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ADS1263: Problems with conversion result on some ADC channels

Simon Mali1
Prodigy 130 points
Part Number: ADS1263

I am using an ADS1263 for ADC conversion on channels 1 to 9. I can see that some channels works as expected but some other channels show positive overflow at input voltages in 0V range.

Here is my printout:

ADC device 1 channel 7: Raw Value=0x7fffffff (2147483647) Voltage=2.500100V Conversion Data Ready Bit=1; PGA Low Error=4, PGA High Error=4, PGA Diff. Error=4, No of Conversions=4

Conversion readout CRC is ok.

And here is my register map printout:

spi_adc_ads1263_regmap
Status printout of spi ADC ADS1263:
    1. ADC ADS1263 32 bit IC40 SPI address 3 index 0:
    1a. ID=0x23:
    1b. power=0x11:
    1c. interface=0x5:
    1d. mode0=0x40:
    1e. mode1=0x80:
    1f. mode2=0x82:
    1g. inpmux=0x7a:
    1h. ofcal0=0x0:
    1i. ofcal1=0x0:
    1j. ofcal2=0x0:
    1k. fscal0=0x0:
    1l. fscal1=0x0:
    1m. fscal2=0x40:
    1n. idacmux=0xbb:
    1o. idacmag=0x0:
    1p. refmux=0x0:
    1r. tdacp=0x0:
    1s. tdacn=0x0:
    1t. gpiocon=0x0:
    1u. gpiodir=0x0:
    1w. gpiodat=0x0:
    1v. adc2cfg=0x0:
    1y. adc2mux=0x1:
    1z. adc2ofc0=0x0:
    1q. adc2ofc1=0x0:
    1aa. adc2fsc0=0x0:
    1ab. adc2fsc1=0x40:

 Do you have some idea why this is happening?

Best regards Simon Mali

  • 0
    TI__Guru** 113765 points

    Hi Simon,

    Welcome to the E2E forum! I apologize for the delayed response. Can I see your schematic?  If you are seeing a positive full-scale (+FS) reading and the input is 2.500100V, then I would expect a +FS when using the internal reference which is 2.5V.  So I need a little more information as to what is connected to AINCOM and AIN7.  Also, help me understand what you mean by '0V range'.

    If you are connecting an external voltage that is 2.5V to AIN7 and 2.5V to AINCOM, then I would expect a conversion result closer to 0.  Is this how you are connecting the supplies? If you are using an external source, you must make sure that the grounds are connected.  I would also suggest checking any solder connections at the ADS1263 to make sure the connections are soldered correctly.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 130 points

    Hi Bob

    Thank you very much for your reply.

    Problem is solved. I had a short circuit on the board. Now the ADC is working according to my expectations. Sorry for bothering you.

    But maybe you can answer my question regarding reference. In case of using +-2.5V power supply for ADC how are you planned to use internal 2.5V reference? I guess more convenient would be to use 2.048V internal reference or something similar? Is there some trick or I have to use external reference in case of +-2.5V PS?

    Best regard

    Simon M.

  • 0 in reply to Simon Mali1
    TI__Guru** 113765 points

    Hi Simon,

    You could use an external reference, but there is no reason why you cannot use the internal reference.  What may be confusing is the reference is referred to AVSS and not AGND. When measured from REFOUT to AGND you would see around 0V, but if you measure from REFOUT to AVSS you will see 2.5V. which is the actual reference voltage out of the ADS1263.  When you select the internal reference voltage (2.5V) the full-scale range will be +/- 2.5V/(PGA GAIN).

    Best regards,

    Bob B