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LM74700-Q1: TVS selection

Mahdi fakharmanesh
Prodigy 20 points
Part Number: LM74700-Q1

Hi All,

In LM74700' datasheet page 18 (Selection of TVS Diodes for 12-V Battery Protection Applications), it mentions that pulse 1 is -150V with 10 ohm impedance, while when I check ISO7637 pulse 1 is -100V with 10 ohm impedance.
and it says we need a TVS with clamping voltage of less than 44V, while SMBJ33CA’s clamping voltage is 53,3V(breaking voltage is 42,2V).

So the question is that are these information correct or did I miss some points?

  • 0
    TI__Guru 57737 points

    Hi Mahdi,

    The TVS clamping voltage depends on the current flowing through it. The current flowing through the TVS depends on the Voltage across it and the path impedance. When a -100V ISO Pulse 1 is applied at input, the TVS clamps the voltage to 42V as you can see in the test waveform capture below. The voltage across TVS is = (-100V-(-42V)) = -58V and considering the 10 ohms impedance of the ISO Pulse 1 generator, the current flowing through the TVS would be = 5.8A. So, for 5.8A current flowing in the TVS, the clamping voltage across it is 42V. In the datasheet, the current mentioned is 15A which is a typo. We will change it in the next datasheet revision.