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Visitor general-zod
Visitor
19,447 Views
Registered: ‎08-02-2007

Question on: V5 GTP Power Rails

In Ch10 on page 193 of UG196 it states "Xilinx recommends the use of separate adjustable regulators for each supply circuit until full characterization results are available." 
 
Does that mean five separate regulators for MGTavcc, MGTavccpll, MGTavttrx, MGTavttrxc, and MGTavtttx? 
Have the characterization results been made available yet?  If not, when? 
 
I'd like to power MGTavccpll, MGTavttrx, MGTavttrxc, and MGTavtttx from one 1.2V (adjustable) regulator, and the MGTavcc from one 1.0V (adjustable) regulator.  
-=G. ZOD=-
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16 Replies
Visitor kamransays
Visitor
19,445 Views
Registered: ‎08-06-2007

Re: Question on: V5 GTP Power Rails


It is recommended to use separate regulators for each rail. You will also need to follow the correct power filtering that is described in the V5 GTP User Guide otherwise you may get noise on your rails that will cause your GTP performance to suffer.

Here is the the link to the Char report:
http://www.xilinx.com/xlnx/xweb/xil_publications_file.jsp?iLanguageID=1&ipoid=24368352&category=-1212269


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Newbie symon2
Newbie
19,421 Views
Registered: ‎08-07-2007

Re: Question on: V5 GTP Power Rails

Hi Kamran,
So, exactly why do you need separate regulators? Why can't you passively filter the noise? Do you know what the bandwidth of voltage regulators is?
Thanks, Syms.
p.s. What is the point of this forum? I think CAF is much more fun. Is swearing allowed here? What about aloud? Knobber chops.
p.p.s. So this guy goes "Doctor, doctor! I think I'm a moth!". The receptionist says, "OK, but this is a hairdressers." The guy says, "Yeah, I know, but your light was on."
p.p.p.s. I'll get my coat....
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Visitor k2says
Visitor
19,289 Views
Registered: ‎08-14-2007

Re: Question on: V5 GTP Power Rails

The transmitter is very sensitive to noise and there are very tight recommendations placed on how the power should be connected to the GTP. In the UG it out lines these better if you want more info on it. Basically if there is noise on the rails then you will get bit errors on the Receive side.
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Instructor
Instructor
19,263 Views
Registered: ‎08-14-2007

Re: Question on: V5 GTP Power Rails

That still doesn't explain the separate adjustable voltage regulators.  Is there some chance that the voltages will need to be different?  Or are they really just there as filtering components?  And if the voltages need to be the same (e.g. to prevent current loops flowing through the V5 from one supply to another) how tightly do you need to adjust all of these regulators?
-- Gabor
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Newbie srpen
Newbie
19,235 Views
Registered: ‎08-29-2007

Re: Question on: V5 GTP Power Rails

I went through the schematics for ML505 board. There are supply voltages for AVTTRX, AVTTTX and VTRXC pins taken from one regulator (its output node labeled AVTT), and some filtered by a LC filter (apparently those used), others directly. Therefore, only 3 regulators (AVCC_PLL, AVTT, AVCC_MGT - output node labels) are used
 
It would be very interesting for me if somebody could give here his experience with such arrangement.
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Xilinx Employee
Xilinx Employee
19,211 Views
Registered: ‎08-07-2007

Re: Question on: V5 GTP Power Rails

Hi All,
   It is fairly common for several GT rails to share an LDO, provided the following are true:
1)  Each power pin gets the correct voltage.  Stay as close to Vnominal as you can. 
2)  Each GTP power pin has its own bead + cap filter. 
3)  Make sure your LDO's can handle the worst-case load.

A few other notes on the subject.
1)  Coupling on the PCB is a common mistake that is easily avoided.  Be sure analog power planes are shielded by ground planes.  Take care to keep fast drivers away from power via's in the via filed under the FPGA. 
2)  In GTP, AVCCPLL and AVCC power analog circuits and need to be very clean.  Noise on these supplies will result in higher system jitter. 

-Mike W
Apps Engineer - Xilinx
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18,904 Views
Registered: ‎01-02-2008

Re: Question on: V5 GTP Power Rails

If noise is a major issue on these rails is using switching regulators to produce the rails a bad idea?

Looking at the ML555 schematic, page 31, the comments mention 3.5A on the AVTT 1.2V rail, 1.8A on the AVCCPLL 1.2V rail, and 1.8A on the AVCC 1.0V rail. But looking at the datasheet, DS202, page 9, table 14, I am assuming this for worst case:

AVTTTX 1.2V - 90mA per MGT_DUAL (6 on LX50T) = 540mA
AVTTRX 1.2V - 0.5mA per MGT_DUAL (6 LX50T)= 3mA
AVTTRXC 1.2V - 0.5mA per MGT_DUAL (6 LX50T)= 3mA

OR 546mA on the VTT rail.

