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XTR108 datasheet question.

Massimiliano Golfetto
Prodigy 100 points
Other Parts Discussed in Thread: XTR108

Hello, I'm having trouble on reading XTR108 datasheet.

I can't understand which equations to use for calculating values for N10, N11, N12 and N13.

There are two set of equations, first set at page 19 table XV in XTR108 datasheet and a second set on Evaluation Board Tutorial PDF at page 57.

Those two set are very different one each other.

Is there some circuit implementation on Evaluation Board that make equations has to be changed?

On XTR108 datasheet (page 20) there's an example but I think value Iref1,2 at point 6 should be 368,39uA (microA) and not 368,39mA (milliA).

Thank you.

  • 0
    TI__Mastermind 27715 points

    Hello Massimiliano,

    Both sets of equations are equivalent. The equations in the evaluation board tutorial PDF use substitutions for Izpgm = (5*Vref)/(8*Rvi) and Iset = (Vref/Rset), as well as some numerical factoring, in an attempt to simplify the math.

    For example, the equation for N11 in the datasheet reads:

    • N11 = round[((64*Iref*Rset)/Vref) - 320]

    Substituting (1/Iset) in for (Rset/Vref), we get:

    • N11 = round[((64*Iref)/Iset) - 320]

    Now multiplying 320 by 1 in the form of (Iset/Iset), we can combine the equation into one fraction:

    • N11 = round[(64*Iref - 320*Iset)/Iset]

    Finally, factor the numerator by 64 to arrive at the version which matches the EVM user's guide:

    • N11 = round[64*(Iref - 5*Iset)/Iset]

    For simplicity, you can use the equations given in Table XV of the XTR108 data sheet.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps