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Separate LDO's for ADC08D1520 Analog and Digital rails

Reza
Intellectual 765 points
Other Parts Discussed in Thread: ADC08D1520

Hello,

I have used separate +1.9VA and +1.9VD LDO's for Analog and Digital power rails of ADC08D1520 to keep the digital and analog rails isolated and as clean as possible.

The absolute maximum (VD - VA) for this ADC based on datasheet is 0-100mV.

During system Power on I get higher |VD - VA| and that's something unavoidable because of seeing different loads on Analog and Digital rails of ADC, Capacitors and etc. I am wondering if this could hurt the ADC in long term or not?

Would you recommend to use the same power supply for VA and VD or keep them separated?

I have attached my ADC08D1520 power-on snapshot which shows +1.9VA and +1.9VD which are ONLY driving ADC power rails and nothing else is getting supplied from these LDO's.

Please let me know your comments.

Thanks,
-Reza

  • 0
    TI__Mastermind 44680 points

    Hi Reza

    In general where an ADC has multiple power buses at the same voltage I recommend that a single LDO regulator be used, with filter components to isolate the different buses from each other. That avoids any of these issues with power ramp timing.

    The voltage regulation circuitry on the ADC08D1520RB reference board is a good example. The design files for that board are available here:  http://www.ti.com/lit/zip/snar019

    The brief difference between supply voltages you are seeing could cause problems in the long term after many power cycles. In the short term I don't expect it to cause any immediate damage.

    If possible you should try using only one of the LDOs on your board instead of both. Since your board already has 2 LDOs you can check the performance with the current power architecture, and compare that to using a single LDO.

    Best regards,

    Jim B