temperature sense diodes in Xilinx 7 series

J

John Larkin

Guest
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

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin
<jjlarkinxyxy@highlandtechnology.com> wrote:

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.
Click to expand...

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

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Fri, 03 Mar 2017 14:00:17 -0800, John Larkin wrote:

On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin
jjlarkinxyxy@highlandtechnology.com> wrote:

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.

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

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
 
On 04 Mar 2017 10:52:06 GMT, Allan Herriman
<allanherriman@hotmail.com> wrote:

On Fri, 03 Mar 2017 14:00:17 -0800, John Larkin wrote:

On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin
jjlarkinxyxy@highlandtechnology.com> wrote:

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.

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

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
Click to expand...

Right, the esd thing makes no sense at all.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Sat, 04 Mar 2017 09:29:14 -0800, John Larkin wrote:

On 04 Mar 2017 10:52:06 GMT, Allan Herriman <allanherriman@hotmail.com
wrote:

On Fri, 03 Mar 2017 14:00:17 -0800, John Larkin wrote:

On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin
jjlarkinxyxy@highlandtechnology.com> wrote:

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.

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

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

Right, the esd thing makes no sense at all.
Click to expand...

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
 
On 05 Mar 2017 10:41:05 GMT, Allan Herriman
<allanherriman@hotmail.com> wrote:

On Sat, 04 Mar 2017 09:29:14 -0800, John Larkin wrote:

On 04 Mar 2017 10:52:06 GMT, Allan Herriman <allanherriman@hotmail.com
wrote:

On Fri, 03 Mar 2017 14:00:17 -0800, John Larkin wrote:

On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin
jjlarkinxyxy@highlandtechnology.com> wrote:

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.

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

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

Right, the esd thing makes no sense at all.

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
Click to expand...

Do you ground every unused pin on every FPGA?


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Wed, 08 Mar 2017 22:00:21 -0800, John Larkin wrote:

On 05 Mar 2017 10:41:05 GMT, Allan Herriman <allanherriman@hotmail.com
wrote:

On Sat, 04 Mar 2017 09:29:14 -0800, John Larkin wrote:

On 04 Mar 2017 10:52:06 GMT, Allan Herriman
allanherriman@hotmail.com
wrote:

On Fri, 03 Mar 2017 14:00:17 -0800, John Larkin wrote:

On Fri, 03 Mar 2017 13:34:58 -0800, John Larkin
jjlarkinxyxy@highlandtechnology.com> wrote:

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.

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

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

Right, the esd thing makes no sense at all.

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

Do you ground every unused pin on every FPGA?
Click to expand...

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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