ADS8555: ADS8555SPM

Heechang Lee

Prodigy 10 points

Part Number: ADS8555

Tool/software:

Hi,

I would appreciate your response. Thank you as always for your support.

I have some questions regarding the GND layout while designing a PCB based on the ADS8555 datasheet.

In the 2nd layer, AGND and DGND are separated as shown in the figure and connected at a single point. In this case, should the connection between them be explicitly made during the artwork process?
In the top layer, copper is poured in the dark-shaded areas shown in the figure. The copper seems to be connected to both DGND and AGND pads. In that case, how should this GND plane be defined?
Do the 20 vias in the center connect the top layer copper to both the AGND and DGND planes on the 2nd layer?

2 months ago

+1 Samiha Sharif 2 months ago

TI__Expert 8856 points

Hi Heechang,

Thanks for your question and patience as we were out of office for the US July 4th holiday.

There is some debate around this topic. Here is a good FAQ: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/755516/faq-pcb-layout-guidelines-and-grounding-recommendations-for-high-resolution-adcs

Generally, as long as you are physically partitioning or placing your analog and digital signals/components on different sides of the board (for example, digital to the left side in your case and analog to the right side), it is okay to share your ground plane without those notches.

If you look at the ADS8555EVM schematic and layout, we shared the ground plane and kept the digital signals separate from the analog.

The AGND and BGND pins in the ADC symbol itself should remain distinct to enable connecting analog and digital power rail decoupling capacitors to the respective ground pins.

Best regards,

Samiha

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ADS8555: ADS8555SPM