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LDC1000 operation check, and about connection condenser between CFA-CFB.

Nobuhiro Haruta
Prodigy 230 points


Hello,All.

I have some questions about  LDC1000 operation check, and about connection condenser between CFA-CFB.

Customer decides the design fixed number now.

Therefore he must explain design contents in end user. Therefore, he is curious about the following contents.

LDC1000 is new function IC. Thus, he has need to explain the grounds that he adopt it and examined for his office and END customer. And he wants to decide the fixed number early.

About connection condenser between CFA-CFB. This will decide capacity of oscillating C of approximately 1V by explanation of datasheet 22page No. 4. In addition, follows are written down in datasheet 22page. The traces connecting CFA and CFB to the capacitor should be as short as possible to minimize any parasitics.

１．Why will it be necessary to make 1V?

２．When it is lowered than 1V, what will happen? (A condition: In the case of a smoothed wave pattern)

３．When it becomes bigger than 1V, what will happen?

Best Regards,

  • 0
    TI__Genius 14270 points
    Hello Haruta-san,

    Thank you for your interest in the LDC1000. To answer your questions:

    1) The 1V is to maintain signal fidelity (lower reduces measurement fidelity), while larger amplitudes pose a risk of over-ranging some internal device nodes.
    2) Too low and the conversion results will have higher standard deviation.
    3) Too large a CFB voltage can result in over-ranging some internal device nodes; this can result in incorrect conversion results.

    Please keep in mind that the appropriate time-scale to monitor for the CFB pin voltage envelope is approx. 100x the sensor frequency. For example, with a 1MHz sensor frequency, the time scale to look for the 1V amplitude would be 100*(1/1MHz) -> 100us.

    Regards,

    ChrisO