USB port blew -- why?

From: larrymoencurly (larrymoencurly_at_my-deja.com)
Date: 10/04/04 

Date: 3 Oct 2004 18:18:44 -0700

One of the ports of my NEC-based USB 2.0 card quit working because the
National Semiconductor LM3526 power controller chip failed. I'm
pretty sure that I didn't zap it with static (I always touch the
outher metal shell to the computer case before plugging it in) or try
to plug it in backwards. The data *** for the LM3526 says that it's
protected against voltage, current, and even temperature, so what
happened?

National Semiconductor says that each USB port must have a 120uF or
larger tantalum capacitor between +5V and ground for protection
against transients that occur during hot-plugging, and NEC's example
schematic for their uPD720100A USB 2.0 chip shows the LM3526 using
150uF aluminum in parallel with 0.1uF ceramic. But my USB card has
only a 100uF aluminum capacitor and maybe a ceramic capacitor in
parallel for this. Could this be why the USB port got zapped? Would
it help to solder a tantalum in parallel as well? Will it hurt to add
it?

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