AVCCPLL 1.2V - 60mA per MGT_DUAL (6 LX50T)= 360mA on the AVCCPLL rail.

AVCC 1.0V - 110mA per MGT_DUAL (6 LX50T)= 660mA on the AVCC rail.

Am I missing something?

Thanks,
Mike
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Xilinx Employee
Xilinx Employee
18,889 Views
Registered: ‎01-03-2008

Re: Question on: V5 GTP Power Rails

Using switching regulators for these supplies is not recommended.

We typically oversize the power supplies on the evaluation boards as you never know what someone may try to do with one of them and in some cases were are looking at sharing common components across multiple boards to increase the volume and lower the cost.
------Have you tried typing your question into Google? If not you should before posting.
Too many results? Try adding site:www.xilinx.com
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18,786 Views
Registered: ‎01-23-2008

Re: Question on: V5 GTP Power Rails

We use two Virtex 5 Chips connected together with GTP lanes over a very short distance of approx 1cm. Can we use the same Power Supplies (one for each AVCC_PLL,AVCC,AVTT) for all 8 GTP tiles (4 from one and 4 from the other V5 FPGA)?

Best regards,

Florian
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Participant doc
Participant
9,380 Views
Registered: ‎03-06-2008

Re: Question on: V5 GTP Power Rails

    sorry i can't respnd to your probleme but i want to ask you about something :
    My EDK9.1 don't containt a plb2opb Bridge  do you know where can i find this IP
Thanks,
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Visitor jnuckols
Visitor
6,045 Views
Registered: ‎07-17-2009

Re: Question on: V5 GTP Power Rails

I have an LXT V5 where the AVCCPLL is 1.2V. It's not clear to me from UG196 whether or not each voltage needs its own regulator -- particularly since at least one of the evaluation boards (ML50x) shares one regulator for MGTAVTTTX, MGTAVTTRX, and MGTAVTTRXC. For clarity, can I supply all 1.2V pins (MGTAVCCPLL, MGTAVTTTX, MGTAVTTRX, and MGTAVTTRXC) from a single regulator as long as I meet the three requirements in wissolik's posting?

 

Thanks.

 

Jeff N

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Xilinx Employee
Xilinx Employee
6,038 Views
Registered: ‎01-03-2008

Re: Question on: V5 GTP Power Rails

Yes. A single power supply is fine.
------Have you tried typing your question into Google? If not you should before posting.
Too many results? Try adding site:www.xilinx.com
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Scholar drjohnsmith
Scholar
6,029 Views
Registered: ‎07-09-2009

Re: Question on: V5 GTP Power Rails

The fundamental 'problem' is,

 

the serial links are all but impossible to debug.

 

you use one regulator and filtering, what do you do if the link does not work or even worse it 'tempramental'.

 

Now this could be 1001 reasons, it could well be noise on the MGT power lines, they are very suseotable to noise.

 

You end up like me with no finger nails in very short time.

 

It's because of this, and only this, that every one I know is VERY conservative with the power supply to the MGT.

 

Having said that, I've used switchers and filtering and it works very well, first time, 

 

but be carefull, and if you have the space / power / money, design conservativly.

 

 

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Newbie ceo30pjs
Newbie
5,167 Views
Registered: ‎04-23-2010

Re: Question on: V5 GTP Power Rails

 

Hi,
we are using GTP power in a Virtex-5 FPGA.

--ug196.pdf case 1 (page 231)------

MGTAVTTTX  = 1.2V
MGTAVTTRX  = 1.2V
MGTAVCCPLL  = 1.2V
MGTAVCC  = 1.0V
MGTAVTTRXC  = 1.2V  
------------------------------------

I'am miss take. a MGTAVTTRXC pin is not connected ("MGTAVTTRXC"= floating.)

How can I fix this? (hardware not Adjustment)

Thanks,

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Scholar drjohnsmith
Scholar
5,158 Views
Registered: ‎07-09-2009

Re: Question on: V5 GTP Power Rails

Hi

 

Do I understand you have a floating power supply pin,

 

Well, your going to have to modify the board to add the power I'm afraid, else the chip is going to be out of specification,

 

 

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Visitor jnuckols
Visitor
5,156 Views
Registered: ‎07-17-2009

Re: Question on: V5 GTP Power Rails

Do you have a floating power supply ball? If you have vias on all of the ball pads, and if your vias come all the way through the printed circuit board, then you can try adding a power connection to the via for the floating ball. Otherwise you'll have to try something more complicated like modifying the top of the board with the FPGA off, or drilling the board from the back side to get to the floating ball, etc.

 

Best of luck,

 

Jeff

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