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LMP91200: ph Level measuring

Antonio Faggio
Expert 7210 points
Part Number: LMP91200

Hello All,

My customer is working on a new low-cost pH measuring device. Currently the measurement stage is done with a quadruple operational TLC2264ID in SOIC-14 package.

Customer has the problem that at 50 °C the bias current Ib causes the measurement to drift when they supply the signal with pH simulator with impedance equal to 1Gohm.

Customer has tested a competitive tool and it does not have this drift, and the measurement is much more stable.

The competitive tool uses another operational amplifier which has a compensation function that keeps the Ib constant at 5pA up to 85 ° C.

Customer at the beginning was looking for an OpAmp to replace this competitive p/n.

But now customer is more focus on specific p/n similar to LMP91200 for pH sensing.

Do you have a comment here?

Many Thanks,

Antonio

  • 0
    TI__Genius 9675 points
    Hi Antonio,

    Am looking into this and will get back with you shortly.

    Thanks,
    Jalen
  • 0 in reply to Jalen Tate89
    TI__Genius 9675 points

    Hi Antonio,

    The LMP91200 was designed with the output impedance of a pH electrode to be ranging from 10 MΩ to 1000 MΩ. There is a low input bias current which allows the voltage error produced by the input bias current and electrode resistance will be minimal.

    The LMP91200 should address the customers concerns with the following key specs that can be found in the datasheet.

    Depending on setup you can expect no more than a 6.5 pA input bias current worst case.

    Jalen