ZedBoard - TSUB1210

[gge]

Hello
 
Thank you all for taking the time to read this.  I had a question on the Zedboard's use of the TUSB1210.  I know the Errata mentions the issue with the timing.  It seems now that the issue has been resolved by TI as they state the timing is within the Zynq timing requirements so that isn't an issue now.  Also it has worked for the Zedboard.
But I also saw another potential issue according to the TI TUSB1210 datasheet it states the VBAT voltage should be applied before the VDDIO voltage.  The VBAT on the Zedboard is connected to 3.3V and the VDDIO is connected to the 1.8V.  Looking at the power supply sequencing on the Zedboard the 1.8V comes up first than the 3.3V which follows what the Zynq datasheet outlines.  Unfortunately according to the TI TUSB1210 datasheet there is a diode between VBAT, 3.3V and VDDIO, 1.8V and if 1.8V comes up first there should be a problem.  Now obviously this doesn't seem to be an issue with the Zedboard but why?

 

Please any info or advise would be greatly appreciated.

Gary

[JColvin]

Hello,

I personally don't know the answer to your question, but I have asked some of our applications engineers to see if they can offer some insight into how this is working.

Thanks,
JColvin

[jpeyron]

Hi gge,

Good catch. You are correct that the VBAT(3.3v) should be on before the VDDIO(1.8v) based on the TUSB1211 recommented power sequencing. I have pointed this out to our design engineers and should make adjustments for this situation for future revs. My guess is that diode is forward biased and allowing current to the 3.3v rail until the 3.3v rail is powered on. Due to the lack of issues with the TUSB1211 on the Zedboard the time between the 1.8v rail and 3.3V rail being powered on must be short enough as well as a nominal amount of current that there is no damage being done to the diode.  

cheers,

Jon