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Original question:

XTR111 Design

XTR111: XTR111 error sources

Emilien COULAUD
Prodigy 230 points

Part Number: XTR111

Hello,

Question 1 : span error versus gain error definitions:

In XTR111 datasheet :

  • page 3/32 a  "Span Error Iout/Iset" is specified 
  • page 7/32 figure 11 and 12 : curves of "gain error"

What is the difference between "gain error"  and "span error" for the XTR111?

Question 2 : phase delay:

In XTR111 datasheet page 6/32 figure 3, there are 3 curves of gain versus frequency.

But we didn't find spécifications of phase delay.

In our application, we need several voltage/current conversion channels.

Phase delays mismatch between channel is an important parameter for this application.

Thank you for your attention,

Best regards,

Emilien

  • 0
    Guru 140200 points
    Hi Emilien,

    the "span" is explained in the footnote (3) of page 3 of datasheet. And the "gain" is explained in figure 3 of datasheet.

    Kai
  • 0
    TI__Mastermind 23050 points

    Hi Emilien,

    The gain as shown in figure 3, is the ratio of the load voltage to the input voltage as in traditional voltage amplifiers. Span is the change in output current resulting from a full-scale change in input voltage and the error is given as deviation in the ratio of Iout/Iset from the ideal value of 10. It is effectively a gain error as well and if you look at figure 12 you can see the typical value of 5ppm/C correlates with what is shown in the table. The typical value of the gain error distribution in figure 8 also matches the typical value of the span error.

    We do not have any data on the phase characteristics of the device, but you can see from the the gain vs frequency curve that there is a dominant pole at about 1MHz, and so you will start to see a change in phase at around 100kHz. If you are operating on the lower end of the spectrum, then you shouldn't have to worry about phase variations. 

  • 0 in reply to Zak Kaye
    Prodigy 230 points

    Hi Zak,

    Thank you for your suuport,

    Gain error / span error: that is what I supposed that "gain error" and "span error" terms designates the same phenomenon

    Phase: as gain curve look like a 2nd order low pass fiter. Approximating phase by one of a 2nd order low pass filter  is a good approximation or not?

    What  "bounds" for cut off frequencies variation , on full operating temperature range [-55;+125]°C),

    can i take into account? 

     

    Best regards,

    Emilien

  • 0 in reply to Emilien COULAUD
    Guru 140200 points

    Hi Emilien,

    have you read the section "dynamic performance" of datasheet? You might want to add some low pass filtering to the output. Then you will have a lower bandwidth and a higher phase shift.

    What is your desired signal bandwidth?

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 23050 points
    Hi Emilien,

    You are correct, it is a second order response, but if you are operating on the lower end of the spectrum than this still shouldn't be an issue. I think you are going to run into more phase variation based on the length of cable you use, the transistor you select, and whatever external low pass filter you implement. The XTR itself should not contribute much unless you operate close to its bandwidth limit. Generally for parameters like this we use +/-30% as a conservative estimate for how much the device might vary with process variations. The temperature variation of the cutoff frequency is not something that we characterize though.
  • 0 in reply to Zak Kaye
    Prodigy 230 points

    Hello,

    Thank you !

    Best Regards,

    Emilien