During ADC conversion, some power is dissipated that heats the device despite the small power consumption of the TMP119. Consider the self-heating effect (SHE) for certain precise measurements. Figure 8-3 shows the device SHE in still air at 25°C after the supply is switched on. The device package is soldered to the 11mm × 20mm × 0.7mm size coupon board. The board is placed horizontally, with the device on top. The TMP119 is in continuous conversion mode with 64 sampling averaging and zero conversion cycle time. There is no digital bus activity aside from reading temperature data one time each second. As shown in Figure 8-3, the SHE stabilization time in still air is greater when the device dissipates more power.

The SHE drift is strongly proportional to the device dissipated power. The SHE drift is also proportional to the device temperature because the consumption current with the same supply voltage increases with temperature. Figure 8-4 shows the SHE drifts versus temperature and dissipated power at 25 °C for the same coupon board and the same conditions described previously.

To estimate the SHE for similar size boards, calculate the device consumption power for 25°C and use the corresponding power line shown in Figure 8-4.

The following methods can reduce the SHE:

• System calibration removes not only the self-heating error and power-supply rejection ratio (PSRR) effect but also compensates the temperature shift caused by the thermal resistance between the device and the measured object.
• If practical, use the device one-shot mode. If continuous conversion is needed, use the conversion cycle mode with significant standby time. For example, in most cases an 8-sample averaging (125ms) with a 1-second conversion cycle provides enough time for the device to cool down to the environment temperature and removes the SHE.
• Use the minimal acceptable power supply voltage.
• Use a printed-circuit board (PCB) layout that provides minimal thermal resistance to the device.
• Avoid using small-value pullup resistors on the SDA and ALERT pins. Instead, use pullup resistors larger than 2kΩ.
• Ensure that the SCL and SDA signal levels remain below 10% or above 90% of the device supply voltage.
• Avoid heavy bypass traffic on the data line. Communication to other devices on the same data line increases the supply current even if the device is in SD mode.
• Use the highest available communication speed.