AD7791 Buffered

Are there errors, drifts or other forms of degradation to be expected if using the AD7791 in buffered mode? Is there a reason to have opamps like ADA4528 as input buffers and use the AD7791 in unbuffered mode? I need it for an RTD bridge-measurement with 1k resistors.

Kind Regards,

Akos Buzogany

  • +1
    •  Analog Employees 
    on Jan 24, 2021 3:41 AM 1 month ago

    Hi, 

    The analog input as well as the reference input is continuously sampled by a switched capacitor. In application such as RTD, the analog input and reference input is usually driven by an external reference resistor for a ratio metric configuration. Note that large RC values can cause gain errors in measurements. Enabling the internal input buffers allow a wide range of resistor values or EMC filtering without adding any error. Same with the reference, if your reference input will be driven by a large resistor value then it is also suggested to add external input buffers as this part do not have any internal reference buffers. But you may also want to consider are newer parts such as AD7124 it has both internal analog and input buffers with more advanced feature. 

    Please take note also that enabling the internal buffers will require some headroom, I think around 100mV for this part. 

    Thanks,

    Jellenie

  • Hi Jellenie,

    Does the built-in buffer in AD7791 have a drift or induces a bigger error compared to using an external ADA4528?