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REF200: Not able to get constant current

Pranoti Katke
Prodigy 30 points
Part Number: REF200

Tool/software:

Hi,

I am using REF200 as constant current source for thermistor interface.

I am able to get better results from 10Kohm. to 680ohm.

But the need is from 43kohm to 680ohm.

How to keep constant current at higher resistance value as well?

Below is circuit diagram:

Regards,

PK

  • 0
    TI__Expert 3910 points

    Hi PK,

    Thanks for reaching out!

    I'm not sure I understand your question fully. What do you mean by "better results" for the 10Kohm to 680ohm range?

    Also, what current are you seeing instead of 100uA that is not staying constant?

    Best Regards,

    Andrew Li

  • 0 in reply to Andrew Li
    Prodigy 30 points

    Hi Andrew,

    Thank you for quick response.

    Below are readings I took at different resistance and current is not constant.

    Regards,

    PK

  • 0 in reply to Pranoti Katke
    TI__Expert 3910 points

    Hi PK,

    Thanks for the extra information!

    It seems that your compliance voltage might be too low. Please try to increase the value of V+ to see if this helps resolve the issue.

    To maintain a current of 100uA at a resistance of about 42KOhm, the required voltage would be about 4.2V.

    I hope this helps!

    Best Regards,

    Andrew Li