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I'm thinking of using a DAC as a precision voltage reference. I want 0-30V and would be happy with 12bit resolution although If i can get more I'd go for it.

My question really resolves around what DAC's will be best suited for this. DAC's typically run around 3.3V so I plan to use a opamp to increase this by a factor of 10x.

If I use a PWM DAC the noise/ripple would get amplified so that is out.

The use of a digital pot would be ideal although (as there is no noise) these typically cost more than a DAC though and have higher resolution.

I've seen a few audio DAC's around that have 24bits although I'm not sure if they will work with DC and what sort of ripple they might produce.

What DAC/type would you recommend?

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  • \$\begingroup\$ Just did a quick google, depending on how you plan to interface it you could use a Serial-DAC. Here's a 14/16bit 6v: analog.com/media/en/technical-documentation/data-sheets/… \$\endgroup\$
    – Nathan Wride
    Commented Aug 25, 2015 at 5:31
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    \$\begingroup\$ Something else to consider: your DAC will be no more accurate than its voltage reference. Pick a DAC which allows you to connect an external reference, and then choose a voltage reference accurate enough for your application. \$\endgroup\$
    – Synchrondyne
    Commented Aug 25, 2015 at 6:46
  • \$\begingroup\$ Another quick thought: you're using an opamp to increase the voltage and drop the output impedance, which is good. However, remember that the resistors you use for the opamp feedback network need to precision, and they need to be stable over temperature. A rookie mistake for RF power amp designers (or so I was warned) is to neglect this variation when designing biasing circuits, yielding a circuit which might operate just fine at room temperature and then go into thermal runaway on a hot day because the gate bias point changed. \$\endgroup\$
    – Synchrondyne
    Commented Aug 25, 2015 at 6:51

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I've recently looked at the AD5696 (quad 16 bit 0->2.5V output DAC) and the data sheet tells you this: -

  • INL and DNL add up to +/- 4 LSBs (+/-0.15 mV error in 2.5V full scale)
  • Zero offset is +/- 1.5 mV (2.5 volts FSR)
  • Gain error is +/- 0.1% of FSR (1.25 mV in 1.25V mid scale)

Total "mid-scale" error when extended to 10V full scale is 0.60 mV + 6 mV + 5 mV = 11.6 mV but this assumes a perfect amplifier following the DAC with perfect resistors. 0.1% resistors could give you an extra gain error of 0.2% but, MAXIM produce accurate and temperature stable potential dividers that are ratiometrically 0.025% so I'd consider them.

Also, as has been said in comments the voltage reference is paramount. You can get a voltage ref of initial accuracy 0.02% but of course this adds an error. Can you live with this unadjusted error?

Temperature and long-time drift account for significant errors. If you have a situation where the DAC is subjected to several degrees change in temperature then you have to look at the ppm/degC the gain might shift - the device above is +/- 1ppm/deg C so it's pretty good BUT you must still consider the error.

Ditto for the voltage reference - I am considering using the LTC6655 - it has an initial accuracy of 0.025% (which I will adjust) and a temperature stability of 2ppm/degC (max).

One final note if using a single supply DAC, check what the zero value eror is - this tells you how close to 0C the DAC will work - you might find that the bottom 5mV of range (or the top 5mV of range) are deadbands and unusable.

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