MAX31855 internal temperature

Hi all, I'm using a sketch on Atmega328 reading internal temperature from MAX31855 in a loop. I see that internal temperature raise from room temperature to 40 or more degrees. Is this normal?

Sounds wrong, that chip has an expected supply current of 0.9mA, so would dissipate a few mW.

Are you running it at 5V? - its a 3V part...

Yes I use a 3.3V regulator from 5V of a power bank. With the same 5V I supply atmega328

Does the chip feel warm? Then the sensor is working properly. I don't know where the heat might be coming from. Perhaps you can see if there's anything hot nearby.

pazzokli: Yes I use a 3.3V regulator from 5V of a power bank. With the same 5V I supply atmega328

Its a 3.3V chip, so the ATmega must also be run at 3.3V or a level-shifter used on the SPI bus. The heat is from the input-protection diodes on the chip carry high current - your ATmega will also have been getting hot. If you are lucky you won't have damaged either, but its quite possible, as this is well outside the "absolute maximum" ratings of the chip.

Hi Mark, I think you centered mi problem. I didn't think to the bus when I drew mi board

Thanks :)