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ADS9218: 1V8 DVDD vs 1V8 AVDD

Austen Royer
Prodigy 140 points

Part Number: ADS9218
Other Parts Discussed in Thread: ADS9219EVM, ADS9219

Tool/software:

Hello.

I am looking at the ADS921x datasheet (revision SBASA74B - May 2024), and am confused by the discrepancies describing whether or not the ADC needs a separate analog 1v8 rail from the digital 1v8 rail.

The device block diagram on page 1 only calls out a 1v8 Digital and a 5V analog rail:

Next, the power supply recommendations section (figure 8-10) mentions a separate AVDD_1V8 rail, and calls out pin groupings of pin 13/14 for one 1v8 rail, and pins 35, 36, and 37 for the other 1v8 rail, but doesn't mention which is digital and which is analog:

 

Finally, I checked the ADS9219EVM schematics, and they show that the schematic symbol for the ADS9219 has different digital and analog 1v8 rails, but they are powered by the same 1v8 rail on the board. I noticed that these groupings were also different from the groupings called out in figure 8-10 of the power supply recommendations section of the datasheet, as they are pins 13 and 37 for one rail, and pins 14, 35, and 36 for the other rail.

My questions are:

  1. Does the ADS921x family have different power rails for 1v8 analog and 1v8 digital?
  2. If so, what pins on the device are used for the 1v8 analog rail, and what pins are used for the 1v8 digital rail?
  • 0
    TI__Expert 6700 points

    Hello Austen, 

    Thank you for posting on TI's E2E forum!

    Yes, the ADS92xx family of devices internally does have 2 power rails at 1.8V, one for analog and the other for digital. However, distinction between them is not necessary and they can both be supplied by the same power source and the device has the 1 ground. 

    In the initial stages of releasing this family of devices the distinction was made as you can see in the ADS9219EVM schematic as well as some remnants unintentionally left behind during some of the datasheet revisions. Even then it was still expected and recommended for them to be supplied by the same source (with the option of different sources). If different supply sources are still wanted, please follow the ADS9219EVM pin out.

    As the release of the devices progressed it was found that grouping both of these rails as "VDD_1V8" was a better option, we are working to ensure that is reflected throughout to avoid any further confusion. Apologies for any confusion it has caused. 

    Best regards, 

    Yolanda