I'm in a bit of a pickle here. I need to translate 3.3v to 5v ttl levels. The devices I'm driving (12 total) are not low current devices so I don't want to interface directly, even with a current limiting resistor.
This is a reference design that I plan on selling and I want it to be as fault tolerant as possible. My first pass was just to add 100Ohm resistors across each output from the microprocessor (3.3v output). I'm rethinking that however and I was looking at voltage translation. The two techniques that look most promising for me is either a pass through transistor interface using a MOSFET such as bs170 and the other is to use a dedicated chip such as the TXB0108 voltage translator.
Here is my conundrum. I really want to keep the cost of these boards down. I've sourced the mosfets at mouser for about .25$ each when buying in lots of 100. The voltage translator ic's are a bit more expensive at about 4 bucks each, when bought in large lots. My biggest issue is I only need 12 pins to be translated so it seems on the second IC I would be wasting 4 pins. The mosfets are going to cost about 3 bucks per board (way less than the IC's) with a couple of resistors it brings up to 3.10 or so. So, that cuts my BOM cost by about 6 bucks, but my issue is the space on the board. Those 12 mosfets (and accompaning resistors) take up WAY more room than the two ICs (which take no external components).
TLDR; Does anyone know of another (cheaper and less room) than the two methods I mentioned above? I need to translate 3.3v up to 5v. It will only be output since the signal is unidirectional (always 3.3v -> 5v).