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OPA172: Is the maximum current changing with the change of temperature or current of the constant current source

Genius 5160 points

Replies: 3

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Part Number: OPA172

Dears:

Could you kindly help to give some advise? 

Form the below picture when OPA172 is in a constant current source circuit and under the situation of adjustment end is invariant, is the maximum current changing with the change of temperature or current of the constant current source?

Thanks a lot!

Best regards

Luck Wu

Thanks a lot!

Best regards

Luck Wu

  • Luck Wu,

    I am sorry; I did not understand the question.

    The horizontal slope section of the curve is set by the on resistance of the MOSFET channel. This resistance increase with temperature.
    The vertical section of the curve is pinched channel (constant current) operation of the MOSFET this current decreases with temperature.

    The chart shows the measurement of VOUT (relative to power supply rail) with a fixed current swept.
    Because the curves fold back a little, I suspect the chart data is really a output voltage sweep with the output current measured.
    The difference in results from the two measurement methods is minor.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Luck,

    In addition to Ron's comments, as long as the current source is operating in a linear operating region for the op amp then the current will not change very much with temperature.  There will be small changes in output current vs. temperature due to changes in the input offset voltage of the op amp vs. temperature but these changes are likely smaller than you are concerned about. 

    Regards,
    Collin Wells
    Precision ADC Applications

  • In reply to Collin Wells:

    Luck Wu,

    If you need more assistance, let us know. If the question is answered, please mark the answer.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

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