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LM74700-Q1: Increasing the Current Limit

Hossein Saberi
Prodigy 120 points
Part Number: LM74700-Q1

I have used two LM74700 Evaluation Modules in an ORing application configuration. It works pretty well for our application. There is only one issue that I worry about. The maximum current for the LM74700 Evaluation Module is mentioned to be 5 A in the module specifications. I have checked all parts of the module, Max current for the Q1 switch on the board is 15 A, there are also input and output capacitors, TVs diode, and also the LM74700-Q1 that should not limit the Max current to less than 15 A. Can you please tell me what does limit the Max current two 5 A? 

In one of our application we need 20 A current at a 28 V load. So, I am wondering how I can increase the current in that design? Appreciate your help in this regard.

Thanks

  • 0
    TI__Genius 16305 points

    HI Hossein,

    I am looking into your question and will get back to you today.

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    TI__Genius 16305 points

    Hello Hossein,

    5A limitation is mainly based on some of the automotive test requirements, but the design can support higher current >10A also with Q1 MOSFET if the application is not automotive.

    We have a bigger footprint MOSFET Q2 also to increase the current capability beyond 15A.

    DMT6005LPS allows for usage at higher currents or you can choose another MOSFET with higher current capability of the same footprint.

    For 28V, you may have to change the TVS from 33V rated D1 to using D3 and D4.

    Could you let us know the end application where you plan to use LM74700-Q1.

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    Prodigy 120 points

    Hi Kari,

    Thank you for the helpful information. I see Q2 has higher current capability as you said. So, I will use Q2 in our design or find another MOSFET with higher current capability as we prefer to have 20 A Max current. 

    About the application, it is for our avionic system. To provide redundancy for the system each load is fed by two power lines and the nominal voltage is 28 V. Your device works pretty well in this application, I should only make some changes to adjust the current and voltage ratings.

    Regarding the TVS, you are saying we should remove D1 and put D3 and D4? Do you think D3 and D4 will work well for a 28 V system? 

    Thanks,

    Hossein

  • 0 in reply to Hossein Saberi
    TI__Genius 16305 points

    Hello Hossein,

    TVS D1 is a 33V rated bidirectional TVS and may not suit 28V power rail because 28V rail maximum voltage can exceed the TVS clamp voltage and interfere in the normal operation.

    D4 is is mainly for reverse input polarity protection and can be removed if not need in this avionics system.

    So D1 or D3 can protect positive transients spikes.

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    Prodigy 120 points

    Hi,

    I understand your point on the voltage rating. Appreciate your help in this regard Kari, that really helped me to get what we need for our system. 

    Thanks!