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DAC60501: REF-ALARM bit set and no output, but VCC = 3.25 V and VREF = 2.5 V

Matt Bruensteiner67
Prodigy 220 points
Part Number: DAC60501

I am seeing no output (0 V regardless of code setting) from DAC60501.

Vcc is 3.25 V (measured) and VREF output is 2.5 V (measured). 

The REF-ALARM bit in the STATUS register is reading as 1. The datasheet says this bit "reads 1 when the difference between the reference and supply pins is below a minimum analog threshold.Reads 0 otherwise."

I don't find that the minimum analog threshold is specified in the datasheet. What is the minimum Vcc to avoid this condition? Are there any other conditions that can cause the REF-ALARM bit to be set? What settings can be used to get a non-zero output from the DAC?

Other observations:

* Register 01h reads as 2195h. This doesn't match the datasheet spec which says field [11:8] should be 4 rather than 1.

* I see the REF-ALARM bit set for all settings of the REF-DIV and BUF-GAIN bits.

Thanks,

Matt

 

  • 0
    Prodigy 220 points

    I tested a 2nd time, and if I set the GAIN register to 0x0100 (REF-DIV set and BUF-GAIN clear) then the ALARM bit might clear and I will get output from the DAC.

    But I would like to have 0 - 2.5 V range, not 0 - 1.25 V.

  • 0 in reply to Matt Bruensteiner67
    TI__Mastermind 18546 points

    Hi,

    Thanks for writing to us.

    Since your supply voltage is 3.25V, we internally have a reference buffer which has got headroom requirements approx 1.5V, with that you cannot have 2.5V buffered reference . So you need to divide the reference which is what REF_DIV will do. So it will become 1.25V and are good to go.

    And for 0 to 2.5V output, you just set gain of the ouput buffer to 2 by setting BUF_GAIN.

    This headroom requirements if its violated, ALARM bit will be set, this is what you are observing.

    For your application, REF_DIV  = 1, BUF_GAIN  =1 will give you 0 to 2.5V output voltage.

    please see below datasheet information on the reference config for different supply voltages.

    Regards,

    AK