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REF6041: About the output impedance

diverger
Expert 1195 points
Part Number: REF6041
Other Parts Discussed in Thread: ADS8881, REF70, REF54, TINA-TI

Hi,

I'm considering using REF6041 to replace my VREF + OP combination, 'cause the built-in buffer of the former. From the 'Load Regulation' specification I calculated that the output impedance in worst case is about 123 mOhm and the typical value only 8 mOhm. But the 'Output Impedance' specification states the typical value is 50 mOhm.

Why there is so big difference between the typical value calculated from 'load regulation' and the 'Output Impedance' specification? Which one should I use in my signal chain calculations?

Regards.

  • 0
    TI__Expert 5000 points

    Hello,

    For your signal chain calculations, I would use the typical 50 mOhm value. This is because output impedance is a small signal parameter that is supported for output current changes of a few hundred µA and is defined over a frequency range as stated in the datasheet and shown throughout other figures in the datasheet as well.

    Load regulation is a DC parameter that depends on factors outside of small signal conditions, such as whether or not REF6041 is sourcing or sinking current and it is considered for currents up to 4 mA for REF6041. Additionally, in the datasheet the load regulation and output impedance parameters are reported with different test conditions, including different capacitive loads.

    Thanks,

    Jackson

  • 0 in reply to Jackson Wightman
    Expert 1195 points

    Hi,

    I saw some docs talking about how to choose ADC references based on the ADC reference input current. The 'allowed' reference output impedance of the ADC is calculated from reference voltage and bits count. Such as for ADS8881 the allowed impedance is, assume 5V reference voltage, and half LSB bit error:

    5V / 2^19 / 300uA = 32 mOhm

    It seems for a 18 bit ADC, the 50 mOhm impedance is much bigger. Certainly, I'm not very confident with this method. So, what's the option of TI guys, as REF6x series are advertised can drive 18-bit ADC.

    BTW: Are there a PSpice model for REF6041?

    Thanks.

  • 0 in reply to diverger
    TI__Expert 5000 points

    Hello,

    REF6x would be able to work with ADS8881 to preserve the performance of the ADC as specified in the datasheet, and it is used on ADS8881EVM2-PDK.

    We have more precise and accurate voltage references such as REF54 and REF70, but those would require an external buffer, unlike REF6x.

    There is not a REF6041 PSpice model available, but a REF6041 TINA-TI model is available at https://www.ti.com/product/REF6041#design-tools-simulation 

    Thanks,

    Jackson