LNK304 latches OFF due to input surge testing

Hello Robert,

Thank you for your interest in Power Integrations product and sorry for the late reply.

To begin with, can I get more information from you to have a better understanding of the problem.

Firstly, can you attach the schematic, i want to know what's your input stage design and load conidtion. 

When you mention AC surge, how much is your surge level. Is it combination wave surge or ring wave surge.

Do you have any probes connected with the board. 

If you can get waveform about the bus voltage at the input side bulk capacitor, it will be even better for us to understand the issue.

Best regards

I am NOT probing this circuit when the latch-up occurs.  I will try to answer your other questions...but in the meantime, can you tell me what conditions can possibly cause the IC to latch-up, and NOT auto-restart?  Can excessive input voltage cause this latch-up?  That would be the simplest explanation.  Thanks again for your help.

Hello Robert,

Under normal condition, there is no latch up options for the device. standard surge should not cause any latch up issue. So here we need to know how much surge you applied, 1Kv, 2KV or any higher level and the surge type is ring wave or combination wave. In this way, we can estimate how much excessive input voltage the deivce will see.

by the way, can you share your schematic? i want to learn which diode you are using. if the diode is too slow, there will be lots of ringing and it may cause lots of unexpected performance of the IC. please share the schmatic if possible.

if you can plot the waveform during your surge test, it will give us more direct information about the performance, like Vds, input voltage of the bulk capacitor or the BP voltage. 

Best Regards

I can send you parts of my SCHEMATIC, as a WORD DOC.,  but I do not want these on public forum.  How can I send them just to you?

I really do not like this forum approach to applications help.  You are very response, and I appreciate that, I just think this is a terrible way to seek applications assistance.

That said...The rectifiers I am using in 2 places are extremely fast (STTH1R06 = 25nsec).   They are only 600V parts.  If the freewheeling diode avalanches, could that cause latchup?

Thanks again for your continued help.

Bob Buono, Crestron Electronics

Hello Bob,

We understand it is confidential. then we try our best to learn and debug this issue. if there is no abnormal working condition, our IC will not latch off.

if you can provide the waveform during surge, it will also be useful to debug. the waveform we are interested in is the input bulk capacitor voltage to see how much voltage our IC will see at drain pin. another one is the drain to source voltage of our IC to see if there is any big ringing to cause any reverse current go from source pin into the IC. 

By the way, can you tell us if the surge is standard IEC surge and how much is it. Is this latch off problem repeatable? 

Best Regards