The TIDA-00848 PCB can accommodate the TMP63 sensors thru an extension flex PCB or similar, as one temperature sensor measures the radiator body (or heater sensor), and the second sensor captures the room temperature (or room sensor). Any HCA device is mounted firmly onto the heater body, and the heater temperature sensor must have thermal (but not electrical) contact with the heater body. In contrast, the room temperature sensor is orientated into the opposite direction to the room or away from the heater body. The two sensors approach used in this TI Design is described in the EN 834 as the two-sensor measurement method.

For easier evaluation the circuitry with the two TMP63 sensors and the TLV2333 devices can be attached over the two extension headers J9 and J11. Although no hardware design has been done yet, a TINA TI Spice simulation file for each sensor circuit is provided. Both sensor utilize a Current biasing scheme, using the programmable current source module inside the SCE. Two files, one per TMP63 sensor, are included in the Simulation file example at TIDA-00848 folder.

The simulation shows the plot from 18 to 95 °C and 10uA current source excitation thru the CC1312R programmable current source into TMP6331 device. At x = 500m the 18°C minimum is at 2mV voltage level to the ADC12, while at x = 1500m and 95°C the output voltage is 2.1V, when using 2.1V as supply voltage to CC1312R.

The 2.1V supply were chosen, as the end-of-life voltage at the end of lifetime of a 3V LiMnO2 primary cell, which are commonly used in Heat Cost Allocators. The ADC12 module can use VDDS as the reference voltage and thus utilize tthe range of 0V to 2.1V as the full ADC scale, even when VDDS drops over lifetime from 3.25V (new cell) down to 2.1V (representing an empty battery cell).

The signals on TIDA-00848 PCB available for temperature sensing are:

• DIO_28 = Vtmps_1
• DIO_27 = Isrc_1 (analog output to the first TMP63 sensor) - in this design re-purposed as BASE_PWM_N signal to drive the LCD
• DIO_29 = Iscr_2 (analog output to the second TMP63 sensor)

The temperature sensing code has not been implemented and tested yet. The code can be written for the main M4F MCU core, as typically temperature is measured 1-2 times per minute and power penalty is low, especially if combined with other periodic application code functions. Alternatively, the SCE module can be used for converting the ADC12 codes into temperature values, as existing SCE RAM usage with both touch and LCD tasks is 35.7% or 731 words (16-bit long) and leaves plenty of RAM free for temperature code calculations. If the SCE is used for this code, then careful alignment of task timings is mandatory, as LCD frame timing must have the highest priority; where the other tasks must be scheduled in between the LCD frame activity.