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LM74700-EP: Reverese current protection circuit

Jonathan Navor
Genius 9375 points
Part Number: LM74700-EP

Hi Team,

Good day! We need your confirmation and support.  As we understand from the datasheet there are TVS diode, one at the positive side and one at the negative side(TVS+ and TVS-). Is it applicable for both the diodes or only for TVS+. Moreover, I would like to know more about the purpose of TVS-. Since the maximum input operating voltage is 60v, as per the equation in the datasheet the maximum clamping voltage for the TVS- diode could only be 75V-60V, which is 15 V.

Thank you in advance for the support. 

Best regards,

Jonathan

  • 0
    TI__Guru 57737 points

    Hi Jonathan,

    1. Yes, TVS are required both on positive side and negative side.

    2. What do you mean by 'Is it applicable for both the diodes or only for TVS+' ? is there any sentence missing before ?

    3.  TVS- is specifically required if your system can be subjected to ISO 7637-2 Pulse 1 at the input of LM74700-EP. During ISO Pulse 1, the input voltage can go as low as –150 V with a generator/input impedance of 10 Ω. As the device is only rated for -65V, we need to use a TVS- to clamp the voltage on the negative side to within the device Abs Max rating of -65.

    Also, we need to keep in mind the voltage difference across the FET during pulse-1. Before the Pulse1 is applied, the input voltage = ouptut voltage = say a maximum steady state positive voltage of 16V. During pulse 1, the input can go as low as -150V but using a TVS- we will clamp the voltage to within -65V. now the voltage across the FET = 16V- (- TVS- clamp voltage). If you are using 60V rated FET, then the TVS - should clamp the negative input voltage to well within -44V.