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Damping resistor calculating formula of ADV7282A

Hi ADI expert,

Might you please help to check what's the definition or calculation equation of total Capacitance?


And it mentioned each side, do we have to divided by two? 

Thank you!!


Parents Reply
  • Hi,

    Please find the below comments,

      For example, if the external capacitor is 12pF, device pin capacitance is 4pF and PCB is estimated at 2pF, the the value for cell B5 would be 18pF, right ?

        We can calculate the capacitance by referring AN-1260 application note, For example,

        C1 = C2 = 2(Cload - Cstray) - Cpg

        Assume Cstray = 2-3pF, depends on board traces

        Assume Cpg = 4pf, pin capacitance.

    C2 & C3 are dependent on the load capacitance specified in the crystal data sheet.  As an example a Golledage MA01377 has a load capacitance of 30pF so C2 = C3 = 2 * (30 - 2) - 4 = 52pF, closest real cap. value would be 47pF. These caps adjust the impedance the crystal drivers see to make sure the crystal will oscillate.

       Below we have attached the crystal that was used on our evaluation board,however we can use other crystals as long as we re-calculate the load capacitors based on the following application note.


    Also, are the voltage values in cells E20, E21, F20, F21 meant to be edited? 

         No, the voltage values can't be edited & you will get the voltage value depending upon the value that you are feeding on the calculator tool of section 1

        Please note the purpose of this damping resistor is to limit the current flowing through the XTAL and to limit the voltage across the XTAL amplifier. To define the appropriate value of the damping resistor RDAMP (see the Typical Circuit Connections section), consult the accompanying calculator tool at ADV7182A/ADV728xA Resistor Tool (Rev. A)

    Are these values defined by the ADV728x or for the crystal?

          E20, E21, F20, F21 values are defined for the crystal.



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