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XTR300: determine Cc, C4 and Rc values

Ioana Marica-Bercu
Prodigy 25 points
Part Number: XTR300
Other Parts Discussed in Thread: XTR305

Tool/software:

Hello, 

I am currently dealing with the XTR305 chip and I am trying to find a good balance between the values of the Cc, C4 and Rc (designators from DS,Figure 40). The challenge is achieving a max. phase delay of -3 degrees at 300Hz for both I and V mode, while varying the Rload from 50 to 500 in I-mode. As of now by using the TINA simulations it seems that the values that I found either amplify the signal at higher frequencies for small load resistance in I mode or achieve a phase delay higher than 3 degrees at 300Hz in V mode. Is there a way to achieve a filtering behaviour while keeping the phase delay within the required limits? Gladly I can provide more details if needed. Thank you in advance.

  • 0
    TI__Mastermind 28340 points

    Hi Ioana,

    I'd like to better understand your application. Are you saying that you will want to actively change between I and V modes? You don't just need to have several variants of this circuit where one will always be designed with current mode in mind and the other will always do voltage mode? 

    What's the Rload for the voltage mode circuit? 

    Best Regards, 

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    Prodigy 25 points

    Hello Robert,

    thank you for your reply.

    That is correct, i am intending to actively change between the I and V modes on the same circuit. Not toggle, but rather set the circuit once to either I or V mode. For Rload in V Mode i set between 50k and 900k. However I could not notice any significant change in the output signal in V mode when varying the resistance between these limits - I assumed therefore little or no influence. In I mode nonetheless the response changes when varying the resistance between 50 and 500 Ohms and the 50Ohm results are rather unsatisfying.

    Best regards,

    Ioana

  • +1 in reply to Ioana Marica-Bercu
    TI__Mastermind 28340 points

    Hello Ioana,

    I should have also asked for your simulation circuits. Can you please share that with me? 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    TI__Mastermind 28340 points

    Hi Ioana,

    Lowering the C4 capacitance should help. Try C4 = 24nF. It provides a drop of 2.44 degrees. Having a 20% capacitance tolerance will bring the delay to 2.7 degrees, so there's some margin from your 3 degree limit. 

    Decreasing it further would also work but at 50 ohms you start to see signs of instability so you'd likely have to increase the Rc resistor. 

    Best Regards, 

    Robert Clifton