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Original question:

ADS1248: ADS1248 System Monitor Issuse

ADS1248: VREFOUT reading 0V

Suraj mhaske
Prodigy 90 points

Part Number: ADS1248

Hi,

I am using ADS1248 on my custom board and my circuit is similar to   I am able to use all the system Monitor function and get correct readings but when I am using external reference connected to REFP0 and REFN0 by writing 0x00 to MUX1  and checking the voltage across VREFOUT I am getting 0v. Is there any other setting that needs to be done? If I  use internal reference then I am getting correct voltage across VREFOUT and GND

  • 0
    TI__Guru** 113765 points
    Hi Suraj,

    The internal reference comes out the VREFOUT pin. I think you may be confusing the MUX selection where the internal reference is on and also connects to the REF0 inputs (MUX1 setting of 0x18). The internal switches only work if the internal reference is selected and not when the REF0 input is selected.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 90 points

    Hi,
    So to be clear if I select REFP0 and REFPN0 as my reference I will not get any voltage on VREFOUT. To use REFP0 and REFN0 I should disable internal reference. ie. write 0x00 to MUX1?

    Thank You

  • 0 in reply to Suraj mhaske
    TI__Guru** 113765 points
    Hi Suraj,

    I admit that this is a little confusing. You will only see a voltage on VREFOUT if the internal reference is turned on. I'm not clear as to why the device was designed to be able to switch the internal reference out the REF0 pins.

    If you want to make an RTD measurement with an IDAC source, you must have the internal reference turned on, but you do not need to use the internal reference for your conversion reference. You might be making a ratiometric measurement using the IDAC source not only as the excitation source, but also the source of an external reference that is also excited by the IDAC. This reference voltage can be connected to the REF0 inputs. As the internal reference might be a much different voltage than the conversion reference, you would not want the internal reference to be connected to the REF0 inputs. In this case you would not want to use the MUX1 setting of 0x18.

    Best regards,
    Bob B