Input pins without Vcco supply-- Virtex-II

[Jay]

Hi all,
The factory have made some mistakes when they had our V-II pcb board
manufactured and assembled. and we found only the Vccint, Vccaux and Vcco4
is available for the FPGAs.
To save time, we still want to do some debugging on this board before we can
get our new board.
Thanks god that with these 3 Vcc supplies we can download our design through
JTAG, and later I found input signals of other banks without Vcco still can
be used.(at least the GCLK, I've not tried other pins yet).
so my question is: can anyone confirm that I really can use the input pins
without Vcco. and how about its Electrical Characteristics, ?V tolerant etc.

 

[Austin Lesea]

Jay,

By using the banks that are unpowered as inputs, you are in effect
powering up the bankl by reverse biasing the protection structures
(diodes) that are part of the pmos output transistor stack (basically,
there is no separate diode, it is the junction of the pmos transistor
itself).

That said, the bank requires ~ 2mA to power on (as long as it doesn't
have to drive anything) so a bunch of inputs toggling effectively powers
up the bank....

Doesn't hurt anything at all. Can't say that we meet all specifications
for timing, etc. but you are certainly able to function.

In fact, the clock inputs are no different than any others, so you are
powering up the bank from those alone.

If you really want to power up the bank for test reasons, I would
program an output to be a "1" with the PCI IO standard (one of the
strongest) and themn connect that pin to 3.3V. That is good for ~ 60 mA
of IO current without concern. Need more outputs? Parallel up a bunch
of IOs as "1" to 3.3V.


Austin

Jay wrote:

Hi all,
The factory have made some mistakes when they had our V-II pcb board
manufactured and assembled. and we found only the Vccint, Vccaux and Vcco4
is available for the FPGAs.
To save time, we still want to do some debugging on this board before we can
get our new board.
Thanks god that with these 3 Vcc supplies we can download our design through
JTAG, and later I found input signals of other banks without Vcco still can
be used.(at least the GCLK, I've not tried other pins yet).
so my question is: can anyone confirm that I really can use the input pins
without Vcco. and how about its Electrical Characteristics, ?V tolerant etc.

 

[Jay]

Austin,

Thanks your answer. It sounds good!
That means we can use IO pins as power supply instead of Vcco.

"Austin Lesea" <austin@xilinx.com>
??????:bq2hma$ha33@cliff.xsj.xilinx.com...

Jay,

By using the banks that are unpowered as inputs, you are in effect
powering up the bankl by reverse biasing the protection structures
(diodes) that are part of the pmos output transistor stack (basically,
there is no separate diode, it is the junction of the pmos transistor
itself).

That said, the bank requires ~ 2mA to power on (as long as it doesn't
have to drive anything) so a bunch of inputs toggling effectively powers
up the bank....

Doesn't hurt anything at all. Can't say that we meet all specifications
for timing, etc. but you are certainly able to function.

In fact, the clock inputs are no different than any others, so you are
powering up the bank from those alone.

If you really want to power up the bank for test reasons, I would
program an output to be a "1" with the PCI IO standard (one of the
strongest) and themn connect that pin to 3.3V. That is good for ~ 60 mA
of IO current without concern. Need more outputs? Parallel up a bunch
of IOs as "1" to 3.3V.


Austin

Jay wrote:

Hi all,
The factory have made some mistakes when they had our V-II pcb board
manufactured and assembled. and we found only the Vccint, Vccaux and
Vcco4
is available for the FPGAs.
To save time, we still want to do some debugging on this board before we
can
get our new board.
Thanks god that with these 3 Vcc supplies we can download our design
through
JTAG, and later I found input signals of other banks without Vcco still
can
be used.(at least the GCLK, I've not tried other pins yet).
so my question is: can anyone confirm that I really can use the input
pins
without Vcco. and how about its Electrical Characteristics, ?V tolerant
etc.