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Altera_Forum
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13 years ago

JTAG/IO Clamping and Hot-swapping

I am putting Cyclone IV GX on a new board that will be configured using PS. Since all the VCCIOs are 3.3V, I am planning on clamping the the JTAG and PS config signals using a pair of schottkys betw...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
13 years ago

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Any clever ideas out there to deal with this?

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My personal preference is to protect JTAG and external I/O using Fairchild TinyLogic or TI LittleLogic parts.

http://www.fairchildsemi.com/products/logic/tinylogic/

You can power them from 3.0V, so you do not need the clamp diodes, and their inputs are tolerant to 7V when power is off, eg.,

http://www.fairchildsemi.com/ds/nc/nc7wz16.pdf

(http://www.fairchildsemi.com/products/logic/tinylogic/)

If you are designing your hot-swap system to correctly sequence power supplies, then these buffers can be part of that sequencing.

If you are plugging into a powered backplane, then you can use hot-swap buffers with a 1V bias voltage on their output. See the following schematic for examples:

http://www.ovro.caltech.edu/~dwh/carma_board/ (http://www.ovro.caltech.edu/%7edwh/carma_board/)

http://www.ovro.caltech.edu/~dwh/carma_board/gda06rb004_carma_v0.87_dec03.pdf (http://www.ovro.caltech.edu/%7edwh/carma_board/gda06rb004_carma_v0.87_dec03.pdf)

Cheers,

Dave