AD7329 reference voltage

Hi all!

I'd like to use the AD7329 in my design.
  From what I understand, a 2.5V reference can be used to measure up to ±10V and a 3V reference can be used to measure ±12V at the analog input pins.
  Reading through the datasheet, it's not clear to me what reference voltage is needed when I want to be able to measure ±16.5V at the analog input pins.

Thanks in advance!

  • +1
    •  Analog Employees 
    •  Super User 
    on May 3, 2021 6:14 AM

    Hi, 

    The AD7329 has 4 options for input ranges and these are the 

    +/-10V, +/-5V , +/-2.5V and 0 to 10V. These ranges have a typical voltage reference of 2.5V. The highest input range of +/-10V is based on a maximum range of 4xVREF. If the VREF is changed to 3V, the maximum full-scale input range can be stretched to 12V. Note that the VREF is only specified for up to 3V only. Beyond this value may lead to errors in the ADC and it is not recommended to operate above the 3V VREF.

    Regards,

    Andrei

  • 0
    •  Analog Employees 
    on May 3, 2021 7:02 AM

    HI, 

    Just to add. May I know what is your application, and is the ±16.5V your max input range? If you can give us your specific requirements we can recommend an ADC that will suit your requirements. You may also want to consider using AD411x (AD4111, AD4112, AD4114,AD4115). The part have specified accuracy at  +/-10V but can be functional up to +/-20V with 2.5Vref and a single 5V supply. Please see the datasheet for your reference. 

    Thanks,

    Jellenie

  • Hi,

    Thanks for your reply! Slight smile

    I understand measuring higher voltages than 12V can result in measurement errors.

    This is okay for me, I will try to filter this in software!

    The absolute maximum ratings for an analog input is 16.5V (VDD+0.3V), and for the REF it's 7V (VCC+0.3V).

    Do I have to apply the maximum REF voltage to be able to measure 16.5V at the analog inputs?

    And if I want to measure voltages higher than 10V, do I still leave the range registers on the 10V setting?

    Regards,

    eutim

  • Hi,

    Thanks for your reply! Slight smile

    I'm measuring an array of 12V industrial analog sensors. The output of these is up to 12V, but the system is very noisy and therefore has peaks of up to 15-16V. As I need to be aware of these peaks as well, I don't want to filter these out before it goes into the ADC.

    I already bought a batch of the AD7329 IC's, so unless this IC is not usable for what I'm trying to do then I would rather not switch to a different IC.

    Thanks,

    eutim

  • 0
    •  Analog Employees 
    on May 3, 2021 8:46 AM in reply to eutim

    Hi, 

    Thanks for the details. With voltage of 3V, the range for +/-10V mode will be +/-12V. So the part can work with your max input range however any input voltage beyond this range will just result in a full scale code. 

    Thanks,

    Jellenie