Ways to verify functionality of level shifter?

[bhj99]

Hi all, I would like to seek advice on the best and most straightfoward way of verifying the voltage translation functions of a level shifter part on a test backplane PCB design prior to mating boards together. The level shifter part used to convert SPI signals between a mezzanine board at 3.3V logic level and an FPGA at 1.5V logic levels is SN74LXC8T245 from TI. Schematic snippet attached for reference. I would like to avoid damage of downstream devices during component level testing/checkout, but having to lift output source-series resistors can be a pain to isolate just the level shifter. Would a simple way to test 3.3V -> 1.5V be to use a power supply or signal generator to inject these logic levels at the input port and probe at the output port? Any recommendations are welcome.

[moffy]

If the test backplane is completely separate you could test as you have suggested.

[bhj99]

Can you think of any simpler test approaches?

[ajb]

Why would you need to lift the series resistors? If the signals are going to/from a mezzanine board, then surely you can just inject/measure at the mezzanine connector before fitting the board? 

In general, yes, you can perform functional testing on parts like this by simply applying appropriate input voltages and observing the output voltages.  You could do that with a power supply, but be careful about leaving digital inputs floating.  Something that can provide appropriate logic level outputs would be preferable, even just an MCU dev board with appropriate connectors bodged on. 

[dobsonr741]

You can write a bringup code for the CPU to set one or more lines of the SPI high and observe. For example, CS would do. I would not verify all of the SPI lines, as the objective is not to verify the LCX245 is working according to the data sheet specs, rather to verify it's connected to the right power rail. That would be the most probable way this design can fail.