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DAC8811: MDAC in linear regulator feedback: will this work?

Marko Pavlin75965
Prodigy 140 points
Part Number: DAC8811
Other Parts Discussed in Thread: DAC9881

I would like to construct very clean microcontroller progrogrammable supply with output current max. 50mA and voltage range up to 32V. Main source is battery, which is boosted to 36V with DC/DC (LM7233), which is followed by linear post-reg to filter out ripple and stabilize output voltage at desired level.Output voltage range should be from 20V (0V not required, it is handled by enable of the DC/DC). Step size/resolution should be as small as possible.

I was thinking to place MDAC in feedback of a low noise/high PSRR linear regulator, something like this:

Is this idea OK ?

Thanks for any suggestions,

Marko

  • 0
    TI__Genius 14220 points
    Hi Marko,

    Thank you for your query. I am looking into your requirement. Due to the weekend and local holidays, I should be able to provide you with an answer by mid next week. Hope that is ok with you.

    You can look into this E2E post in the meanwhile: e2e.ti.com/.../give-your-voltage-regulator-the-margin-it-deserves

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    TI__Mastermind 46290 points
    Hi Marko,

    What you're describing at a high level, that is using an MDAC as a feedback element, is possible. We have done something like this in a TI Design for a variable filter: http://www.ti.com/tool/tipd160

    The only "gotcha" here is that the impedance of the MDAC from VREF to IOUT does not change by a huge value, so you may find that you do not have sufficient range to realize the output span that you desire.

    I would suggest that you instead use a more straight-forward approach with an amplifier offset to 20V, then use a 16-bit DAC (we also have the DAC9881, an 18-bit DAC since you mentioned "step size/resolution should be as small as possible") to provide you with the 16V span from 20V to 36V.