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TLV5638M: Disabling buffer for external reference

Alberto Miguez
Prodigy 70 points

Part Number: TLV5638M

Good morning,

I am using the TLV5638MDREP Digital to Analog converter and I would like to use an external reference. I am currently using the 1.024V reference with a VDD of 3.3V. I have tried connecting the REF pin to the VDD pin to have an external reference of 3.3V, but I am not achieving the expected values from the DAC. 

The datasheet, in page 3 Note 1, talks about having to disable the output buffer of the internal reference, if an external reference is used.

I am unsure as to how to disable the output buffer. I read the datasheet but couldn't find anything regarding this.

Please let me know if you can help.

Thanks,

Alberto Miguez

  • 0
    TI__Mastermind 42253 points

    Hi Alberto, 

    You should just need to write to the DAC control register (set R1 and R0 to 0b11) and set the reference bits to 0b11.

    Let me know if this works for your issue. If not, please elaborate on the unexpected output you are seeing. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 50 points

    Katlynne,

    Thanks but this is not our issue. We believe we are seeing the clipping described in Note 1 on Page 3 of the datasheet. It mentions that we need to disable the buffer to avoid this clipping when using an external reference but does not mention how to do so.

    Basically, our output voltage as a function of the number of counts we are sending is not linear when using the external reference (we are using 3.3V external reference). The output approaches 3.3V sooner than it should. Everything functions as expected when using the internal references.

  • 0 in reply to Ryan Thompson
    TI__Mastermind 42253 points

    Hi Ryan,

    There is not another way that I know of to disable the buffer. I have ordered a few parts to test myself. They should arrive next week and I can try to replicate your issue. 

    Can you share a few data points before and after the clipping? Something in the form of Output code = x, Output - x V. At what code does the clipping start?

    Best,

    Katlynne Jones