ADS1278 Grounding

Yashas

Other Parts Discussed in Thread: ADS1278

Hi,

I am using two ADS1278s daisy chained on a board and I don’t have the AGND and DGND connected on the board, it is happening somewhere outside. Oddly though, I still get only 5 ohms between AGND and DGND when I expect to see at least 1Mohm. If I pull out the ADCs, then AGND and DGND are open. So I tried ohming the pins of the ADS1278 stand-alone and I don’t see a 5 ohms path between AGND and DGND. Any idea whats going on? In my system the grounds are connected together on a separate power section board.

over 9 years ago

0 Joseph Wu over 9 years ago

TI__Guru* 92715 points

Yashas,

Looking at the ADS1278 datasheet, in the absolute maximums table on page 2, the maximum voltage between AGND to DGND is 0.3V. This implies that there are likely some low impedance path between the two. I would guess that it may be some ESD diode, or connection through the epi, diffusion, or junction on the chip itself.

I would have expected more than 5 ohms though, but it may depend on how many devices you daisy chain together.

Joseph Wu

0 Yashas over 9 years ago in reply to Joseph Wu

Prodigy 160 points

Joseph,

I later on found out that AGND pin 58 has only 10ohms connection to DGND pins 21,24,25 and since I have two ADCs I see 5 ohms. This poses a problem in my system because it can create a loop in analog and digital grounds with 0.2ohms off board and 10ohms on board connections. Is there a way around it to get a single analog-digital ground connection? Can I keep pin 58 open?

0 Joseph Wu over 9 years ago in reply to Yashas

TI__Guru* 92715 points

This forum post is now answered in this thread:

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/366773/1295011.aspx#1295011

Joseph Wu

Data converters

Data converters forum

ADS1278 Grounding