For Virtex II:
Vbatt - in some places in the datasheet and user manual it is advised to leave it open if not used, in other it is advised to connect it to Vaux or to ground. Maybe someone knows what is the right way to go? (in previous project I left it open, no problems noticed).
DXN, DXP - can these pins be left open if not used?
-- Regards Robert
I've left these unconnected in multiple designs - no problems.
I leave these open with no problems. My understanding is that this is just a loose diode for temperature sensing. I've never checked if there is static voltage accumulated on them when left open. The only other reason to tie a pin off would be if it has an input buffer attached which could float to its threshold region - not the case for these pins.
Earlier versions of the datasheet indicated that Vbatt could be left open. The most recent version indicates that Vbatt should be connected to gnd or vccaux. Presumably this change was made to fix some problem.
Regards, Allan
The version currently on the web (ds031 v3.3) has this note on page 39: Notes:
What "most recent" version of the datasheet do you have?
All,
The question is: what to do with Vbatt if not used?
If it is not used, then it really is a 'don't care'. You could float it, connect it to ground, or connect it to a Vcco.
But if you let it float, it is a very low leakage pin (obviously, as you do not want to let the battery die from leakage).
A very low leakage pin is also a very sensitive pin to ESD damage.
So when we tested it for ESD, we decided to change the documentation to say to ground it if not used.
If it gets zapped by an ESD discharge, it will have bad leakage. It is most unlikely to cause any other problems, but why take the risk?
So, you are correct, in that we are correcting a problem. It is a very small, and very unlikely problem (customer removes part where Vbatt was left floating, Vbatt was zapped with an ESD discharge, and then uses it in an application where Vbatt is used, and the battery ends up running down in less than 25 years).
Aust> Allan Herriman wrote in
message news:...
.. and field replacement of a battery, where the Vbatt is much more physically exposed, is OK, or is High Risk ? - ie just what is the ESD rating of the Vbatt pin ?
-jg
Jim,
I knew it. I knew it! If I didn't put it in, someone would ask. I put it in, and then took it out.
All right, your correct: the ESD is rated at >500 V. But once it is soldered in, there is the circuit that we suggest to go with the battery, which includes two diode drops from the lithium coin cell, and a 0.1uF cap. The 0.1uF cap alone will limit the strike to much much less energy that it would be without the 0.1uF cap. The diodes will not help at all, but they might provide another path for discharge, rather than to the device.
(Thanks for keeping me honest),
Aust> Aust>
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