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DAC7563: Power supply rejection ratio

Chip Weller
Prodigy 150 points
Part Number: DAC7563

I have a design which uses a DAC7563 to output a DC voltage used in a signal processing application. Noise on this voltage, especially around 2 MHz can effect our measurements.

There if a simple LC filter on the AVDD (3.3V) supply is adequate, or if we should add a separate low noise LDO to generate AVDD for this DAC.

What I would like to have is a graph of the power supply (AVDD) rejection ratio (PSRR) against frequency, which is common for op-amp datasheets.

My expectations is the PSRR should be good because of the VREF regulator. I have seen the VREF typical Line regulation at 25°C specification of 50 μV/V. Is this only for DC or is it valid at 2 MHz?

Thanks

  • 0
    TI__Mastermind 46290 points
    Hi Chip,

    The line regulation specification for the internal reference for this device is a DC PSRR specification - so only valid at DC.

    Some of our products do publish a curve for AC PSRR, but that's largely implemented in the newer datasheets. I will have to look internally to see if any curve exists for the DAC7563 and get back to you. Please give me a couple of days for that.

    What I can offer in the short-term is that typically PSRR has rolled off by 1MHz to ~10dB and stays fairly flat from there. I would not expect anything significantly different for this device. In the case of our device datasheets typically this curve is basically published just for the signal chain / output stage and uses an external reference. I'm not sure that I've seen the same kind of curve ever published for an internal reference.
  • 0 in reply to Kevin Duke
    TI__Mastermind 46290 points

    Chip,

    Here is what I was able to find:

    I believe that the behavior with the "dip" near 500kHz is a measurement anomaly or error in the setup that was used to collect this data, and potentially why the group at the time decided not to publish it. Otherwise my previous comments would look to likely hold up that the PSRR is going to be in the ballpark of -10dB (actually a bit lower in this data at -6dB) from 1MHz and beyond.

    Quite likely the LDO approach, and potentially an output filter, would be worthwhile in your design in my opinion.