6.2 Thermal Considerations

A potential for self-heating errors can exist if the MCP9808 SDA, SCL and Event lines are heavily loaded with pull-ups (high current). Typically, the self-heating error is negligible because of the relatively small current consumption of the MCP9808. A temperature accuracy error of approximately +0.5°C could result from self-heating if the communication pins sink/source the maximum current specified.

For example, if the event output is loaded to maximum IOL, Equation 6-1 can be used to determine the effect of self-heating.

Equation 6-1. Effect of Self-Heating
T∆=θJA(VDD×IDD+VOL_Alert×IOL_Alert+VOL_SDA×IOL_SDA)

Where: 

TΔ=TJ – TA
TJ=Junction Temperature
TA=Ambient Temperature
θJA=Package Thermal Resistance
VOL_Alert, SDA=Alert and SDA Output VOL (0.4 Vmax)
IOL_Alert, SDA=Alert and SDA Output IOL (3 mAmax)

At room temperature (TA = +25°C) with maximum IDD = 500 µA and VDD = 3.6V, the self-heating due to power dissipation TΔ is +0.2°C for the DFN-8 package and +0.5°C for the TSSOP-8 package.

Figure 6-1. DFN Package Layout (Top View).