ADS1281 Best Layout for low noise

Hi,


Getting a good layout for a precision design is a difficult task and there's quite a bit of information involved in putting it together.

One place to start would be this presentation on layout on precision designs:

www.ti.com/.../slyp167.pdf

Also, there is a page on layout in the precision data converter notes with some more information.

e2e.ti.com/.../general-pcb-layout-questions.aspx

However, I find that one of the best resources is the ADS1281EVM-PDK. It has the schematic and a photo of the layout. It may be hard to read, but you can get some basic ideas on how the EVM was put together. Generally, the EVMs have been laid out to have the same basic noise performance as shown in the datasheet.


Joseph Wu

Hi,


I wanted to add a couple other comments.

First, if using a bipolar supply (+/-2.5V for AVDD to AVSS) use bypass capacitors from each supply to GND. It also helps to add another capacitor from AVDD to AVSS directly.

Second, when routing the reference (as an example using the REF5050 as in the EVM), route a line directly from the point where the reference is grounded to the VREFN pin. Don't just drop these pins into the ground pin. With any of the ground lines, you'll have return currents that could add additional noise. By routing the ground connections directly to each other, you can limit this effect.


Joseph Wu

Thanks Joseph.