> One of the products we interface with has an interesting way of doing
> level
> conversion - the first time I had seen something like this although it may
> be common.
>
> They used a tri-state buffer (or inverter depending on the desired output)
> having an enable line.  The input of the gate is tied to v+ or ground
> depending on the desired output.  The output to be shifted is connected to
> the enable line of the gate, and the gate's output is shifted output level
> with an appropriate pullup resistor.
>
> It's too early on a Saturday morning yet, so I hope the above makes sense.
> Sorry I don't have some typical part numbers as examples....
>
> Jon


One of my clients does this in their designs. This works as long as the
output is at a lower voltage (ie, chip driven by 5V and chip driving 3V
logic). When the chip is enabled, the output is pulled low. When the chip
is not enabled, the output floats and is pulled to 3V (or whatever the
pull-up is connected to) by the pull-up resistor. Note that if you use
this to convert 3V to 5V, you'd be pulling the chip output above the rail,
probably not a good idea for a tristate output.

I've used the Maxim level shifters a lot. They're really nice since you
can choose the number of drivers in each direction. One chip does it all.

Harold

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