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TVS3300: TVS Diode App Note SLVAE37

lu tan
Prodigy 100 points
Part Number: TVS3300

Hi,

This post is regarding SLVAE37 app note, which references TVS3300.

Towards the bottom of page 6, it mentions RDYN of SMAJ33A to be 884mOhm and RDYN of SMBJ33A to be 0.504Ohms. I looked in the datasheets for these parts and did not find this number. I also tried dividing VCLAMP

with IPP and did not get these numbers. 

For TVS3300, on page 6 of its datasheet, RDYN is listed as 60mOhm max. Test Conditions column says this was calculated from VCLAMP at 15A and 30A surge current levels. I was not able to calculate this RDYN either.

Can someone please show me how RDYN was calculated for SMAJ33A, SMBJ33A,  and TVS3300?

(All datasheets and app note are attached.)

SMAJ33A_ds.pdfSMBJ33A_ds.pdfTVS3300_ds.pdfslvae37.pdf

  • 0
    TI__Expert 8471 points

    Hi Lu,

    RDYN of a surge diode will vary depending on the length of the pulse. In the case of SMAJ33A and SMBJ33A, their datasheets only spec for 10/1000 us pulses. The app note you are referring to is talking about RDYN for 8/20 us pulses. The engineer who wrote that app note is unfortunately no longer at TI, but the 8/20 us data for the SMA and SMB devices was most likely gathered internally in the lab for the document. 

    For TVS3300, RDYN = (Vclamp - Vbr)/Ipp, so at 15 A, RDYN = (40 V - 39 V)/15 A = ~0.067 Ohms and at 30 A, RDYN = (40 V - 39 V)/30 A = ~0.033 Ohms. The TVS flap-clamp devices are special in this way because as this surge current increases, the RDYN decreases since the clamping voltage stays the same. For a traditional diode like the SMA or SMB devices, the RDYN stays the same and the clamping voltage increases with surge current. 

    Regards,

    Matt Smith