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[FAQ] How do I calculate the average power consumption of my digital temperature sensor?

Guru 62280 points

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How do I calculate the average power consumption of my digital temperature sensor?

BR-

Josh

  • Using the TMP112 as an example, from that datasheet, sections 7.4.1 and 7.4.3 contain the information to calculate the average power consumption

    Continuous sampling:

    • Conversion: 26mSec @ 40uA I2C read: 20uSec @ 40uA (current draw through the I2C pull-ups not included). Note that this time varies based on the system I2C speed.
    • Quiescent current: 2.4uA

    For example,

      • if you sample at the slowest setting (0.25Hz), then the average current would be (0.25*26mSec*40uA) + (0.25*20uSec*40uA) + ((1 - 0.25*26mSec - 0.25*20uSec)*2.2uA) = 2.4 uA avg (excl. I2C pull-up resistor current)
      • if you sample at the fastest setting (8Hz), then the average current would be (8*26mSec*40uA) + (8*20uSec*40uA) + ((1 - 8*26mSec - 8*20uSec)*2.2uA) = 10.1 uA avg (excl. I2C pull-up resistor current)

    One shot mode

    • In one shot mode, the calculation is similar to the one above, except:
      • two I2C transactions per conversion are required (trigger and read)
      • use shutdown current instead of quiescent current during idle times (500nA typ)

    For example,

    • if you sample at the at one Hz using one shot mode, then the average current would be (1*26mSec*40uA) + (2*20uSec*40uA) + ((1 - 1*26mSec - 2*20uSec)*500nA) = 1.5 uA avg (excl. I2C pull-up resistor current)

    BR-

    Josh

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