SBASA22A september 2022 – july 2023 ADS131B26-Q1
PRODUCTION DATA
The shunt temperature in this example is measured using the TMP61-Q1, a linear 10-kΩ PTC, in a typical voltage divider configuration using the analog supply (AVDD) as excitation. The PTC resistance is calculated using Equation 25, which is derived from Equation 24:
The maximum input voltage on V1A is limited to 1.25 V when using gain = 1 for ADC2A with the negative multiplexer channel of ADC2A internally connected to AGNDA. Therefore, the value of the precision resistor, R6, must be chosen so that the voltage on V1A stays below 1.25 V for the value range of the PTC across the temperature range to be measured. The TMP61-Q1 has the largest resistance at the most positive temperature, approximately 18 kΩ at +125°C. Following Equation 25, that means R6 ≥ 29.5 kΩ. A value of 34 kΩ is chosen for R6 to allow variation in the AVDD supply voltage up to 3.6 V without exceeding the maximum V1A voltage of 1.25 V.