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DAC8560: Not to drive the V_REF pin internally and externally

Mark Philip Felipe
Genius 11050 points
Part Number: DAC8560
Other Parts Discussed in Thread: DAC8550,

Hi Team, seeking some input

The data sheet says not to drive the V_REF pin internally and externally at the same time indefinitely.

 

We would like to use an external 3.3V reference instead of the internal 2.5V reference.

I looked around the website, but could not find anything on how much time is available to switch the reference voltage.

Our SPI signals will not be ready to disable the internal reference for ~30ms.

How long can we place an external reference on this pin while the internal reference is enabled?

 

Also,

We are using a supply VDD of 3.3V, and a VREF of 3.3V from a bandgap.

In our current design, the VREF pin will come up to 3.3V before VDD is at 3.3V.

Is this acceptable, or should we consider changing the design?

What happens to the output voltage while VDD increases to 3.3V and VREF is already set to 3.3V?

_______

Thank you.

-Mark

  • 0
    TI__Mastermind 42273 points

    Hi Mark, 

    Sanjay will review this and respond tomorrow. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    TI__Expert 5250 points

    Hi Mark,

     

    Driving the V_REF pin internally and externally at the same time for short duration (30ms in your case, there is no fix number as such) multiple times, might lead to pereormcane/reliability issues. Even though "data sheet says not to drive the V_REF pin internally and externally at the same time indefinitely". 

    So, we will not recommend this to have it in a working design. 

    And regarding the VREF coming up before VDD, it's not recommended also. Although it's not there in data-sheet, i will check with team and get back.

     

    Thanks,

    Sanjay,

  • 0 in reply to Sanjay
    TI__Expert 5250 points

    Hi Mark,

     

    Shorting the VERF external/internal for ~30ms might cause a very. high short-circuit-current momentarily (as internal VREF does not have short-circuit limit protection)  and it might cause very high temperature(beyond ABS MAX). It is low risk. option.

     

    You can replace the DAC8560 with DAC855, in case you are not intending to use the device internal VREF. DAC8550 is p2p without internal reference.

     

    Thanks,

    Sanjay,