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LMT8x: What kinds of ADC is recommended?

Noriyuki Takahashi
Genius 9245 points
Other Parts Discussed in Thread: LMT87, LMT70

Hi team

I have questions regarding LMT8x.

- When the ADC's input range is upto 3.3V, which LMT8x series is recommended? and why?

- In general, how much of resolution of ADC is enough for LMT8x series?

Regards,

Noriyuki Takahashi

 

  • 0
    TI__Expert 6475 points

    Noriyuki,

    It really depends on the operating temperature range that you're interested in since there is a gain trade off between the LMT8x devices.

    Given the same supply voltage, the higher the gain the smaller the operating temperature range you can have.  Ideally, you would want to maximize the dynamic range so use the highest gain allowable for your temperature range of interest.

    The first page of the datasheet will tell you the output voltage range of the device vs temperature.  For example, at -50oC the LMT87 device outputs ~3.3V (see Table 1 also).  However, you will need to supply LMT87 with at least 3.5V to be able to operate down at -50oC due to the headroom requirement, see Figure 2 of datasheet.  If you supply the LMT87 with 3.3V then the lowest temperature that you can measure is ~ -30oC.

    I would recommend a 12-bit ADC.  I would recommend looking at the LMT70 EVM as an example. The reference has a significant impact on the system accuracy so you might want to pay close attention to that.

    -Kelvin