TMP1827: How much power do we expect consumed when powered by 1-wire

Cameron, 

Device current consumption will not increase under bus power. 4.2uA is not the max current consumption, because it will consume 94uA typ during a temperature conversion that lasts 3 or 5.5ms. 

thanks,

ren

In bus powered mode, device power comes from the pull-up resistor. Do you intend to power the resistor with a GPIO? This is not necessary for implementation.

Regardless, the max current through the resistor will occur when the bus is pulled down for a logic low. The resistor must be sized to not violate the 4mA VOL spec. Therefore, the max current is 4mA.

ren

Please see section 8.3.3 of the datasheet which describes different pull-up formulas based on the voltage used.

However, I don't recommend using the maximum resistor value. In Low-Power Design Techniques for Temperature-Sensing Applications, I conclude that the lowest power is achieved by running the highest speed that your bus capacitance will support. This is because lower speeds draw the high current for longer, and this outweighs the benefit of reducing the current. While this analysis was done on I2C, it applies to 1-Wire as well, since they are both open-drain with similar frequencies and currents. 

thanks,

ren

Standby current is only used in Continuous conversion mode. The lowest power will be achieved in Shutdown mode, with One-Shot commands sent to trigger measurements (conversions) as needed. This is described in 8.4.1 Device Functional Modes.

thanks,

ren