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F28027 internal temperature sensor problem

ari pikivirta
Prodigy 40 points

Have anybody noticed offset being changed runtime on F28027?

VREFLO is tied to ground very close to pin, amd everything looks as they should on circuit. For some reason when I enable AND chip (74HCT08) where anded pins are at 5V and those that are being controlled (other AND part) are connected to GPIO0-3 internal temperature is showing huge offset to the measurement. Have anybody else experienced this kind of temperature offset value change for simiilar or any other reason?

  • 0
    Guru 13185 points

    Hello,

    Actually I don't understand what the offset that you meant is.

    But I am wondering, as far as I know, there is only one internal temperature sensor in F28027F and it is in ADC pin A5.

    So what are they in GPIO0-3?

    Best regards,

    Maria

  • 0 in reply to Maria Todorova
    Prodigy 40 points

    Offset comes to the internal temperature reading (ADCIN A5).

    GPIO0-3 is set as output for PWM channels and should not have directly anything to do with the reading., but those are connected to the AND circuit of which other port is connected to +5VDC signal. When this other and input is connected, it seems to affect also the temperature reading by adding the offset to it's value. I cannot understand what is really causing this offset to be added by just doing this.Because I don't understand why connecting these outputs to and input could cause this to happen, I'm asking if anybody has seen temperature sensor offset to occur for some other (or similar reason).

  • 0 in reply to ari pikivirta
    TI__Guru 60865 points

    Hi Ari,

    Can you draw your circuit, with the voltage levels of of each line for the GPIOs and AND gate?

    Also, can you quantify how much the temperature sensor offset changes?  What is the reading, in LSB, before and after you enable the AND gate?

  • 0 in reply to Devin Cottier
    Prodigy 40 points

    Sure, but seems like it's not necessary anymore.

    Problem was not with anything with the pins conencted, but internal temperature sampling window. Results seemed to have the offset generated by some minor difference in times between those and got corrupted ON BOTH cases. Now temp seem valid with just soc sample window increased to 24 from 7.