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

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)