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LDC1101: Meaning of time constants

marto marti
Prodigy 30 points
Part Number: LDC1101

Hello.

Currently, I'm thinkering with a LDC1101 and while reading the datasheet, I can't really understand the function of the TC1 and TC2 registers. They seem to be setting some sort of filter cutoff frequency, but what I can't understand is what signal is this filter affecting.

Is this a filter applied to the measurements or to the LC tank driver itself? Will impropper settings affect the oscillation of the sensor or just the measurement results?

I'm asking because when testing the LDC1101 with the default parameters, the measurements (at least of RP) are quite noisy. So I would like to undestand how to configure those parameters to get better readings.

  • 0
    TI__Mastermind 23810 points

    The advice given in the datasheet about how to choose the time constants should help you select the best values.

    In general, Rp measurements are noisier than the high resolution inductance measurement. If it is possible to use the L measurement, I recommend switching to that.

    What is your application?

  • 0 in reply to Clancy Soehren
    Prodigy 30 points

    The application is a small displacement sensor for rotating machinery vibration analysis.

    I've tried to read the L_DATA registers but the value stays on zero no matter the position of the test target.

    On the other hand, the adapter board I made is connected to the DSP with longish wires, so noise from the reference clock and the communication bus is coupling into the oscillator output (confirmed by probing with a scope).

    Later I will design a new board with better decoupling, ground plane, and maybe a local oscillator instead of the PWM. However it seems strange to me that the L reading outputs always 0.

  • 0 in reply to marto marti
    TI__Mastermind 23810 points

    It is strange that you are always reading 0... Are you seeing the LC oscillation signal when probing INA and INB?

    Are you able to read other registers correctly?

  • 0 in reply to Clancy Soehren
    TI__Mastermind 23810 points

    Please let us know if you still need help.