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LM74700-EP: Reverese current protection circuit

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

• 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.