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ADS7142: BUSY/RDY_BAR signal not going high after writing OFFSET_CAL reg (0x15 to 0x01)

Kyle Craig
Prodigy 30 points
Part Number: ADS7142


I am using the ADS7142 and about the only operation that I cannot get to successfully execute is a calibration step using the OFFSET_CAL register. 

After writing that register the BUSY/RDY_BAR signal never goes high as suggested in the datasheet. For any other operation (starting ADC readings via START_SEQUENCE register, software reset via general call) the BUSY_RDY signal instantly goes high when the command is written. I have probed the following three signals SDA, SCL, BUSY/RDY_BAR using a saleae and compared them to the images in "TM4C1294 interface to ADS7142 software library (Rev. A)" and the I2C commands for calibration look exactly the same. 

Are there any other steps need to get periodic offset calibration to work?

  • 0
    TI__Mastermind 25030 points

    Hello,

    The BUSY pin after an offset calibration has proven to occur so fast that sometimes it changes state and back within a clock pulse. 

    Thus it is possible that you may not be observing it. 

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 30 points

    Hello!

    I have my Saleae set to 500MS/s when observing these signals.

    Also, in our setup I can see noticeable improve in the ADC value (nearly 100  LSBs) when I perform general call reset of the device vs running it with only the built in calibrate register write. I've also observed this same behavior across multiple parts.

    Thanks!

  • 0 in reply to Kyle Craig
    TI__Mastermind 25030 points

    Kyle,

    How are you setting up the calibration?

    Would you try following the below diagram. Using

    OpCode =  00001000b

    Reg Address = 0x15

    content = 0x01

    When you say that you see an improvement after reset, how are you comparing it to when a calibration is manually done?

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 30 points

    Cynthia, 

    We are currently running that I2C command. The output I have from my saleae logic analyzer matches the screen grabs shown in TM4C1294 interface to ADS7142 software library (Rev. A) document for using this part with an eval kit. 

    We are succesful in setting the part into high precision, I can change the oscillator settings and nCLK settings. I can send I2C commands to start sample. The only command I seemingly cannot get to function is the calibrate. 

    Kyle

  • 0 in reply to Kyle Craig
    TI__Mastermind 25030 points

    Hello Kyle,

    Can we try something to see if the calibration is in fact taking/not taking place

    Would you please:

    1)      Reset the ADC.

    2)      Apply 10mV input to the ADC, Record ADC uncalibrated output code. There will be an offset error.

    3)      Now run offset cal.

    4)      Apply 10mV input to the ADC, Record ADC calibrated output code. There will be a lower offset error.

    This will help to determine if the calibration is being done, and if it is not being captured by the ready signal

    Regards

    Cynthia