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TIDA-00281: TVS selection

Part Number: TIDA-00281
Other Parts Discussed in Thread: LM74700-Q1

Hi Trenton,

Thanks for designing the TIDA-00281. I have a question on the TVS selection. SMBJ28A-13-F was selected for D1 and SMBJ14A-13-F was selected for D2. I checked the TVS datasheet and found out that the peak pluse current Ipp for SMBJ28A-13-F is 13.2A and for SMBJ14A-13-F is 25.8A. I believe the current for the system is more than 20.8A (1000W/48V). That means that Ipp of D1 is below maximum surge current. Did I miss anything? I will appreciate if you could explain whether it is a typo.

Thanks and I look forward to hearing from you,

John

  • Hi John,

    Thanks for reaching out to E2E!  My name is Aaron Grgurich and I am an applications engineer with our High Power Drivers team.

    To double-check, I believe the D1 and D2 diodes you are referring to are on the 12V battery input for the 12V supply to run the 12V Flyback converter, and are therefore not in the picture in regards to the high current output transients.

    Please let me know if this answered your question by clicking the green button or feel free to follow up with additional questions!


    Thanks,

    Aaron Grgurich

  • Hi Aaron,

    Thank you very much for your quick reply. Sorry I misunderstood that there is no high current output in the 12V battery.

    I do have another question on TVS recommendation. I am not sure it belongs to this TIDA-00281 post.

    In LM74700-Q1 datasheet page 18, it says that for 24V battery system, the minimum breakdown voltage for TVS+ is 48V and the maximum breakdown for TVS+ is 65V. The minimum breakdown voltage for TVS- is -32V and the maximum breakdown voltage for TVS- is 43V. I believe that SMBJ45A, SMBJ48A, SMBJ51A, and SMBJ54A all meet the requirement for TVS+ in addition to the recommended SMBJ58A. And SMBJ30A, SMBJ33A, and SMBJ36A all meet the requirement for TVS- in addition to the recommended SMBJ26A. Could you please confirm whether my understanding is correct.

    For 12V battery system, the minimum breakdown voltage for TVS+ is 35V and the maximum breakdown for TVS+ is 65V. The minimum breakdown voltage for TVS- is -16V and the maximum breakdown voltage for TVS- is 44V. Using the same logic, all SMBJ33A, SMBJ36A, SMBJ40A/43A/45A/48A/51A/54A to SMBJ58A meet the requirement for TVS+ of 12V, and all SMBJ15A, SMBJ16A, SMBJ17A, SMBJ18A/20A/22A/24A/28A/28A/30A/33A, and SMBJ36A meet the requirement for TVS- of 12V. To reduce the number of TVS, only one TVS (SMBJ33CA or SMBJCA36) is needed for 12V battery.

    If multiple TVSs are acceptable, I would choose lower number such as SMBJ45A for 24V TVS+ as it has higher maximum peak pulse current rating. Please comment.

    Thanks and I look forward to hearing from you,

    John

  • Hi John,

    You have another thread for the questions on TVS diode. Please close one of thread to avoid duplication.

    https://e2e.ti.com/support/power-management/f/196/p/947312/3500003#3500003

    Best Regards, Rakesh

  • Hi Rakesh,

    Thanks.

    John