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LDC1101: LDC DRDY Timing for LDC1101 or LDC1001

Michael9q
Intellectual 565 points
Part Number: LDC1101
Other Parts Discussed in Thread: LDC1001, , TDC7200

Hello there,

I would like to compare here LDC1101 and LDC1001 in LDC DRDY Timing measurement.
All based on SNOA941A  App Report and LDCs manuals SNOSD01D and SNVSBF7.

I want to use LDC1x01 for high resolution and fast sample rate (10 kSPS).
I have tested LDC1101 with 15 mm dia coil which has resolution 2 um with RCOUNT 5A (90 usec).
Base on this experiment I believe that increasing timing resolution (1/16e6 = 62ns resp. 1/32e6 = 31.125ns based on SNOA941a header 3) will increase also resolution of the sensor.

Important aspects I am aware of:
A1: LDC1001 can use only 8 MHz reference oscillator compared to LDC1101 with 16 MHz which I do not think it is important in case of LDC DRDY Timing measurement since LDC works as even counter.
A2: LDC1001 can drive sensors 5kHz-5MHz compared to LDC1101 0.5-10MHz. Depending on application an appropriate LC tank may be chosen.
A3: LDC1001 has compared to LDC1101 INTB functionality on special pin (16) which gives advantage for MCU using it instead of getting it from SDO as on LDC1101.
A4: Sensor amplitude for LDC1101 is 1.2Vpp compared to 1-4 Vpp by LDC1001.
A5: LDC1101 is approximately half the price.

Q1: What LDC can give higher performance in DRDY timing mode? (if not comparable based on A1)
Q2: LDC1001 should be capable of driving bigger inductor since it can drive smaller Rp (800Ω --> 4000kΩ) compared to 1.25kΩ to 90kΩ by LDC1101, correct?
Q3: Is the LC tank driver stronger by LDC1001? Is it important?
Q4: If DRDY Timing measurement is set, LDC1101 set in LHR mode will not measure any Rp correct? (The measurement stability is not influenced)
Q5: Is the sample rate achievable in this measuring configuration same for both?

Thank you very much for your answers.

Best Regards,

Michael

  • 0
    TI__Mastermind 34285 points

    Michael,

    Thank you for your inquiry and your interest in TI products.
    I will have answers for your questions by COB on Friday.

    Regards,
    John

  • +1 in reply to John Miller - Sensing
    TI__Mastermind 34285 points

    Michael,

    Answers for your Q1-Q3 are below.  I will have answers for Q4 & Q5 by Tuesday of next week.

    Q1: What LDC can give higher performance in DRDY timing mode? (if not comparable based on A1)
           Which metric is of greatest importance for your application?
    Q2: LDC1001 should be capable of driving bigger inductor since it can drive smaller Rp (800Ω --> 4000kΩ) compared to 1.25kΩ to 90kΩ by LDC1101, correct?
           The LDC1101 should be able to drive a lower Q circuit. All other things being equal it may translate to larger inductor, but not necessarily so.
    Q3: Is the LC tank driver stronger by LDC1001? Is it important?
           The data sheets show the LDC110 sensor max current drive is 0.6mA, and the LDC1001 sensor max current is 2Vp/798 = 2.5mA.
           Based on that, it seems the LDC1001 may have the strongest drive capability.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 565 points

    Hi John,

    Thanks for answers.

    Q1: Based on supported reference clock LDC1101 has higher resolution of frequency for same sample rate than LDC1001. I wanted to confirm that LDC1101 and LDC1001 will have same resolution in DRDY mode since this measurement method is rather a frequency counter than measurement. Actual measurement is processed by TDC7200. 

    If not, which LDC works with higher resolution for same sample rate in DRDY mode?

    Thanks,

    Best Regards,

    Michael 

  • 0 in reply to Michael9q
    TI__Mastermind 34285 points

    Michael,

    I will have an answer to your question about DRDY performance tomorrow.

    Regards,
    John

  • +1 in reply to John Miller - Sensing
    TI__Mastermind 34285 points

    Michael,

    The LDC1101 in LHR mode will have higher resolution than the LDC1001 due to the higher reference frequency. 
    In DRDY mode, it seems the LDC1101 is still gives better resolution since it still supports LHR mode. 

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 565 points

    John,

    yes I agree that in LHR mode LDC1101 has higher resolution than LDC1001 based on reference frequency limits. 

