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ADS114S08: Can not read Temperature over SPI from ADS114S08

Karne
Prodigy 210 points

Part Number: ADS114S08

Hello,

For unknown reason when I try to read Temperature over SPI ADS114S08 just return 0's. While there is no problem to read any of the external analog inputs. All registers reads and writes ok.Means SPI communication is ok. Device is set in single conversion mode, conversion is started with START pin, then waiting for DRDY low, which occurs in expected time - just same as it does with external AINx connected. Means conversion happens. Also tried to measure power rails by changing SYS reg value - also no luck. I suspect something wrong with internal interconnect?

Can somebody confirm that Temperature is realy readble on real part? Or anything wrong in my circuit? Or something wrong with registers? Here is attached connections and also registers dumped from real life part right after the end of conversion.

 

  • 0
    TI__Guru 60412 points

    Hi Karne,

    I suspect this may be happening since you are writing 0x8 to the gain setting register 03h instead of 0x08 as I think you intended. 

    The PGA must be enabled in order to read from the internal temperature supply. 

    Give that a try and let me know if it helps. 

  • 0 in reply to Alexander Smith
    Prodigy 210 points

    0x8 and 0x08 is acutally a same number. Compiler does recognoze it normally. Any way jsut tried this - nothing changes. Here is screen from actula debugger with dumper register values shown in binary representation.

    Reg "03" = 1000  what is same as 000 01 000  and as per datasheet   this is  000=>14tMod,  01=>PGAenabled, 000=>Gain1

    The same Reg03 settings used with external inputs where it works ok.

  • 0 in reply to Karne
    TI__Guru** 113765 points

    Hi Karne,

    Try disabling the global chop in register 0x04.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 210 points

    yehh, solved

    Beeing not the deep expert of particular chip - who could guess this...  

    I think that is no mentioned in datasheet - or I missed that?

    Thanks a lot ayway

  • 0 in reply to Karne
    TI__Guru 60412 points

    Thanks Bob! 

    Karne,

    I believe that the feature was simply averaging two measurements, one positive and one negative, that resulted in a return of 0. This is the intended function of the feature - so it is not mentioned to explicitly not work with the internal temperature measurement. 

  • 0 in reply to Alexander Smith
    Prodigy 210 points

    Yes, now it it is obvious when somebody told.

    But beeing the end user - how to guess at which point choper swap switch is located? Is it before sensor inputs or after? When nothing said it is reasonable to assume that sensor wires and AINx are equivalent.

  • 0 in reply to Karne
    TI__Guru 60412 points

    I agree that it is somewhat ambiguous. Looking at the block diagram on the first page of the datasheet you can see that the temperature sensor feeds into the MUX. Then looking at figure 73. you can see the the global chop takes place between the MUX and the PGA.