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Re: PCI Hot Swap
In message <199609171257.IAA18622@cepheus.matrox.com>, Phil Cupryk
<Phil.Cupryk@Matrox.COM> writes
>
>Since my input buffers are not 11Volt tolerant, I opted to place clamping
>diodes to limit the overvoltage. However, in a hot swap situation, before
>insertion into a live system, the board's Vcc input to the logic gate is at
>ground potential. During insertion, when the pins make contact, the bus line
>is clamped to ground through the overvoltage clamping diode to Vcc. This in
>effect can cause the diode to conduct, thus allowing large currents to flow
>through the diode, resulting in the logic gate to latch up and possibly
>destroy itself when the power is finally applied.
The obvious answer is to clamp to a zener or transorb type device,
rather than to VCC.
I use AVX "Transguards" to protect a different circuit to about 7V. For
11V, depending whether you want to clamp below or above 11V, you may
have some difficulty, as the devices seem to come at 5.8V and then the
next is around 12V. General Instruments and SGS do similar devices.
Hope that is useful
--
Paul Walker 4Links for technical help
+44 1908 566253 P O Box 816, Two Mile Ash
paul@walker.demon.co.uk Milton Keynes MK8 8NS, UK
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