TXB0104: Floating inputs and bypass capacitors

Hey Jared,

Long story short - you can leave unused pins on the TXB0104 floating because they aren't really floating.

Also you can use a 0.22uF capacitor for bypass.

More info follows:

Each channel of the TXB0104 creates a weak latch -- the output on the 'A' side forces the 'A' input to the same voltage, which in turn outputs on 'B' and forces the 'B' input to the same level.  This is why the TXB series of parts has such a low drive current.  They have to be overdriven to change states.  This is also why you can leave the inputs floating.  They will be driven to a valid state automatically if not connected.

The value of a bypass capacitor is important, but it's  frequency response characteristics are more important for a bypass cap. I found a pretty decent app note from intersil here. Basically, over a frequency sweep, a capacitor acts like a capacitor up to a certain point, but at higher frequencies its inductive characteristics take over and it starts to look more like an inductor.

In general, having a bypass capacitor is better than not having one.  Having one that is the lowest impedance for the expected noise bandwidth is the best solution -- and sometimes that means having multiple parallel bypass caps.