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Same behavior in different Rp range

Varban Metodiev
Intellectual 690 points

Hello Team (Evgeny, Chris),

I have tested the LDC1000 with the following configuration:

470nF parallel capacitor in the LC tank.

100nF CFB capacitor - this was the value that caused 1-volt pulsation on the CFB pin.

I configured the RPx registers with the following values: (RpMAX = 1A,  RpMIN = 3C) and one unit above (RpMAX = 1B,  RpMIN = 3D) - what I got was one and the same value in the Proximity MSB register.

When going one unit above/beneath that values, the chip does not generate Data Ready interrupt on the interrupt pin. Also, the CFB pin goes in 5V, stable line with no oscillation.

This scenario  was repeated on another LDC1000 IC, located on a different place on the PCB - and there was no change in the behavior with the mentioned configurations.


Here are some shots (RpMAX = 1A,  RpMIN = 3C):


And the upper one unit configuration (RpMAX = 1B,  RpMIN = 3D):



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So, my questions are the following:
1) Is this a normal behavior of the LDC1000?
2) Should one of the two ranges be more stable at temperature changes?

Kind regards,

Varban

  • 0
    TI__Genius 14270 points

    Hello Varban,

    From my calculations, the inductance of the sensor is ~100uH, is that correct? Make sure that the min sensor frequency in register address 0x03 is set correctly. The sensor RP may also be too low; please try using lower resistance settings for RPMIN. Also, it is not recommended to set RPMIN and RPMAX less than 2 resistance settings apart. Please make sure that the oscillation amplitude on the CFB pin is measured over 20-50 cycles of the sensor frequency.

    The scope plots are helpful, but I would like to see the units on the in the capture; also, some of the plots were a bit blurry and hard to interpret.


    Regards,

    ChrisO