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ADC08D1020: Power On Calibraion

chao zh
Intellectual 650 points
Part Number: ADC08D1020

Hi,all.

I now don't want the calibration process to perform at power up of ADC08D1020. So how long  should the CAL pin be stable before the power up of ADC08D1020 to  prohibite the power on calibraion?

  • 0
    TI__Mastermind 43950 points
    Hi
    I am looking into this and will respond later today.
    Best regards,
    Jim B
  • 0 in reply to Jim Brinkhurst1
    TI__Mastermind 43950 points

    Hi

    To prevent Power On Calibration, the CAL pin must be held high until after the Calibration delay time has elapsed. Depending on the state of the CalDly pin this will be either 2^26 or 2^32 input clock cycles. If the input clock is not stable then the Calibration delay time is not well defined.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Intellectual 650 points

    Hi, Jim

    Thanks for your reply.

    I now use the same power as the ADC power supply to pull up the  CAL pin with a 1kΩ resistor,but Power On Calibration still work. Whether I must use another power that be stable before the ADC 1V9 supply begin to power up?

    Thank you again!

  • 0 in reply to chao zh
    TI__Mastermind 43950 points

    Hi

    I will look into this further and try to validate on a bench setup.

    Can I ask why you want to power-up the ADC in the uncalibrated state? The performance will be significantly degraded until it has been properly calibrated.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Intellectual 650 points

    Hi,Jim

    In my application,every time after the calibration of ADC,the signal process result will be some different with the result before calibration.I have validated this problem using On -Command Calibration.  So I want to prohibit the Power-On Calibration  to do further verification.

    Best regards.

  • 0 in reply to chao zh
    TI__Mastermind 43950 points

    Hi

    I've tried a number of different configuration settings and have not succeeded in inhibiting the initial power-up calibration that occurs. It may be that the note in the datasheet regarding that capability is incorrect for this device. Since the device must be calibrated to achieve rated performance this is not a fundamental requirement of the device.

    It is possible to calibrate the ADC the first time after power-up, and then prevent further calibration of the device by setting CAL always high. It is also possible to disable the input Resistor Trim calibration from occurring during subsequent linearity calibrations. Since changes from calibration to calibration of the input resistor trim can have effects on the input signal gain this can also be beneficial.

    If you really need a device where the calibration must be kept as similar as possible every time the part is powered up I recommend considering the ADC10D1X00 or  ADC12Dxx00(RF) devices.

    In these devices the part can be calibrated once, and the resulting calibration coefficients can be read out and stored. Then every time the ADC is powered up in the future, the previous calibration coefficients can be written back into the device, restoring the previous calibration settings exactly. Please refer to the section "Read/Write Calibration Settings" in those product datasheets.

    I hope this is helpful.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Intellectual 650 points
    Hi,Jim

    Thank you very much for your help in recent days.

    Best regards.