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CSD18540Q5B: CSD18540 using with the LM74800QDRRRQ1 Driver IC

Ramana Murthy
Expert 1765 points
Part Number: CSD18540Q5B
Other Parts Discussed in Thread: CSD

Hello Team TI,

I'd like to inquire about a difference in voltage drop observed between two MOSFET back to back Mosfet with common drain configurations in a circuit using the LM74800QDRRRQ1 Driver IC. Simmilar to the below configuration.

In the first configuration, employing a PSMN series NXP MOSFET, I haven't measured any noticeable voltage drop.

On the other hand, when using a TI CSD18540Q5BT MOSFET in the identical schematic, I've observed a voltage drop of around 0.6 to 0.7 VDC across the MOSFET at currents up to 2A.
Can you help me understand why there's a difference in voltage drop between these two MOSFETs in the same circuit?

Thanks,
Murthy

  • 0
    TI__Mastermind 32965 points

    Hello Murthy,

    Thanks for your interest in TI FETs. It sounds like one of the FETs might not be turned on and you're measuring the forward voltage drop of its body diode. Can you check VGS (DGATE and HGATE) of the two FETs to make sure they are both being driven to at least 4.5V? The CSD18540Q5B is a low on resistance FET and the voltage drop should be very small when it is turned on and conducting 2A of current. Please let me know what you find.

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    TI__Mastermind 32965 points

    Hello Murthy,

    Following up to see if your issue has been resolved. Please let me know.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Expert 1765 points

    Hello Sir,

    I'm writing to inquire about the LM74801QDRRRQ1 and its behavior with the C pin (pin 12).

    In my testing, I've observed a voltage drop when leaving the C pin unconnected to the common drain of the external MOSFETs. While shorting the C pin to the common drain resolves the issue, this configuration raises a concern about reverse current blocking.

    My understanding is that an unconnected C pin is necessary for the ideal diode controller to achieve reverse current blocking functionality.

    Could you please clarify the recommended connection for the C pin and advise on how to ensure proper reverse current blocking while avoiding the voltage drop issue?

    Thank you for your time and assistance.

    Sincerely,
    Murthy

  • 0 in reply to Ramana Murthy
    TI__Guru** 103241 points

    Hello Murthy,

    C pin should be connected to common Drian point for proper function

    Please correct that C connection and check the voltage drop. 

    What is the part number of NXP MOSFET

    Best Regards

    Rakesh

  • 0 in reply to Rakesh
    Expert 1765 points

    Hi Rakesh,

    How to enable the reverse current blocking function in the LM74801QDRRRQ1 IC ??.

    The datasheet mentions that the C terminal is floating. Attached is a screenshot for reference (C terminal floating).

    If C terminal is floating, both the PSMN series MOSFET and the CSD18540Q5BT MOSFET behavior is similar?


    Thanks,
    Murthy

  • 0 in reply to Ramana Murthy
    TI__Mastermind 21250 points

    Hi Murthy,

    To enable reverse current blocking in LM74801QDRRRQ1 IC, you will have to connect C terminal to the drain of FET as shown.

    Yes, if C terminal is left floating, PSMN and CSD FET will behave similarly.

    Regards,

    Shiven Dhir