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INA240: Customer question regarding spec sheet

Yosuke Tanaka
Prodigy 60 points
Part Number: INA240

Regarding specification sheet,

Only typ. Value is described, but no max value is described.

 

INA240A1QDRQ1

Q1.　What is the max value of Settling time - output settles to 0.5% of final value   ？

 

Q2. What is the max value of output resistance?        

  • +1
    Guru 140200 points

    Hi Yosuke,

    the INA240 is not optimized for fast settling. With a fast ADC you might need an additional ADC driver.

    Kai

  • +1
    TI__Prodigy 660 points

    Hello Yosuke,

    Thanks for the question and using the E2E forum.

    Max settling time:

    Max settling time is not spec'd for this device however, typical specification value normally covers plus or minus one standard deviation, OR plus or minus sigma on a Gaussian distribution of a single test population. So building in +/-30ish percent to typical value could account for maximum value due to temp and process variations. 

    Max output resistance:

    Here is a plot showing what might be expected for output impedance on one of our devices:

  • +1 in reply to Joseph Scherphorn
    TI__Prodigy 60 points

    Thank you for your response.

    Sorry , For confirmation

    Max value of settling time is 9.6*1.3=12.48 for INA240A1-Q1 for example?

  • +1 in reply to Joseph Scherphorn
    TI__Prodigy 60 points

    Regarding Max output resistance

    I cannnot read out max value from graph.

    Could you inform the max value of me?

    Sorry to have trouble to you, customer need the concrete value for desgin.

  • 0 in reply to Yosuke Tanaka
    TI__Prodigy 660 points

    Plot shows max impedance of around 185 ohm (note: this is typical behavior)

    Maximum settling time may by approximated by building in percentage as you have done above, but note this is also approximation based on knowledge that about 70% of device population will fall below typical spec.

  • 0 in reply to Yosuke Tanaka
    Guru 140200 points

    Hi Yosuke,

    the very most parameters of OPAmps do not come with a maximum specification in the datasheet. Instead of insisting in a maximum specification which you will not get anyway from the manufacturer in the very most cases, design your circuit in such a way that it can tolerate huge tolerances of the parameter in question. When it comes to slew rate or output impedance I always assume a tolerance of 100% in standard applications, not only to handle manufacturing tolerances but also long term drifts. If your circuit cannot tolerate this tolerance then change your circuit Relaxed

    All this standard deviation stuff is statistics and does not say anything about the chip which you are holding in your hands. Statistics is only saying something about a huge number of chips. Keep in mind that it does not give any guarantee for an indidivual chip. Your chip can easily exceed any sigma of the standard deviation without violating the laws of statistics. So I would be very careful when assuming any narrow set limits "postulated" by statistics.

    Kai

  • +1 in reply to kai klaas69
    TI__Prodigy 60 points

    Dear Kai san

    Thank you for your detailed information.

    I understood what you mean.

    I will be carful about maximum spec via customer communication.

    Thanks

    Regards

    Yosuke Tanaka