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Why is the Measured Frequency influenced by the RP min and RP max parameters(LDC1000)

Ronny Vrijelinck
Prodigy 50 points
Other Parts Discussed in Thread: LDC1000EVM

Hello,

 I am experimenting with the LDC1000EVM to see if it's usable for our application.

 We use a coil of 680µH with a ferrite potcore and a capacitor of 1nF, serie resistance of the coil is 6 Ohm.

 I changed the CFB Filter capacitor to 680pF to get a amplitude of about 1V PP on the CFB cap

 I measured a RP of about 18KOhm.

 What i don't understand is that the measured resonance Frequency value is influenced by the RPmin and RPMax setting

 Can somebody explain this?

 I also see that the signal on the LC resonance circuit is not a full sinewave, at the bottom the sinewave is cutOff, is this normal or should the signal be a full sine wave?

  • 0
    TI__Genius 9300 points

    Hello,

    Indeed, in an ideal world, you would not see any difference. Unfortunately, electronics is not ideal with non-linearities, propagation delays etc.

    Nonetheless, it's not important in applications - the Rp settings are not changed in absolute majority once they are set, and the variance is smaller than the cap precision anyway.


    Half-sine wave on IN pin is fine.