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LM74700-Q1: Behavior when noise is applied to the input

Y.Ottey
Mastermind 6145 points
Part Number: LM74700-Q1

Dear TI Team

I would like to ask about the behavior when noise such as lightning surge, static electricity, and burst noise is applied to VBAT in the application shown below.


Can you answer the following questions?
1. When the above noise (±100V) is input to VBAT, it is considered that it is suppressed by the TVS diode on the input side.
If noise (about ±100V) is input again after noise is suppressed by the TVS diode, does the external FET or LM74700 be damaged or the LM74700 malfunction?

2. Is it possible to replace the TVS diode installed in the application shown below with a varistor?

Best Regards,

Y.Ottey

  • 0
    TI__Genius 16305 points

    Hello Ottey,

    LM74700-Q1 has 65V maximum operating voltage and it will get damaged if 100V is applied at the input.

    In the negative direction also, it is -65V. Negative surge pulse also would be required to clamped by varistor.

    TVS would be too small to take the energy in surge voltage, so varistor is commonly used to limit the surge voltage to less than the maximum operating voltage of the circuit. With LM74700-Q1, you need to limit it to less than 65V.

    Next on the MOSFET, If the MOSFET is ON, then it will pass the energy to the output side.

    If the MOSFET is off, then surge pulse is passed to the output through the body diode of the MOSFET.

    Surge current should not exceed MOSFET body diode (source current) maximum current rating.

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    TI__Genius 16305 points

    Hello Ottey,

    Additional comment on the TVS.

    In automotive reverse battery protection application, Bidirectional TVS is used to clamp the negative transients (-100V or -150) pulses and reverse connected battery conditions.

    Varistor needs to be bidirectional if reverse battery protection is required.

    If you think all your question are answered, click "this resolved my issue button" at the end.

    Or if you have more questions, let us know.

    Regards,

    Kari.