in turn violated the required creepage between the primary and secondary side.

Is there any relevant documentation that we can provide which shows that an internal short between pins D and EN/UV is unlikely to occur?

Best regards

Hi Torgny,
D to EN/UV pins has a very far distance from each other. There's even BP/M in between them. The usual and realistic testing that I've known was that pins next to each other is shorted. I cannot imagine how D to EN/UV will get shorted unless it was intentionally done through wire shorting but almost impossible to happen in the power supply level.

For single faulting testing of the device, we usually do external open or short of the pins. There's no access in the internal circuit of the IC to short it unless the packing is intentionally opened, which will not happen since it will be already a defect part and won't be ship to customer for use in power supply....

Regards,
Jedidiah

Hi Jedidah,
The short is intentionally introduced during CB Safety certification. Motivated by requirements in safety standards. Posting the snip from standard did not work but I'll make a new try, uploading a picture. The test house require some "proof" that it cannot happen. Clearance between pins on the outside is sufficient according standard but can you present some proof that is can not happen internally? Like minimum separation internally?

Regards,

Hi Torgny,

IC's internal distance was not constructed to satisfy the required spacing between D and EN/UV pins. IC will just be a defective device if internal connection is shorted. As such, defective devices (detected thru screening during production) will not be shipped for use in the field.

We would like also to suggest to add zener diodes on those pins or a suitable protective device in a circuit to prevent the blow up issue. This is typical action that we observed from power supply manufacturers to protect their product design from safety failure.

I hope that helps.

Regards,
Kazuya