ZedBoard VCCAUX vs. VCBATT_0

[jude]

I am working on a solution to power the ZedBoard's BBRAM with a battery when the 12V supply is unavailable. Looking at page 28 of the HW UG, I only see VCCAUX which leads me to believe that the battery is powered by VCCAUX when the board is plugged in and switched on. On sheet 10 of the schematics I see VCCAUX and VCCBATT_0 both supplying powering the 1.8V rail. What I want to know is the following: If I connect a battery to BBRAM, will power be drawn from the battery at all times or only when the 12V supply is switched off? Please let me know if you need any more information to answer this question. Thank you!

[JColvin]

Hi jude,

I personally don't know the answer but I have asked some of our application engineers about this; they will get back to you here on the forum.

Thanks,
JColvin

[Alex]

I think you may be able to use VCCAUX which is the auxiliary voltage for the PL to power the BBRAM. Refer to the white paper from Maxim http://pdfserv.maximintegrated.com/en/an/REFD5449.pdf

[jude]

Thank you these schematics are informative. However, I am still left unclear as to the nature of the connection between header J16 and VCCAUX.

[mwingerson]

Hello Jude,

You have some challenging questions.  J16 is a header so a secondary battery can keep the security section of the RAM active without the primary 12V source.  To do this, R187 need to be removed otherwise the secondary battery will be powering a good chunk of the board and has a high chance of damaging some components.  In this case the amount of power that will be used through VCCBATT_0 pin should be very small.  I looked through the documentation but I could not find how much current will be pulled through VCCBATT_0 with or without a 12V source.  

I would suggest contacting Xilinx support or forums to find a more solid answer.

Best of luck,

Marshall

[jude]

This clears things up a bit more and you are right that I certainly have an involved question. It appears the solution to achieve the functionality I need is going to be a bit more involved than I anticipated. For now, I will look into the actual power requirements of VCCBATT_0, possibly testing them myself since I can not find this information in any Xilinx/ZYNQ documentation. Thank you for your help!