temperature sense diodes in Xilinx 7 series

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Has anybody used these?

We have two FPGAs on a board, a Zynq and an Artix7. We want to use the
internal ADCs to read chip temperatures. We have been advised to
ground the temp sense diode pins DXP and DXN "if they are not being
used".

Unless the XADC has a separate temp sense diode, seems to me that
shorting the external diode pins might kill our ability to acquire
temperature internally.

I don't see any big downside to not grounding those pins.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: temperature sense diodes in Xilinx 7 series
On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin

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After too much research, it seems that there are independent temp
sensors, the external-pin one and another inside the XADC.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: temperature sense diodes in Xilinx 7 series
On Fri, 03 Mar 2017 14:00:17 -0800, John Larkin wrote:

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And they recommend grounding DXP and DXN to improve the ESD rating.  IIRC  
there's no functional issue caused by leaving them open.

Regards,
Allan

Re: temperature sense diodes in Xilinx 7 series
On 04 Mar 2017 10:52:06 GMT, Allan Herriman

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Right, the esd thing makes no sense at all.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: temperature sense diodes in Xilinx 7 series
On Sat, 04 Mar 2017 09:29:14 -0800, John Larkin wrote:

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Why do you say it makes no sense?  A lot of devices have an improved ESD  
rating when their more sensitive pins are connected to low impedance  
sources (as opposed to being open).

Of course, if those pins are on a via-less pad under a BGA on a PCB with  
good planes, the difference may be hard to measure.

Regards,
Allan

Re: temperature sense diodes in Xilinx 7 series
On 05 Mar 2017 10:41:05 GMT, Allan Herriman

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Do you ground every unused pin on every FPGA?  


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: temperature sense diodes in Xilinx 7 series
On Wed, 08 Mar 2017 22:00:21 -0800, John Larkin wrote:

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Of course not, but I do ground pins that the manufacturer says to ground.

Last century (using QFP packages) I would sometimes ground extra IO pins  
to help with ground bounce on IO banks that had more O than I.

Allan

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