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TPS2491: necessity of external GATE pin clamp for High Gate Capacitance with Reverse Voltage Protection

Part Number: TPS2491
Other Parts Discussed in Thread: CSD18514Q5A, LM5069

Dear Specialists,

My customer is considering TPS2491 and has questions.

I would be grateful if you could advise.

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I am considering TPS2491 based on Reverse Voltage Protection Circuit(SNVA683).

Vin=12V and 24V

It uses two FET(Q1 and Q2) with back-to-back.

On the other hand, datasheet of P.18, 8.1.2.5 High Gate Capacitance Applications, 

If the total gate capacitance of FET exceeds 4000pF, external gate clamp diode is recommended. 

I'd like to use CSD18514Q5A, Ciss is 2060pF(typ) and 2680pF(max).

It uses two,total gate capacitance is 4120pF, external gate clamp diode is needed.

In this case, could you please advise what type of external circuit and constant is recommended.

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I appreciate your great help in advance.

Best regards,

Shinichi

  • Hi Shinichi,

    I strongly recommend to use LM5069 in this configuration as per SNVA683 document as it is proven design and being used by customers. Please let me know if you have any specific reason to select TPS2491 device.

    BR, Rakesh

  • Hi Rakesh,

    I confirmed E2E post and then

    Could you please see below.

    ---

    In this post,

    Yes TPS2491 should work in SNVA683 application in place of LM5069.

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    I think TPS2491 and LM5069 is the same function.

    And the customer conducted reverse voltage test and there was no problem.

    So, could you please advise about external gate clamp circuit in the datasheet P.18 8.1.2.5 High Gate Capacitance Applications.

    I appreciate your great help.

    Best regards,

    Shinichi

  • Hi Shinichi,

    Please use a Zener diode between GATE to Source of Q1 as external gate clamp circuit as shown below. Recommended part number is BZT52C15

    BR, Rakesh

  • HI Rakesh,

    Thank you for your reply.

    I'll share your suggestion with the customer.

    If the customer has an additional question, I consult you again.

    I appreciate your great help.

    Best regards,

    Shinichi

  • Hi Rakesh,

    I sent your answer to the customer, he has an additional question.

    Could you please advise.

    ---

    In my application circuit, There is RC noubination circuit for soft-start(1kohm and 22nF).

    The total Ciss of FET is 4120pF(typ) and 5360pF(max), can it be without Zener Diode?

    According to the datasheet, when total Ciss is up to 3000pF, Zener Diode is unnecessary.

    But I'd not like to use Zener Diode.

    If the answer is no, could you please let me know the maximum allowable Ciss.

    ---

    I appreciate your great help.

    Best regards,

    Shinichi

  • Hi Shinichi,

    I recommend to use external Zener diode as mentioned above for Ciss > 3000pF

    BR, Rakesh

  • Hi Rakesh,

    Thank you for your reply.

    I understand Ciss>3000pF, external diode is necessary.

    If the customer has an additional question, I cousult you again.

    I appreciate your great help.

    Best regards,

    Shinichi

  • Ok Shinichi