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The capacitance of the capacitor of the RI-STU-MRD2

M.H
Genius 5960 points
Other Parts Discussed in Thread: RI-STU-MRD2

Hi,

Than RI-STU-MRD2 Reference Guide (SCBU049) 5.2 Adapting the Inductance Range (19 Section), there is described as possible tuning due to the capacitor added.

Capacity of the internal capacitor of RI-STU-MRD2 Although there is described as 30nF,
Is there a variation in this value?

Best Regards,

hamada

  • 0
    TI__Guru* 91206 points

    the populated value of the cap is 30nF, as the intended value of the antenna coil for connection to the microreader is 47uH (with a Q of <20) and the frequency of operation is intended to be ~134.2kHz. Since fc = 1/2pi*(sqrt(L*C)), 134.1kHz = 1/2pi * (sqrt(47uH*30nF)). This is close enough. 

    if your antenna is outside the range of 46-48uH, you can adapt it to work with microreader by adding external cap (either in series or parallel), depending on if its lower or higher than the specified value. 

    if its lower than 46.1uH, you can add in parallel (between pins 16 and 17) and the formula to use is: 

    Cext = Ctot - 30nF

    if its higher than 47.9uH, you can add in series (between pin 19 and  the antenna coil) and the formula to use is: 

    1/Cext = 1/Ctot - 1/30nF

    with total resonance capacity formula being: Ctot = 1/(4pi (squared) * Lant * f(squared))

    is it clear now? 

  • 0 in reply to Josh Wyatt
    TI__Guru* 91206 points
    Hamada -
    also, the tolerance of the capacitors you are asking about which will make the 30nF (in positions C35/C38) are +/-5% (C0G)
  • 0 in reply to Josh Wyatt
    Genius 5960 points
    Hi, Josh.

    Detailed description, thank you.


    >also, the tolerance of the capacitors you are asking about which will make the 30nF (in positions C35/C38) are +/-5% (C0G)

    C35 / C38, where do you have pointed to as?

    Best Regards,

    hamada
  • 0 in reply to M.H
    TI__Guru* 91206 points

    Hamada - 

    please see picture below for the locations of the tuning caps on the board.