AD7787 AIN2 input voltage range

If REFIN is tied to VDD on the AD7787, is the AIN2 input voltage range from GND to VDD (when configured as a unipolar input)?  Are there any issues with that configuration?  VDD=5V in my application.

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  • +1
    •  Analog Employees 
    •  Super User 
    on Feb 17, 2021 7:08 AM

    Hi Jessica,

    The AIN2 input voltage range varies depending on the mode of buffer you select. 

    When the mode is selected to unbuffered, the AIN2 input voltage will range from 0 to 5v based on the VDD of your application. But there is some disadvantage of using the unbuffered mode. First is you will have a limitation of RC values at the inputs. The second is will contribute to some gain errors in the system. 

    When the mode is selected to buffered, the AIN2 input voltage will only have a range of 0.1v to 4.9v. Since there is a 100mV headroom voltage at the buffers. But the advantage of using buffered mode is that it allows you to place source impedances on the front end without contributing gain errors to the system. 

     

    Regards, 

    Andrei

Reply
  • +1
    •  Analog Employees 
    •  Super User 
    on Feb 17, 2021 7:08 AM

    Hi Jessica,

    The AIN2 input voltage range varies depending on the mode of buffer you select. 

    When the mode is selected to unbuffered, the AIN2 input voltage will range from 0 to 5v based on the VDD of your application. But there is some disadvantage of using the unbuffered mode. First is you will have a limitation of RC values at the inputs. The second is will contribute to some gain errors in the system. 

    When the mode is selected to buffered, the AIN2 input voltage will only have a range of 0.1v to 4.9v. Since there is a 100mV headroom voltage at the buffers. But the advantage of using buffered mode is that it allows you to place source impedances on the front end without contributing gain errors to the system. 

     

    Regards, 

    Andrei

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