AD5697R VREF

Dear Analog Support,

1) I want to connect an external 1.8V reverence to the VREF of the AD5697R. In 

the first page of the data sheet  the Table 1 indicates that the external
Vref is not supported, however Table 6 says the opposite. Can you clarify ?

2) What is the accuracy of the DAC if I connect a lower external VREF (1.8V) ?
I need an external VREF due to the external 1.4V full scale range device and at

the same time the need to get 12 bit accuracy with 1.6mV max output offset DAC error.

3) In the meanwhile I disable the internal VREF (via an IIC command), is
there any shortcut to VREF pin if I connect an external 1.8V VREF ?

Thanks
Paolo


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  • 0
    •  Analog Employees 
    on Mar 31, 2016 3:38 PM over 5 years ago

    Hi Paolo,

    The AD569R does support both internal and external references.  The table on page 1 is showing the default/typical type of reference used with the part.

    In terms of accuracy, the specifications are as per the data sheet spec table.  The offset error is spec'd as 1.5mV  (max), and is indpendent of the reference used.  The TUE (total unadjusted error) spec is a good one to get an overall 'accuracy' figure for the DAC, and is gain dependent, but can be 0.1% for Gain =1

    If you connect the external reference to the VREF pin from power-up, before disabling the reference over the i2c bus, then there will be contention between the two references, and could load the DAC reference (as it will be higher at 2.5V).  We would not recommend doing this, so if you can disconnect/power down the external reference until you disable the DAC reference that would be the recommendation.

    Regards,

    Michael.

Reply
  • 0
    •  Analog Employees 
    on Mar 31, 2016 3:38 PM over 5 years ago

    Hi Paolo,

    The AD569R does support both internal and external references.  The table on page 1 is showing the default/typical type of reference used with the part.

    In terms of accuracy, the specifications are as per the data sheet spec table.  The offset error is spec'd as 1.5mV  (max), and is indpendent of the reference used.  The TUE (total unadjusted error) spec is a good one to get an overall 'accuracy' figure for the DAC, and is gain dependent, but can be 0.1% for Gain =1

    If you connect the external reference to the VREF pin from power-up, before disabling the reference over the i2c bus, then there will be contention between the two references, and could load the DAC reference (as it will be higher at 2.5V).  We would not recommend doing this, so if you can disconnect/power down the external reference until you disable the DAC reference that would be the recommendation.

    Regards,

    Michael.

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