topic Re: kea64 on board temperature sensor in Kinetis Microcontrollers

kea64 on board temperature sensor

kiran5 — Mon, 27 Feb 2023 07:27:56 GMT

Hi,

I am trying to calculate the temperature value using the onboard temperature sensor. I am not able to find the exact calculation formula. Please provide the details needed for the calculation of the on board temperature value

Thanks and regards

Kiran

Re: kea64 on board temperature sensor

Miguel04 — Mon, 27 Feb 2023 21:43:41 GMT

Hi @kiran5

This is the formula of the temperature sensor:

You can find more information in the AN3031 and the constant values are on the datasheet on table 12.

Best Regards, Miguel.

Re: kea64 on board temperature sensor

kiran5 — Tue, 28 Feb 2023 09:04:31 GMT

Hi @Miguel04

I used AN3031 document for calculating the Vdd. I am using 12 bit resolution and the typical Vbg value is 1.16 for KEA64. I got the ADCR value of the bangap channel around 300. So by using the formula

Vdd = 4095 * 1.16 / 300 which equals to 15.8 . Maximum Value of Vdd is 6v but here im getting it as 15.8v.

Am I missing something here??

Regards,

Kiran.

Re: kea64 on board temperature sensor

Miguel04 — Tue, 28 Feb 2023 18:20:30 GMT

Hi @kiran5

Can you tell me the number of resolution bits of the ADCR_BG value?

Best Regards, Miguel.

Re: kea64 on board temperature sensor

kiran5 — Thu, 27 Apr 2023 07:06:30 GMT

Hi Miguel04
The adc count from the ADCR register by enabling the temperature sensor is 1110. From this value I have calculated the Vtemp as 1110*5/4095 = 1.3431..
Here im using 5v reference voltage and 12 bit resolution.
The temperature is calculated from the formula
Temp = 25 - ((Vtemp-Vtemp@25)/Slope).
= 25 - ((1.3431-1.396)/0.003638)
=39.54
Here the temperature value i get is 39.54 Celcius.
We connected an external NTC resistor and calculated the temperature from that and the value observed was 34.
There is a difference of 5 celcius. Am i doing it the right way or should is do some changes.
Best Regards, Kiran