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FDC2112: Understanding Datasheet

Pavel Shageev
Prodigy 10 points
Part Number: FDC2112


Hi,

In datasheet of FDC2112, on page 14, table 1 says that the valid fINx range is < Fref / 4. (As I understand it, fIN is the frequency of LC tank, divided by CHx_FIN_SEL)

But section 10.2.3.2 on page 42 says: The design constraint for fREF0 is > 4 x fSENSOR. And throughout this example, this relation is implied. (Sensor frequency in this example is 5.15 MHz, CH0_FIN_SEL set to b10 and "To satisfy this constraint, fREF0 must be greater than 20.6MHz")

I see this as a discrepancy. How right? fIN < 4 x fREF  OR fSENSOR < 4 x fREF?

Regards.

  • 0
    TI__Genius 17440 points

    Hello Pavel,

    I agree that there is a discrepancy between table 1 and section 10.2.3.2. F_IN < 4 x F_REF is correct. However, note that this equation is just for the minimum frequency, and using a reference frequency higher than this will improve the resolution. If you follow F_sensor < 4 x F_REF then the F_IN < 4 x F_REF inequality will always be met, and for higher values of CHx_FIN_SEL the resolution will be improved.

    Best Regards,