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LMP90080-Q1: supports NTC sensor?

Alen Barisic
Intellectual 1300 points
Part Number: LMP90080-Q1
Other Parts Discussed in Thread: ADS1148, ADS114S08

Hello,

Could you please let me know if the multichannel AFE LMP90080-Q1 can be used for other temperature sensors types such as NTC (which is not mentioned in the datasheet).

Do we have any any AFE with SAR ADC inbuilt?

Thanks,

Alen

  • 0
    TI__Mastermind 40261 points

    Hi Alen,

    Do you need a -Q1 rated device for your application? We have other, newer ADC options available if you do not.

    Also, from your last question, do you have a need for a SAR over a delta-sigma ADC? Typically we see engineers using delta-sigma ADCs for temperature sensor measurements such as NTCs, since these sensing parameters tend to change very slowly and require higher precision.

    Let me know and we can hopefully identify the correct device for your application.

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Intellectual 1300 points

    Hi Bryan,

    thank you for the great support!

    Q1 qualification is not required for our applications. Could you please point me to these new ADC options?

    This is to interface temperature sensors (PT100, KTY84-130, NTC10k/NTC30k). We would want to change between sensor types with only software update and no HW changes. Delta Sigma is also fine (no speed requirements). 12 bit resolution is good enough if a SAR ADC.

    Thanks,

    Alen

  • +1 in reply to Alen Barisic
    TI__Mastermind 40261 points

    Hi Alen,

    Thanks for the feedback.

    You can use a device like the ADS114S08 then, which is the next generation version of the ADS1148.

    The ADS114S08 has more analog input channels compared to the ADS1148, so you should be able to measure the maximum amount of NTCs with the ADS114S08 without requiring hardware changes.

    Also, similar to the ADS1148, the ADS114S08 has a REFOUT pin that can be used to bias the NTC resistor divider. However, the ADS114S08 internal VREF is a 2.5V reference (compared to 2.048V on the ADS1148), so you can get a little more dynamic range out of the resistor divider using the ADS114S08.

    The ADS114S08 also has a PGA bypass feature if you want to measure ground-referenced (single-ended) signals. The ADS1148 did not have this feature either.

    I would check out this ADC to see if it meets the needs of your application. Let me know if you have any further questions.

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Intellectual 1300 points

    Hi Byan,

    We want to connect one of the sensor from NTC10k or NTC30k or KTX84-130 or PT100 or PT1000 to the same channel of the ADC.

    And excite the sensor from controllable excitation current from ADC according to the sensor connected and also with software control, change the gain to have the temperature measurement.

    Is this possible with ADS1148 as we don’t need more number of channels?

    Regards,

    Alen

  • 0 in reply to Alen Barisic
    TI__Mastermind 40261 points

    Hi Alen,

    You should be able to come up with a configuration that can measure all of those sensors types with the ADS114S08. The main challenge I can see will be if your input terminals are limited. For example, if you need to connect the NTC and RTD to the same input terminals, you might need some kind of external switch to turn on/off certain parts of the circuit, including the bias resistor for the NTC (which cannot be in the IDAC path if the RTD is connected for example). If you want to provide more information about how the NTC and RTD will be physically connected to the board e.g. a 4-terminal block, then I can try to help come up with an input scheme. Or, if this all makes sense and you can take it from here, I will then point you to some useful collateral: thermocouple and RTD cookbooks

    These documents contain a wealth of information about these analog sensor types as well as all common configurations and how they are connected to a delta-sigma ADC. Note that the TC includes some information about NTC configurations, as NTCs can be used for cold junction compensation in TC measurements.

    We also have temp sensing firmware that is applicable to the ADS114S08 (not the ADS1148): https://www.ti.com/tool/ADC-TEMP-SENSOR-FW. This FW contains the configuration settings for the ADS114S08 when measuring the most common analog temp sensors. It also includes the linearization routine e.g. look-up tables, polynomials, etc. for these same sensors. This FW is not currently applicable to the ADS1148.

    I would encourage you to review this collateral as it should make you design easier to implement.

    -Bryan