CC2540 Temperature sensor Calibration

Hi,

I used the statements below to call out the calibrated data for adc and temperature.

        uint16 adcCalInt0V2 = *((uint8 *)INFOPAGE_WORD12 + 0) << 6 | *((uint8 *)INFOPAGE_WORD12 + 1) >> 2;        

        uint16 adcCalInt0V9 = *((uint8 *)INFOPAGE_WORD12 + 2) << 6 | *((uint8 *)INFOPAGE_WORD12 + 3) >> 2;        

        uint16 adcTemp25= *((uint8 *)INFOPAGE_WORD7 + 2) << 6 | *((uint8 *)INFOPAGE_WORD7 + 3) >> 2;

I got the values below.

         adcCalInt0V2 = 1311  

        adcCalInt0V9 = 5916  

        adcTemp25 = 5793

Internal Reference: MAX_CODE / ((v09 – v02)/0.7)  using 14-bit resoution

        Calculated Internal Reference = 1.2453 V

From datasheet cc2540,

        Internal Reference = 1.24V  Temperature coefficient: 4.5 /1°C at 12-bit resolution.

        By calculation,  Temperature coefficient = 2.7259 mV/1°C

I used my thermometer to verify the data. At 14-bit resolution,

        at my thermometer reading 24.0 °C, adcMyTemp240 = 5566  

        at my thermometer reading 22.9 °C, adcMyTemp229 = 5548

        Calculated Temperature coefficient = 2.4874 mV/1°C  that matches datasheet values.

Based on the Temperature coefficient from datasheet,

        if adcMyTemp250 = 5793

        By calculation, my temperature = 36.6 °C not equal to 25 °C

        Based on the adc output values adcMyTemp240 and adcMyTemp229 , adc output at 25 °C is expected to be around 55XX.

Why does the calibrated temperature value at 25°C off a lot from the actual value ?

I tried 1-point or 2-point calibrations to complete my temperature conversion; but the results are incorrect in both cases.

How can we eliminate temperature calibration in production? Can Ti provide an additional data point for 2-point temperature calibration?

Best Regards,

CK Lui