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LDC1312: Resolution RCOUNT and Divider Code (Fref)

Filipe Pereira
Prodigy 165 points
Part Number: LDC1312

Hello Everyone,

I´m a little bit confused regarding the resolution for my application. I have a inductive sensor which has a coil with L = 10,3 mH and the sensor frequency is about 25 KHz.  I have read in SNOA945 that in lower sensor frequencies the Fref should also be lower to increase the resolution. In Table 4 SNOA945, for example, the Fsensor is 980 KHz and Fref is 4 MHz, that is the best resolution. I don´t know how to find the best Fref for my application. Do you have any suggestion to calculate the Fref?  In the same Table 4 (SNOA945) there is a column "Output Code", what is that means? I could not find it.

Thank you very much

Best Regards

  • 0
    TI__Genius 14270 points
    Hello Filipe,

    Setting the ratio of fin/fref to just under 0.25 provides the best resolution. Keep in mind that the ratio of fin/fref should not exceed 0.25, otherwise quantization errors can occur which will decrease the resolution.

    Remember, the lower fref is, the longer the conversion time. Sometimes it may be better to average multiple conversions from a higher sample rate than to decrease the frequency of fref.

    The Output code is the data output that the LDC131x puts in the DATAx registers.

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Prodigy 165 points

    Hello Chris,

    Thank you very much for your answer.

    So a good Fin/Fref is 0.25 due to quantization. I agree with you, when the Fref is too low the sample time is too high and the system is also too low. The best way to change it is make a kind of average. 

    Thank you again