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DP83848M: Crystal Drive Level

Bernd Sprenger
Intellectual 330 points
Part Number: DP83848M
Other Parts Discussed in Thread: TIDA-00207

Hello,

I am using the DP83488 in a design and I am currently selecting the crystal. In order to verify that the selected crystal operates in its permitable power range, I need to calculate the crystal power dissipation value. For that I would need to know the voltage at which the crystal oscillator circuit operates (amplitude of the oscillation).

      Pxtal = 0.5 ESR (2*π*frequency*CLoad*VDDS_OSC)²

If I take the crystal and components used in the TIDA-00207 I get for a voltage of 1.8V a drive level of 740uW, which is outside of the specification of the used crystal.

(CTS 445I23D25M00000 => ESR=40R; C0=5.0pF; CLoad=18pF; 300uW Max)

What is the crystal oscillator circuit voltage, resp. what is the amplitude of the oscillation?

Thanks a lot for your help,

have a nice day,

Bernd

  • 0
    TI__Expert 5425 points

    Hi Bernd,

    The amplitude of the oscillation is something that is not characterized. You will have to use a series resistor on the XO pin to reduce the current driven into the crystal. You can try it on your system and measure how much the voltage is reduced. To start off, try using a 330 ohm resistor and increase the value if the reduction is not enough. However, I would not exceed 1.5kohm as it could cause bit error rate issues. After adding the resistor, I would suggest performing a system level test to make sure everything is ok.

    Regards,

    Adrian Kam