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LM74502-Q1: Load Dump Protection Circuit

Part Number: LM74502-Q1
Other Parts Discussed in Thread: LM74502H-Q1, LM7480-Q1, LM74502


For my design, I will use LM74502-Q1 IC that protects my circuit for 160V load dump (ISO 16750-2. Us = 160).

I will not use reverse voltage protection feature so can I use this circuit only to prevent load dump without using reverse voltage protection?

Can you suggest a FET for an overvoltage protection circuit for my application? (Safe Operating Area)

Is 220uF Cout necessary? (In my design -> 5x2.2uF 100V ceramic capacitor)

Can this circuit also pass ISO 7637-2 Test Pulse 1 Us=-600V , Test Pulse 2a Us=+112V ,  Test Pulse 3a Us=-300Us ?

Best Regards.

  • Hi Egemen,

    For using LM74502-Q1 to protect the down stream circuit from 160V load dump , you will have to use the surge stopper configuration as  shown below. Please refer to circuit design and FET selection guidelines in datasheet section '10.3 Surge Stopper Using LM74502-Q1, LM74502H-Q1'.

    Yes, the circuit can pass pass ISO 7637-2 Test Pulse 1 Us=-600V , Test Pulse 2a Us=+112V ,  Test Pulse 3a Us=-300Us  by using proper TVS at the input. For input TVS selection guidelines, please refer to section '10.2.4 Selection of TVS Diodes and MOSFET for 24-V Battery Protection Applications' of the datasheet.

  • Hi,

    I do not need reverse voltage protection so can I remove Q2?

    For section 10.2.4 the TVS and FET are not suitable for desired application.

    What about this? "Is 220uF Cout necessary? (In my design -> 5x2.2uF 100V ceramic capacitor)"

    Best Regards.

  • Hi Egemen,

    You can remove Q2 if reverse voltage protection is completely not required. But when you want to pass  ISO 7637-2 Test Pulse 1 Us=-600V which is nothing but a reverse voltage applied at the input, you will need Q2. 

    You can follow guidelines provided in section 10.3.3 MOSFET Selection for mosfet in surge stopper configuration. For TVS selection please refer to section ' Input TVS Selection' in LM7480-Q1 datasheet

    Regarding output capacitance, there is no minimum requirement for LM74502 operation. You can choose the capacitance based on your application requirements. 

  • Hi thanks for the reply,

    Instead of Q2 after the TWS I will place the Schottky diode. Is that okay for the application?

    And which one do you recommend LM74502-Q1 or LM74502H-Q1 ?

  • Is there any progression for this question?

  • Also, I have one more question.

    What must be 220nF capacitor's voltage rating?

  • Hi Egemen,

    Yes you can replace Q2 with a Schottky diode in the power path.

    LM74502-Q1 has slow GATE turn ON speed and is recommended to be used for inrush current control especially when you need to startup with capacitance at the output. In case you just need a fast turn ON and turn OFF switch without any inrush current limit requirement, I would recommend using LM74502H-Q1. 

    The maximum voltage that will ever be generated across the VCAP-VS capacitor is 13.9V. SO, you can use a capacitor with voltage rating > 15V.