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Original question:

LMC6001: Why -IN is short-circuit with GND? How I broken it?

LMC6001: Tell me please, where I can buy a thermal resistor R1

Alexander Zaderko
Prodigy 40 points
Part Number: LMC6001

Tell me please,

where I can buy a thermal resistor R1 (Fig.23 of Datasheet) 100kΩ +3500ppm/°C?

Micro-ohms do not support this 137 type of resistors.

is maximum 50k. So, I'm very confused (

Thanks

  • 0
    Guru 140200 points

    Hi Alexander,

    yes, it's hard to get these special resistors today.

    I would change the circuit in such a way that you can use a PT1000 or even a PT10000 instead of this special resistor. The PT1000 has a temperature coefficient of +3850ppm/°C. Put a 0.1% precision metal film resistor of 10390R (10k0 + 390R) with very low temperature coefficient (< 25ppm/°C) in parallel to the PT1000. This gives an overall temperature coefficient of +3500ppm/°C.

    If you take a PT10000, put a resistance of 103900R (100k + 3k9) in parallel.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 40 points

    Dear Kai,

    if I take even pt10000 resistor in parallel with 103900R resistance, it maybe give a result a thermal coefficient 3500/° with resulting resistance ab. 10k. But LMC6001 need 100k resistance with this TC.

    Or did I misunderstand your idea?

    Alexander

  • 0 in reply to Alexander Zaderko
    Guru 140200 points

    Hi Alexander,

    you can easily decrease the resistances R1, R2 and R3 in this circuit:

    The PT10000 in parallel with the 103900 resistance looks like a 9122.04 resistance. So, the resistors R2 and R3 can be decreased by a factor of 100k / 9122.04 = 10.96246. -> Take R2 = 6k2 and R3 = 500R.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 40 points
    Thanks, Kai,
    Its look like that the best solution is a stable 100k resistor and thermostat for cell. Because Pt10000 is even rare than type 137.
    But your recommendations is the possible way to resolve a problem. Thanks.
    I hope, TI take in to account this problem in next ultra low current OPA and make possible direct input of Pt1000.
    A.
  • 0 in reply to Alexander Zaderko
    Guru 140200 points
    Hi Alexander,

    a PT1000 in parallel with a 10390R resistance should also work. Take R2 = 620R and R3 = 50R then.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 40 points
    Thanks, Kai, this is very useful!