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LDC1000: Question about changing the output rate

Joao Bastos
Prodigy 90 points

Part Number: LDC1000

Hi,

I am building a custom application using an LDC1000 device. The idea is to measure the rotation speed of a metallic material. The application works quite well, however. I have added a guard for checking the status register of the LDC1000 to make sure the proximity data is ready before we read it.

We have now increased the frequency at which we read the Proximity registers and have notice an increase in the number of data not being read due to NOT BEING READY.

I checked the datasheet, where it states the Output Rate is a function of the defined RESPONSE_TIME and Sensor Frequency.

I am a bit puzled with the whole information, so if you could help me I would be very thankful.

  • Is this the Sensor Frequency based on the Watchdog Timer? Why would this change the output rate? If not, then what frequency am  I supposed to tune.
  • We do not use an external clock as we do not need to measure inductance. Does this impact the Sensor Frequency for the output rate? If not, then what am I really changing?

Thank you in advance

  • 0
    TI__Genius 17440 points

    Hello Joao,

    The LDC1000 will no longer be available for purchase next year. You should use a different inductive sensing device. The closest match for the LDC1000 is the LDC1101, which also performs both Rp and L sensing. If you encounter similar issues with the LDC1101 or this device does not work for your application, please feel free to post again and we'd be happy to help.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 90 points

    Hi Kirstin, thanks for the reply.

    That is clear to me. I had the impression an LDC1001 was also to be release with similar functionalities to the LDC1000, but still if we are to make an application exploratory design, the problem is kept. So is there an answer to this question? 

    We do not need and L sensing, simply Rp is sufficient. What we have is a lot of data that is not ready when we want to sample it and would like to know how to increase the output sample rate of the LDC1000/LDC1001.

    Kind regards

  • 0 in reply to Joao Bastos
    TI__Genius 17440 points

    Hi Joao,

    We strongly recommend using the LDC1101, which supports Rp sensing. The LDC1101 has the following benefits over the LDC1000:

    • cheaper
    • 2x faster SPI and 2x faster sample rate
    • shutdown mode
    • lower current
    • deglitch filter

    For both the LDC1000 and the LDC1101, the Rp measurement functions in this way:

    Just to clarify, the sensor frequency is the resonant frequency of the LC tank sensor. The Rp_min/Rp_max settings determine the current drive applied to the sensor. First, a high current is applied until the sensor oscillation reaches a peak amplitude. Then, a lower current is applied until the sensor oscillation reaches a minimum amplitude. The Rp measurement is a ratio of the time that each current is applied. For higher sensor frequencies, this process can be completed faster, which increases the sample rate. An easy way to increase the sensor frequency is to decrease the fixed capacitance value of the LC tank.

    The external reference clock only influences the sample rate if you are using L sensing.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 90 points

    Hi Kristin,

    Thank you so much for you reply. It is really helpful! This is exactly what I was looking for.

    With respect to the LDC1101, we make use of simultaneous access to the comparator signal on the INTB pin as well as ready the data in the LDC via SPI. It seems to me that this simultaneous use cannot be done on the LDC1101 because the SD0 and INTB signals are on the pin, right?

  • 0 in reply to Joao Bastos
    TI__Genius 17440 points

    Hello Joao,

    That is correct. Unfortunately because SDO and INTB are a shared pin, you cannot use those functions simultaneously.

    Best Regards,