ISO5500 - Fault pin continuously becoming damaged

Hi Sijomon, 

Can you share a schematic with us?

Thanks!
Jason Blackman 

of course. Schematics for both IGBT drive modules modules attached. I don't know how to upload two files. However for MOSFET modules the Fault Pin wiring is similar. Provision for pull up of 4K7 at Fault\ pin is not shown in the schematic, But its given in the final circuit

any clue? If required I can provide the entire gerbers of the power board. as well as the mosfet driver module.

did you get my schematic??

Hi Sijomon, 

Yes, I received your schematic. I will try to get back to you today. I didn't see anything that looked obviously wrong from my initial impression.

Thanks,
Jason Blackman 

Hello Jason,

True, I also couldn't suspect anything. When I found the pins getting continuously damaged, I probed the pin with a TEK scope (TPS 2014B) and a probe with 12pF capacitance. I found high frequency oscillations on the pin. The as a resort, P6KE6.8A is placed near to the each pins as snubbers. Things got somewhat working then, But biting stones in the porridge occasionally!!! Generally it should not happen isn't it?

Hi Sijomon,

Can you try to add a 4.7uF capacitor between the +15V and the -8V supplies? Basically between pins 12 and 9. There may not be enough buffering capacitance in your circuit when a large current is suddenly required. 

Let me know how that goes. 

Thanks!
Jason Blackman 

Hi Jason,

I had already thought about that. But the power supply being used is a 1W 800KHz flyback SMD module as you can see in the schematic. There can be oscillations in the output  on adding capacitance at its o/p. For an electrolytic cap, there is ESL that shields the capacitance from the supply output. But for ceramic caps, this may not be the case.  Alternatively, there would not be much benefit if we put electrolytic cap. However I will try out a ceramic cap of 4.7uf as you suggested and will let you know. Till then take care.

Hi Jason,

I did as you said. Instead of 4.7uF I tried with 10uF ceramic SMD. Also I put one 220E in between the 3K3(4K7 in our schematic) and 330pF(470pF in our schematic) in every drive module. ORing occurs at the other end of these 220E. It has been done as a mechanism to shield(as a damper) the  track inductance from the 330pF capacitor  which is suppose to be the cause of ringing. Just tell me if I am right (or wrong!). It has been working since 4 days.

Hi Jason,

Unfortunately it failed again. I changed the power supplies to 4 channel isolated flyback(input  40-60V) with an output voltage of 20V each. A pi filter has been put on each outputs to bring down the ripple to <20mV.  Then a 3T regulator of 15V (7815 1A) with 220uF capacitance provided near to the 3T input and 100uF+10uF ceramic 1206 smd  provided at the output reduces the voltage to the IC to 15V regulated. Still the fault pin failed. A hint is that, failure is observed during the transfers from inverter to mains/ or mains from inverter (Its an offline inverter). Circuit with TLP350 drives are working perfectly fine, but with no shoot through protection. We wish to have this IC as our drive so that we get an additional advantage of DESAT detection. Production is delayed for almost 6 months. What to do now? Help us.

Hi Sijomon,

I apologize for the delay. Can you take some oscilloscope shots of Vc and Ve relative to Vee-p, and also the Fault pin? We want to see what is happening on the IGBT side during the fault. 

Thanks,
Jason