    What I am not sure about, in DRDY mode, LDC1101 uses only L+Rp measurement not LHR measurement correct?

    In LHR mode it has constant conversion time independent from sensor oscillation set by RCOUNT value. Timestamp between data ready interrupt are constant no matter what LDC measures. 

    I believe that for DRDY mode it should be set to L + Rp mode and configured to LOPTIMAL 0x05 - 1 so it measures only L. Then it works as event counter (event is rise edge of frequency).

    Even with this approach, does LDC1101 have higher resolution?

    Please confirm that this is correct otherwise how can be used DRDY mode with LHR mode?

    Thank you,

    Michael 

  • +1 in reply to Michael9q
    TI__Mastermind 34285 points

    Miacheal,

    According to the data sheet, L + Rp mode measuring only L will give a more stable measurement, but necessarily a more precise one (sec. 8.4.5).
    You can use DRDY reporting in LHR mode, and that should get the best resolution; section 9.1.14/15 of the data sheet gives some details and caveats.

    Tables 13 and 37 of the data sheet shows LHR mode with DRDY reporting can be invoked via the INTB_MODE register.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 565 points

    Hi John,

    I agree with point 1, LDC should be set for optimal L measurement described in section 8.4.5:

    ALT_CONFIG.LOPTIMAL(register 0x05-bit0) = 1
    D_CONFIG.DOK_REPORT (register 0x0C-bit0) = 1

    It is still unclear to me how can DRDY reporting work in LHR mode. We have used INTB interrupt on SDO in LHR mode. It sends interrupt once the the conversion time is completed for LHR data. This LHR-DRDY is independent from sensor frequency, it is function of RCOUNT. It cannot be used for sensor frequency measurement. 

    While using LHR mode, can LDC1101 also work as event counter and assert of RPL-DRDY which is then used for frequency calculation?

    Thanks,

    Michael

  • 0 in reply to Michael9q
    TI__Mastermind 34285 points

    Michael,

    Using the LHR mode would require a supporting MCU w/code to do the event counting.

    L + Rp mode will support event counting, but perhaps provide a less precise L measurement.
    LHR mode will give a more precise L measurement, but event counting will have to take place outside the device.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Intellectual 565 points

    John,

    this is not clear to me.

    How can LHR mode be used for for frequency measurement without reading LHR data? What event counting do you mean?

    Thanks,

    Michael

  • 0 in reply to John Miller - Sensing
    Intellectual 565 points

    I also found this comparison table in snosd01d datasheet for LDC1101:

    Switch output on SDO/INTB. Apparently it is not available for LHR mode. What does it correspond to?

    Thanks

  • 0 in reply to Michael9q
    TI__Mastermind 34285 points

    Michael,

    I'm not sure I completely understand your last question, but the device block diagram shows a threshold detection/switching available for SDO only on the Rp+L mode, and not the LHR mode. 

    Regards,
    John

  • +1 in reply to John Miller - Sensing
    Intellectual 565 points

    Hi John,

    I will use Rp + L mode without Rp measurement for optimum L measurement. By TDC7200 I will measure timestamps between DRDY assertion set by RESPONSE TIME hoping for best possible frequency resolution.

    If there is any better way for measurement of frequency in LHR mode with TDC7200 in DRDY mode, please share it with me here.

    Thanks for all the help.

    Best Regards,

    Michael

  • 0 in reply to Michael9q
    TI__Mastermind 34285 points

    It sounds like you have chosen the best option for your requirements.
    Please let me know if you have any questions.

  • 0 in reply to John Miller - Sensing
    Intellectual 565 points

    John,

    I actually found one more issue. 

    What does response time corresponds to (latency between measurement and DRDY assertion)? In 7.5 Electrical Characteristics of SNOSD01D It says that minimum response time (RP+L mode) is 192/Fsensor but maximum sample rate is (3xFsensor)/ResponseTime, where minimum Response Time is 192.

    What does it mean that for response time it is 192/Fsensor and for sample rate (conversion time) it is 192/3x Fsensor?

    Thank you,

    Michael

  • 0 in reply to Michael9q
    TI__Mastermind 34285 points

    Michael,

    Would you please do us a favor?
    Would you please close this thread and open a new one with this latest issue?
    It makes it easier for other E2E users to search threads for solutions, and it helps our thread tracking as well. 

    Regards,
    John