cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 
Anonymous
Not applicable
2,747 Views

Spartan-6 PCI Hot Swap

I am using a proprietary PCI backplane (3.3V signaling) that supports hotswapping and section 4.2.2.3 of the PCI 3.0 spec lists worst case overvoltage as 7.1V which is in excess of the Absolute Max input voltage for the IO pins.  The concern is that during hot-insertion a device like the Spartan-6, which does not have its PCI clamp diodes enabled until after configuration, will be exposed to large-swing signals.

 

Adding isolation devices like quickswitches, or external clamp diodes isn’t an option as the entire capacitance budget for each module is only 15.3pF(connector/routing/pin), and the worst case pin capacitance of the Spartan-6 is 10pF, which doesn’t leave enough wiggle room to accommodate the extra capacitance of these devices.

 

I need a solution that would allow hotswap in this environment without the potential for damaging the device.

Alternately, is there characterization data that shows worst case overshoot to be less than the absolute max Input voltage?

 

Is there any official statement that operation at these levels and conditions is acceptable, for these parts?

0 Kudos
2 Replies
eteam00
Professor
Professor
2,739 Views
Registered: ‎07-21-2009

Any device which has clamp diodes to VCC/O when unpowered is, by definition, not hot-swappable.

 

Spartan-6 is hot-swappable.  Look at the the datasheet (DS162), Table 1.  For commercial temp range parts, all IO pins tolerate voltages up to 4.25V (20% overshoot duration) or up to 4.1V (steady state) even un-powered.  This is your official answer, nothing more is needed.

 

For 3.3V PCI (or lower), quickswitch buffers and similar remedies are not needed.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
0 Kudos
jschimek
Xilinx Employee
Xilinx Employee
2,687 Views
Registered: ‎08-02-2007

You will not want to apply 7.1v to an unpowered Spartan-6 device.  Without the clamp diodes enabled (pre-configuration), you need to respect the DS162 specs.


I agree that the IOs do not require a Vcco voltage to withstand 4.1v (steady state), but to be tolerant to higher voltages, you will need the clamp diodes enabled, which requires configuration to be completed.

 

Regards,

Jon

0 Kudos