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XTR111: some question regarding the datasheet

Noriyuki Takahashi
Genius 9245 points
Part Number: XTR111

Hi team,

I have questions regarding XTR111 datasheet.

1. Looking at Figure 6, there are several spikes between 10kHz and 100kHz. Why these spikes are generated?

2. At the note (4) P.2, is following understanding correct?

+25mA means sink current. -50mA source means source current.

Regards,

Noriyuki Takahashi 

  • 0
    TI__Expert 5830 points
    Hello Noriyuki Takahashi,

    The current mirror is a chopping topology which is why there are spurs in the noise spectral density between 10kHz and 100kHz. Within the application section on figure 40 and 41 show ways to filter the output noise on both the transmit and receive sides. Note (4) talks about the absolute maximum rating for current through the IS pin. The +25mA pertains to sourcing current and -50mA pertains to sinking current.

    Best regards,

    Errol Leon
    Texas Instruments
    Precision Amplifiers Application Engineer
  • 0 in reply to Errol Leon6
    TI__Genius 9245 points

    Hi, Leon

    Here is additional questions regarding chopping technology and the section of DYNAMIC PERFORMANCE p.15.

    1. What is chopping topology for? 

    2. Is the spike in the figure 39 come from the chopping?

    3. It seems that there is still fluctuation in the figure 40&41, even if using filtering. The fluctuation comes from also the chopping?

    4. I am not sure yet the following explanation in P.15. Could you explain this in detail? Especially, what are t"he dynamic matching of multiple individual current sources" and "settling to full resolution"? 

    "The accuracy of the current mirror relies on the dynamic matching of multiple individual current sources. Settling to full resolution may require a complete cycle lasting around 100μs. Figure 39 shows an example of the ripple generated from the individual current source values that average to the specified accuracy over the full cycle."

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Expert 5830 points

    Hello Noriyuki Takahashi,

    1. What is chopping topology for?

    • It is used to accurately mirror the current through the internal FET by correct current offset. 

    2. Is the spike in the figure 39 come from the chopping?

    • That is correct.

    3. It seems that there is still fluctuation in the figure 40&41, even if using filtering. The fluctuation comes from also the chopping?

    • That is correct. On the receiver side (Figure 41) the fluctuation is minimized roughly an order of magnitude by the passive low pass filter (Scaling changed on y-axis to 5mV/div). 

    4. I am not sure yet the following explanation in P.15. Could you explain this in detail? Especially, what are t"he dynamic matching of multiple individual current sources" and "settling to full resolution"? 

    "The accuracy of the current mirror relies on the dynamic matching of multiple individual current sources. Settling to full resolution may require a complete cycle lasting around 100μs. Figure 39 shows an example of the ripple generated from the individual current source values that average to the specified accuracy over the full cycle."

    • If Vin of XTR111 changes the gate voltage of the internal FET will change thereby causing the current Iset to change.  The current mirror will take time to adjust the output current to the correct current value which is 100us. Figure 36 shows the XTR111's functional block diagram that shows this.

    Best regards,

    Errol Leon

    Texas Instruments

    Precision Amplifiers Application Engineer