TMP61: How to replace RTD in cold junction compensation

Hi Woney,

1. The TMP61 has an operating range of -40C to 150C so you can definitely use it to sense cold temperature. You can check out the Thermistor Design Tool, which offers the complete resistance vs temperature table (RT table) computation. 

2. To ensure fast thermal response, the TMP61 should be placed directly next to the junction as close as possible. Some other best practices are: bottom side mounting (directly underneath the heat source), use vias to transfer temp quickly between the top/bottom sides of the PCB, use a solid ground plane around the thermistor and heat source. Refer to this app note: How to monitor board temperature. 

Another option is to calculate the temperature by taking differential temperature measurements, which enables a highly accurate temperature monitoring using two TMP61 thermistors. Here is the app note with more details: Component Temperature Monitoring Using Differential Temperature Measurements. 

3. Yes, the TMP61 is a 2 pin device. 

4. Thanks to the TMP61's linear positive temp coefficient, you can use a single-point offset calibration to achieve +/-1C accuracy or better across temperature. This app note explains the steps needed to achieve high accuracy with TMP6x thermistors: How to Achieve ±1°C Accuracy or Better Across Temperature With Low-Cost TMP6x Linear Thermistors. 

Best regards,

Sakeenah Khan

Hi Woney,

The series resistance could have an impact, but it depends on the expected temperature measurement range. Please see the attached device resistance table for reference. A significant series resistance should just add an offset (not affecting the slope of the TMP61's temperature response) so to mitigate any issues, you could perform the single-point offset calibration at room temperature. 

Best regards,

Sakeenah Khan

Thermistor Design Tool - Voltage Bias.xlsm