PFS71X Exploding
Hi there,
After several tests, I keep having the same problem, after several moments working, the IC explodes!! I don't understand this as there are plenty of protections. We have an inductive load(less than 100w), controlled wtih a H bridge, which is fed by the PFC circuit dsigned with a PFS712(output 340V). The PFC also feeds a flyback circuit(made with a LNK625, which works perfectly alone). This flyback is used to feed the MOS drivers of the H bridge, and with the same secondary(which is refered to the power ground) I feed the PFS712.
With the second source of the flyback we feed the control circuits(signals).
We desgined the PFC considering the AN52 and AN53 and the PFS datasheet. The differences we find are: The diode after the boost inductance has a 75ns trr instead of 27ns, Due to space requirements we are not placing thermal dissipator, and the PFS Vcc feed comes from the flyback secondary which is referenced to the same power ground as the PFS source pin(so we don't conect the feedback circuit to the ground as it goes throud the PFS, to avoid making a loop.
So what can we be doing wrong to achieve these catastrofic results?
Comments
Great, thanks for your reply, concerning your question, the ic also exploded only by turning on the circuit...
Anyway, here I upload the schematics and layout. The schematic is a newer version, so the components won't match the layout, but the missing components in the layout are fitted there(I know it's not the best way, but anyway I checked they are well connected, etc)
For the moment, my main doubt is how do I have to feed the IC, concerning the grounding.
How can I feed the IC with the same output of the flyback that I use for the ic's located in the power module, and which is referenced to the same ground that the source of the PFS??
The right way of grounding PFS is to put FB and Vcc ground to G pin instead of S pin, and do not loop it far away to second stage. If you look at our RDK236 layout, G pin is the ground for FB, Vcc, Vpin decoupling cap. And distance the control circuit from the high voltage and current traces. S pin is going to be the power ground for PFC output ground. Also, please remember to attache PFS heatsink to S pin close to PFS IC.
With what you mentined here, I think you can try one thing first: Run circuit at light load say 20% load, do you still have the same failure? If problem only happens at heavier load, could you add a heatsink to PFS712 for debugging purpose? By doing that we can rule out the failure is due to over temperature conditionnn or not. If all above can not explain the problem, then I need to look at your schematic and especially layout to make further recommendation.