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ADS131A04: Internal reference setting

Dan Li62
Intellectual 420 points

Part Number: ADS131A04

Hi there,

I am using the chip ADS131A04 for sampling. I came across a problem related to the internal reference. On Page 31 of the datasheet, it states that 

By default, the external reference is selected (INT_REFEN = 0). The internal voltage reference requires 0.2 ms to settle to 1% and 250 ms to fully settle to 0.01% when switching from an external reference source to the internal reference (using the recommended bypass capacitor values).

Here, what does it mean by the internal voltage reference settle to 1% and 0.01%?

Thanks,

Dan

  • 0
    TI__Guru** 100695 points
    Dan,


    When the reference is enabled, it takes a certain amount of time before it gets to the reference value (for both 2.442V and 4V). There may be some sort of rise time like an R-C time constant as the reference is turned on and it may be dependent on the load capacitance of the reference.

    For example, in the datasheet the start-up time is given for a 1uF load capacitance. If the reference is 4V, then it would take 0.2ms to get to 1% of the final value. That would be 40mV, or to reach 3.96V. It would take 1.2ms to get to 3.996V and it would take 250ms to get to 3.9996V.

    This time is important because any error in the reference looks like a gain error in the measurement and you want to have a settled reference before you do any calibration or make measurements.


    Joseph Wu