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TeInternal Temperature sensor o/p issue

Question asked by AMEY KHATAVKAR on Apr 14, 2016
Latest reply on Apr 18, 2016 by Radek Sestak

Hi Team,

I want to measure the core temperature for the MC9s12ZCM,

I have enabled Temperature sensor and configured voltage level generated by the temperature sensor is driven to a special channel input of the ADC Converter.

/* Temperature sensor/Bandgap voltage enable bit is enabled    */

    CPMUHTCTL_HTE = 1;

   

/*! Voltage Access Select Bit is toggled to read :
*   1) VSEL = 0, internal temp proportional to VHT
*   2) VSEL = 1, Bandgap refernce voltage (VBG)
*/

    CPMUHTCTL_VSEL = 0;

 

Also configured adc1 channel to read the result of temperature sensor with configuration

Temp Sensor, Internal_0, 4 clock cycles sample time

written {0x00,0xC8,0x00,0x00}, at address 0x00002040

With this configuration, I am getting the raw count for temperature sensor as around 1095:

 

Considering the ADC reference voltage as 5V (VADD =5V)

Voltage with count 1095 = 1.33 V (with 12 bit adc)

So, for calculating the physical value of temperature I am referring following formula :

VHT(temp) = VHT(150) - (150 - temp) * dVHT

 

where, as per electrical specification

VHT(150) = 2.33 V

dVHT = 5.05 mv/degree Cel(typical)

 

So for temperature range 150 to -40 degree VHT ranges from 2.33 to 1.37 V

But in my case for the adc count are read as 1095, so VHT measured is 1.33V which is not in acceptable range f 1.37V to 2.33 so temperature value is bellow -40 degree.

And I think this is not the valid scenario, Core temperature must not be too low.Please help me to resolve this issue. Let me know if I am missing any configuration

 

Regards,

Amey

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