ISO1050: how to improve the system level ESD performance for ISO1050

Kote: Thanks for requesting additional clarification.

Oliver,

Thanks for using our E2E forums.  In addition to Kote's questions above, can you clarify the 'fail' mechanism - was the ISO1050 or the TVS damaged after the test? What level of performance is the desired target - 8kV contact ?

Assuming you are striking the CAN pins w.r.t local ground ( = "GND_CAN"), and given the known performance of the part,  one way to improve the IEC ESD performance is by picking good external protection components,  specifically the TVS in this case.

When an ESD strike occurs, we want the TVS to trigger first and steer the current away from the DUT (ISO1050) to the local ground (GND_CAN). When this happens, the TVS breakdown and clamp voltage are important. These two parameters are dependent on the peak current seen by the TVS (Ipp) and are documented in the TVS datasheet. Generally with higher level of ESD strikes, higher peak currents (Ipp) are seen, and so when the TVS kicks in, the clamp voltages are higher, as can be seen in the TVS datasheets.

• TVS should breakddown slightly  beyond the common mode operating voltage of the part (+/- 12V in this case), so that it does not interfere with normal operation.
•  At the same time, the clamp voltage rating of the TVS should be within/inside  the Abs Max rating of the ISO1050 ( -27V to +40V), so that the TVS protects the part as intended. If the clamp rating of the TVS exceeds the Abs max of the part, then issues can occur.

I took a look at the TVS used in the schematic above. I picked an example here and you can see the clamp voltage rating is 40V. This is marginal on the positive side, but will be tricky on the negative side since it will be beyond the -27V. Also at higher currents (higher strike levels), the clamp rating rises to 70V, which can damage the part.

• In addition, some example solutions that break outside the Recommended region (to not interfere) but safely clamp before the Abs Max region (to protect the device) are listed here and here.
• Finally, we can place the caps and TVS as close to the DUT as possible for effective protection and to cut trace series inductance down.

Hope this helps.

Regards,

Abhi