Solving Remote IC ESD Burning Problem

[Ravaner]

Hello. I encounter a strange problem I'll try to explain simply. I've design 2 electronics racks that have only in common the mains network and the ground. These 2 racks are separated by a distance of more than 2 feet. In one rack in which are installed several high voltage power supplies, some sparks can occur. Each time a spark occurs in this rack an OpAmp (LM-324) installed in 2nd rack is definitely destroyed. How can we explain that ? I insist on the fact that except ground (connected to earth) there is nothing common to the 2 racks and only this OpAmp is burned other IC's and transistors (placed on same board) are absolutely not affected.

 

[yungman]

Unless I can see the system how they connect, really cannot trouble shoot like this. The best way is put transorbs at the input of those op-amps. For passing the CE cert, We were required to put transorbs on anything that went in and out of every single pcb.

 

[berkeman]

Hello. I encounter a strange problem I'll try to explain simply. I've design 2 electronics racks that have only in common the mains network and the ground. These 2 racks are separated by a distance of more than 2 feet. In one rack in which are installed several high voltage power supplies, some sparks can occur. Each time a spark occurs in this rack an OpAmp (LM-324) installed in 2nd rack is definitely destroyed. How can we explain that ? I insist on the fact that except ground (connected to earth) there is nothing common to the 2 racks and only this OpAmp is burned other IC's and transistors (placed on same board) are absolutely not affected.

Sounds like an RF susceptibility problem in the 2nd rack. What level of EN 61000-4-3 Radiated RF Immunity testing did your devices pass?

 

[Ravaner]

I also suspect RF field (like in Hertz experience) but why always this OpAmp and not others which are very close and share same power supplies. Has LM-324 a specific sensibility for ESD ?

 

[yungman]

I don't believe it's RF radiation. Takes a lot more power to do it. It is power that burn the input. 324 is a BJT input, it is not the easiest to burn. It has been around for like 30 years and is being used all over.

There are lots of ways to burn an IC. You don't even need high voltage, we had problem burning ICs just by momentary connector contact bounce on a low voltage power pin. Particularly if you have coax cables. Coax is 30pF per foot. If you have 10' and charge at 5V. If you dump it to an input of an IC that is not powered up, that avalanche of current can pop an IC everytime in the right condition.

We had problem when we had the solder's weapon system that interface burn because of the connector contacts bounced when firing the M16 and we burn interface IC from just low voltage supply.

That is the reason I said it is so hard to nail down the cause. But the fix is so easy. Just put a Transorb for protection. We had so much argument at the time and they refused to put the transorb in until the other manager took a vacation and I put it in and solve the problem! Try that first and if that still don't work, then worry about it. You can spend days ( in our case, because it's military...months) trying to figure this out and it's so much easier to try the fix. It's power that burn, not likely HV as this is not CMOS and you said there is no HV even close to the connector.