AnsweredAssumed Answered

ADV7179 Power / Gnd plane

Question asked by KevinL Employee on Oct 28, 2010
Latest reply on Nov 1, 2010 by joe.triggs

a customer using the ADV7179 is asking about the power and grnd planes:

 

"If you look at page 39 of the datasheet:

http://www.analog.com/static/imported-files/data_sheets/ADV7174_7179.pdf

 

It is a bit confusing how the grounds should be connected.  The section “Ground Planes” suggests that all analog and digital grounds are treated as the same, though if you look under the “Power Planes” it says that the power supplied to this chip should be filtered through a ferrite bead and refers to this power as analog power.  To add to the confusion, the picture in Figure 54 suggests that there are analog grounds and digital grounds, but does not specify isolation.  Initially, our design treated all of the grounds as a digital ground and there was no isolation for these parts.  Now, a tid bit more information on the subject, last year I contacted Analog Devices and they said the thermal pad should be connected to digital ground.  This was different from other parts we used with our analog circuits which called for the thermal pad to be connected to analog ground.  If you can, please shed some light on this subject."

 

I have looked at the ADV7174/79 eval board schematic and also see ambiguous grnd symbols. Additionally, the eval board layout .pdf provided on the eval board CD is not the correct layout. Specifically, layers 2 and 3 do not match. There are major drill holes missing on layer 3 and many of the small drill holes are in different locations.

ADV7174_79 Evaluation Board - Rev. A - Layout.pdf

adv7174_79_eval_brd_schematic.pdf - Rev B version

ADV7174_79_EvalNote_260509.pdf

 

Message was edited by: AndyR: Removed customer board #.

Outcomes