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LM74701-Q1: LM74701-Q1 Problem

Part Number: LM74701-Q1

Hi  engineer:

     I am evaluating LM74701-Q1 for my project, and I tested your EVM these days. 

     I have several questions about this part, waiting for your reply.

     1. Full conduction mode:  I tested the EVM, the Voltage difference between Cathode and Anode is I * rds(on), not 50mV, and when load is up to 60mA, the Gate voltage is equeal wiht VCAP,  so I think the mosfet is full condution.

     2.  Vds Clamp mode: if Anode is Negative votlage,  the voltage is under Anode POR threshold, How does the Mosfet be driven on?

     3 . The absoute voltage of Anode is 65V, if we don't add TVS, how to pass ISO7637-2 2A /2B test?

     Thanks

     Johnsin  Tao

  • Hi Johnsin,

    Let me respond to your queries by tomorrow. 

  • Waiting for your reply, thanks.

  • Hi Torres,

    Please find my response inline below,

    1. Full conduction mode:  I tested the EVM, the Voltage difference between Cathode and Anode is I * rds(on), not 50mV, and when load is up to 60mA, the Gate voltage is equal with VCAP,  so I think the mosfet is full conduction.

    The LM74701-Q1 will try to regulate the FET source-drain voltage to around V(AK REG) = 20mV. Once the load current is high enough that the product of  Iload * Rds(on) is greater than 20mV, the LM74701-Q1 will start to pull the gate high to VCAP. This is full conduction mode, 

    2.  Vds Clamp mode: if Anode is Negative voltage,  the voltage is under Anode POR threshold, How does the Mosfet be driven on?

    When the Anode voltage drops below cathode voltage by VCLAMP = 40V, the internal circuit drives the gate-source voltage such that the voltage across the FET is maintained at  VCLAMP voltage. The internal VDS Clamp circuit is designed to operate even when Vanode is negative. 

    3 . The absolute voltage of Anode is 65V, if we don't add TVS, how to pass ISO7637-2 2A /2B test?

    ISO7637-2 2A /2B are very short duration and low energy pulses. These can be easily suppressed using  input and output capacitances.