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HiperLCS catastrophic failure

Posted by: mzapolsk on

Hello,

I am in the process of designing a 90W converter. I am using LCS702HG. In the past I experienced multiple failures, which turned out to be caused by very poor layout. After redesigning, the failure rate was reduced dramatically, but not entirely. In 3 months of testing, few hours every day, I blew up two converters.

My question is: what are known errors that can cause HiperLCS to explode, despite having all built in safeties (and they are confirmed functional)? I am in dire need of reproducing this failure in a controlled manner (not only getting rid of the design fault).

Comments

Submitted by PI-Neela on 03/09/2017

refer to datasheet fig 20 page 15, if design resutl in burst at fmax, high power dissiplation due to loss of ZVS will heat up the deivce rapidly. IT may not necessary resutls in blow up, but could have a chance of thermal run away.

Also for any LLC topology, if you work at gain inversion region, the gain has reversed slop and can result in failure. IT applies to any LLC products. YOu can use our PIXL design tool to aviod the design fault.  

Submitted by mzapolsk on 03/10/2017

Thank you for your reply.

I made sure that the power supply is not bursting at fmax, and not operating in gain inversion region. Actually the failure I observed happened when the device was operating under a low load (24V/1A). It was operating above resonance, but not yet in burst mode.

What I suspect are two things. First is the feedback loop stability (and I am looking into it right now). Second is noise entering into DT/BF pin (I mistakenly referenced bias supply voltage to signal GND. Rewiring that reduced the noise significantly). I suspect these could lead to loss of ZVS. Could that have the potential to blow the device up?

Also, I do not know what you wanted me to see in DER-447, as in page 43 I only see standby transformer design spreadsheet...

Submitted by PI-Neela on 03/13/2017

appology for DER447 message. IT is not for your project. Please let us know if your problem resolved or not after your modification.