Temperature compensation on MC9S08QB4

[benthie]

Hi erveryone,

I´m about to implement a temperature compensation on a MC9S08QB4. I already read the application note AN3031 in order to get some information about how to get a higher accuracy and the calibration procedures. So far so good.

I think I also understood, that for my application the knowledge of an exact temperature is not important. The ADC value of the sensor is enough to compensate the error due to temperature changes !?

What I definitely do not understand is whether I have to bring the sensor value in relation to the current bandgap value or not. In other words: do I have to determine current V_DD by using the bandgap voltage in order to get a accurate sensor reading V_TEMP or is it nonsense in this case?

Regards,

Ben

[pavel_sadek · Accepted solution]

Hi Ben

For different supply voltages you will get different ADC readouts - see the figure 1 of the AN3031, you need to know the supply voltage as Vtemp25 is stated for 3V supply in the datasheet.

So you need to know the correct supply voltage - the band gap voltage reference will help you to figure out (measure) what is the correct supply voltage (you will get ADC representation of 1.17V) and this way, you can recalculate ADC readout correctly to junction temperature of the chip.

there is also code for the AN attached in Freescale pages, so you can adapt it more easily to your MCU/ board.

Pavel