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ADS1274: DIGITAL VALUE GETTING IS INCORRECT WHEN MORE THAN 1 CHANNEL IS CONNECTED.

AJITH KUMAR
Intellectual 470 points
Part Number: ADS1274
Other Parts Discussed in Thread: TM4C1294NCPDT, , ADS1278

HI TI TEAM,

We are using TM4C1294NCPDT microcontroller is interconnected with Ads1274 ADC module. When we connected only one channel at a time we are getting correct digital value. But when we connected more than a one channel is connected mean adc digital value is getting is incorrect. For example channel 1 and 2 connected means getting incorrect digital value or channel 1,2,3, and 4 is connected means getting incorrect digital value..etc . 

kindly guide us what may be a problem was caused. I have attached the ADC Schematic below,

Thanks in Advance,

Regards,

A. Ajith Kumar

  • 0
    TI__Mastermind 40610 points

    Hello Ajith,

    I see that you are only using a single DOUT pin, so I assume you are using the device in TDM mode.  Are you using SPI or Frame Sync?

    Please confirm the state of the other control pins and the CLK frequency.

    CLKDIV, FORMAT[2:0], MODE[1:0], TEST[1:0].  Also, /SYNC and /PWDNx should be held high during normal operation.

    Also, assuming you are in SPI mode, you need to monitor the DRDY pin for a falling edge, and then clock data out of the device before the next conversion cycle.  If SCLK is not high enough frequency, then you will not be able to capture all data and the results will be corrupted.  For ADS1272, f-SCLK needs to be greater than 0.5*f-CLK frequency to support 4 channels over a single DOUT pin.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Intellectual 470 points

    Hi Keith Nicholas.

    Thanks for response,

    We have given 27MHz fclk,0.5*f-CLK=13.5MHz minimum required. Our sclk is 27MHz. So it is sufficient to support 4 channels over a single DOUT pin. 

    Now, we are getting 1-6 channel data is correct. The channel 7 & 8 data is not getting but the convertion cycle is completed. 

    Thanks and regards,

    A. Ajith Kumar

  • 0 in reply to AJITH KUMAR
    TI__Mastermind 40610 points

    Hello Kumar,

    Please provide a logic or scope capture of the digital interface for one frame.  I suspect you are not reading the data at the correct time.

    Also, I assume you are using SPI mode and the ADS1278 since you are trying to capture more than 4 channels; please provide the following signals:

    /DRDY, SCLK, DOUT

    Regards,
    Keith