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LP3988IMFX-2.85 Questions

Richard Elmquist
Mastermind 45250 points

Other Parts Discussed in Thread: LP3988

I have a customer who wants to level shift the OFF conditions on the LP3988IMFX-2.85 and he needs to know the values of the internal resistor R1 and R2. Do we have these values?

Thanks for your help with this!

Richard Elmquist

  • 0
    TI__Mastermind 22610 points

    No, the LP3988 R1 and R2 values are not available.

    If I guess that 50% of the typical Iq(no load) current ((85uA / 2)= 42uA) is through R1 and R2, AND if I guess that typical Vref is 1.250V, then R2 would need to be about 30.0k ohms, which would make R1 about 38.4k ohms.

    Not sure how your customer is planning implement level shifting of the Enable Vil threshold, but there is more to the ground pin current that what's going through R1 and R2.

  • 0 in reply to Donald Jones
    TI__Mastermind 45250 points

    Don,

    I understand and will relay this to the customer.

    Thanks for your help with this!

    Richard Elmquist