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# I would like to kwow if my SM6T18A/CA on the input connector of my product is compliant with the no destruction of my electronic which is located just after when fast Transient 61000-4-4 is applied.

Associate

Hi Sir,

I currently use a SM6T18A/CA on the 12V+/- 5% power supply input of my product.

After this protection are located many electronic components with absolute maximum rating voltage levels (continuous) given from 13,2V to 18V.

After applying the transient voltage Test 61000-4-4 (+/-1KV levels), I can observe that one component is destroyed. I can not that it corresponds to the only component which is not HBM compliant (+-2KV).

All others components are compliant with HBM and are not destroyed even if I think the resulted clamping voltage on the SM6T18/CA regarding 61000-4-4 (+/-1KV levels) is over their absolute maximum rating voltage levels (continuous) given from 13,2V to 18V.

• What is the clamping voltage level on the SM6T18A/CA regarding 61000-4-4 (+/-1KV levels)?
• Is this transient clamping voltage can be considered as an issue for the electronic components after which have a maximum rating voltage levels (continuous) from 13,2V to 18V?
• May I consider that HBM (+/-2KV) is a guarantee to support the clamping voltage after the SM6T18A/CA protective diode (because all the current has been drived by the protective diode, and no much energy is still present on the 12V power supply rail)?

Thank you very much for your support.

Anthony.

1 ACCEPTED SOLUTION

Accepted Solutions
ST Employee

Hi Anthony,

What is the clamping voltage level on the SM6T18A/CA regarding 61000-4-4 (+/-1KV levels)?

• We can consider that : Clamping voltage = breakdown voltage + 2.2V in worst case
• Indeed, the output impedance of the generator is 50Ω. Then, 1kV / 50Ω = 20A. Rd_8_20(SM6T18A/CA) x 20A = 2.2V

Is this transient clamping voltage can be considered as an issue for the electronic components after which have a maximum rating voltage level (continuous) from 13,2V to 18V?

• AMR is the most stressful case because it is DC 1min. Then it can be over design for short surges like IEC 61000-4-4. As example, HBM are usually granted up to 2kV with RC time constant delay = 150ns.

May I consider that HBM (+/-2KV) is a guarantee to support the clamping voltage after the SM6T18A/CA protective diode (because all the current has been driven by the protective diode, and no much energy is still present on the 12V power supply rail)?

• Unfortunately, it cannot be a guarantee. There is no direct correlation between HBM and robustness and other surge waveform. Internal ESD protection for HBM must co-work properly with SM6T18A/CA external protection.
• An experimental validation is then required.

SM6T15A/CA should be better than SM6T18A/CA because :

• Clamping voltage should be 3.7V lower than SM6T18A/CA (lower breakdown voltage and lower dynamic resistance) and
• 12V+/- 5% power supply (12.6V max) is below max stand-off of SM6T15A/CA (12.8V)

Best regards,

Mathieu

2 REPLIES 2
ST Employee

Hi Anthony,

What is the clamping voltage level on the SM6T18A/CA regarding 61000-4-4 (+/-1KV levels)?

• We can consider that : Clamping voltage = breakdown voltage + 2.2V in worst case
• Indeed, the output impedance of the generator is 50Ω. Then, 1kV / 50Ω = 20A. Rd_8_20(SM6T18A/CA) x 20A = 2.2V

Is this transient clamping voltage can be considered as an issue for the electronic components after which have a maximum rating voltage level (continuous) from 13,2V to 18V?

• AMR is the most stressful case because it is DC 1min. Then it can be over design for short surges like IEC 61000-4-4. As example, HBM are usually granted up to 2kV with RC time constant delay = 150ns.

May I consider that HBM (+/-2KV) is a guarantee to support the clamping voltage after the SM6T18A/CA protective diode (because all the current has been driven by the protective diode, and no much energy is still present on the 12V power supply rail)?

• Unfortunately, it cannot be a guarantee. There is no direct correlation between HBM and robustness and other surge waveform. Internal ESD protection for HBM must co-work properly with SM6T18A/CA external protection.
• An experimental validation is then required.

SM6T15A/CA should be better than SM6T18A/CA because :

• Clamping voltage should be 3.7V lower than SM6T18A/CA (lower breakdown voltage and lower dynamic resistance) and
• 12V+/- 5% power supply (12.6V max) is below max stand-off of SM6T15A/CA (12.8V)

Best regards,

Mathieu

ST Employee

Hi All,

This question was routed to our online support center for direct support. The above response from MROUV.1 is the direct response from the division of this request.

Regards,

Jake

ST Support