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DAC63202: Regarding to the VREF

Masakazu Adachi
Intellectual 2500 points
Part Number: DAC63202

Hello team,

I received a question from the customer. 

In 8.2 Typical Application, a 10kΩ resistor is inserted between VDD and VREF, is there any problem without this resistor? The customer seems to have configured the circuit referring to the Typical Application, but he says that even if 5V is applied to VDD, the voltage at VREF is 4.6V. Is there any possible cause for this?

Regards,

Masa

  • 0
    TI__Mastermind 29898 points

    Hi Masa-san, 

    Is the DIS-MODE-IN bit set to 1? 

    The pullup resistor to VDD is recommended for when the internal reference is not used so the pin is not floating. 

    The reference pin has a 192k input impedance, so the 4.6V might be coming from a voltage divider between that input impedance and the 10k resistor. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    TI__Intellectual 2500 points

    Hello Katlynne,

    Thanks for the support. 

    Katlynne Jones said:
    Is the DIS-MODE-IN bit set to 1? 

    The customer set to 0. Does this setting need to be set to 1 when using an external reference?

    Katlynne Jones said:
    The reference pin has a 192k input impedance, so the 4.6V might be coming from a voltage divider between that input impedance and the 10k resistor.

    If there is a 192k impedance, does it matter if I don't put a 10k pull-up resistor on it? Please let me know if there is any reason why I should put it on.

    Regards,

    Masa

  • +1 in reply to Masakazu Adachi
    TI__Mastermind 29898 points

    Hi Masa-san,

    The DIS-MODE-IN bit should be set to 1 to minimize leakage, but I don't think this is the source of the problem. 

    If they are using the 10k pullup then I think that is likely the issue. It would cause a voltage divider with the input impedance of the pin which is what I think they are seeing with the 4.6V on the pin. 

    You should not use the pullup when using the external reference. The recommendation was made when using the internal reference so the pin is not left floating. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    TI__Intellectual 2500 points

    Hello Katlynee,

    Thank you for your support. I will tell the customer to connect 5V directly when using an external reference.

    Regards,

    Masa