3V/5V Precision DACs - Which internal reference should I use?

Some of our nanoDACs have an on-chip reference. There are 1.25V and 2.5V reference options available. If we look at the table at the bottom of the figure below we see that the 1.25V reference gives and output span of 0V to 2.5V. The 2.5V internal reference gives a 0V to 5V output span. As with all our DACs, when these parts are configures for use with an external reference the total gain=1.

If we look at the table at the bottom of the slide we see that the DAC output is equal to the internal reference value gained/amplified by 2. The 1.25V reference gives an output span of 0V to 2.5V and the 2.5V internal reference gives a 0V to 5V output span.

Due to amplifier headroom reasons, we recommend that the devices with a 2.5V reference must operate between 4.5V and 5.5V supplies and devices with a 1.25V internal reference should operate between 2.7V and 5.5V supplies.

These parts can be configured for use with an external reference through software. it should be noted that this gives a different output gain. the output gain when using an external reference=1. For example, An external off-chip 3V reference gives an output span of 0V to 3V.

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  • I am presently working on a cct which has a Ad5660-1 nanodac on it.

    This device is powered from 3V and the vrefout is 1.25V. AD5660-1

    The Vout is 2xVrefout or 2.5V.

    I have noticed a peculiar problem.

    Whilst power cycleing the pcb and during other events, the nanodac reference can change from 1.25V to 2.5V. The output voltage Fs also changes.

    Even stranger though, I have a simple test waveform which counts from zero to full scall and repeats.

    during "normall operation , the output starts at zero and ramps to 2.5V and resets to zero.

    during "freakout" the output starts at zero, ramps to Fs/2 and then ramps down to zero.

    question.

    1)is there a sw mode switch to change the reference function (i cant see anything in the data)

    2) could this change in waveform hav something to do with 2s comp vs binary?

Reply
  • I am presently working on a cct which has a Ad5660-1 nanodac on it.

    This device is powered from 3V and the vrefout is 1.25V. AD5660-1

    The Vout is 2xVrefout or 2.5V.

    I have noticed a peculiar problem.

    Whilst power cycleing the pcb and during other events, the nanodac reference can change from 1.25V to 2.5V. The output voltage Fs also changes.

    Even stranger though, I have a simple test waveform which counts from zero to full scall and repeats.

    during "normall operation , the output starts at zero and ramps to 2.5V and resets to zero.

    during "freakout" the output starts at zero, ramps to Fs/2 and then ramps down to zero.

    question.

    1)is there a sw mode switch to change the reference function (i cant see anything in the data)

    2) could this change in waveform hav something to do with 2s comp vs binary?

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