innoswitch failure reasons

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Hi, we r designing an smps of 5V,3A based on der471 application note . Frequently InnoSwitchTM-CE INN2124K is prone to fail by shorting the BPP and the source pin . Please help me in finding the reson behind it.

May be this is one of the root cause, for 30 failures out of ~7000 pcs we built  with inn2215k for (USB-C 5V,3A) last month built in China during ATE. Did not see much issue on our previous build(120 pcs). 

We followed everything on the DER app note and the datasheet. But was not warned about this in the App note or datasheet.

Also we found so many failures failed during the burn-in, fyi, our burn-in spec is at 55C ambient, with intermittent ON-OFF. I believe it is mostly temperature.

The IC is getting very hot even with 2oz board with approximately 96.5mm^2 copper area for the source pin. Let me know, what is the recommended copper area. 

Is this a known issue on these ICs, if you have better recommendations, please feel free.

Please help ASAP. 

 

Hi,

 

Please share with us the exact schematic you are using, the exact transformer design and construction details and the PCB layout for us to figure out what is going wrong.

 

PI-AP

Hi,

 

Please share with us the exact schematic you are using, the exact transformer design and construction details and the PCB layout for us to figure out what is going wrong.

 

PI-AP

Hi PI-AP,

 

We cannot share our transformer design (exact) due to which will reveal too much of the product for a high profile customer. Just for your information, the Lp= 550uH, Np/Ns = 38/4. The transformer is hot, there should not be any issue, but only at 83C but the ICs are running super hot (102C) at 240V AC and 55C ambinet.

We are exactly following DER567, in terms of schematic. Surprisingly we did not see any issue in our last build 120 pcs, and in this build 47 EA ( 2 failed due to component missing, later fixed) failures. Looks like these IC has some kind of thermal issue, application operating temperarure is 55C.  

Do you have better solution for the 15W charger for this 55C ambient temp application.

Hi PI-AP,

Also,  would want to know, if other designs or customers use or you suggest any over-temperature protection circuit. 

If so, please send me the circuit for it. 

Thanks.

 

Hi David_s

 

We are currently shipping InnoSwitch ICs in very high volume and we have not seen the type of problem that you are describing. 

 

We suspect this is a design related problem.

 

In order to help you to resolve, I will need you to provide a copy of your schematic, layout and transformer design. In case you are unable to provide, kindly contact our factory to file an RMA and they can help resolve this issue.

 

Since we do not have information about the shape of the Copper area, it is difficult to estimate temperature rise. Is it possible to provide a picture of the section of the board layout with the InnoSwitch IC? As such our ICs have thermal shutdown protection and hence do not fail in the way that you describe. From your description it appears that the IC was found to have failed and on removal from the board, the BPP and S pin were found to be shorted. Is this description of the problem accurate?

 

The common reason for failure of the high voltage transistor is excess drain source voltage. The drain source voltage spike in a flyback is dependent on the clamp circuit used and the leakage reactance of the transformer. Can you send us screenshots of the VDS voltage of the primary side MOSFET (D-S pins) at the highest input voltage for your design.

 

 

It is also necessary that the transformer does not saturate under any operating condition. Can you provide us a waveform of the primary current with the ambient at 55deg.C which appears to be the condition at which failure occurs?

 

PI-AP

Thanks a lot for the information and help. After discussion with the support team in Shenzhen, our engineering team has decided not to use the IC.

We had used PI solution before, but these innoswitch ICs are running superhot.

 

Thanks again.