I have a circuit that outputs a digital signal to an FPGA on an XEM6310 board. To digitize the signal, a comparator is used with a reference/threshold voltage of +12 V, with its positive rail tied to +12 V and negative rail tied to GND.
The output of the comparator will switch between discrete values of 0 and +12 V. However, the XEM6310 can only tolerate voltages of ~4 V maximum. Furthermore, 3.3 V on the FPGA maps to a logic high, and 0 maps to a logic low.
I therefore need to level shift the +12 V output of the comparator down to 3.3 V. From my understanding of how fixed-direction level shifters work, you tie one pin of the IC to the voltage level that is being shifted (+12 V in my case), and the other to the desired shifted voltage (+3.3 V.) For the IC that I am selecting these pins are Vcc and Vdd respectively (DS states that Vcc can exceed Vdd.) Then, the input to the level shifter would be tied to the output of the comparator, where its output would map to the corresponding output pin of the IC (to be sent to XEM6310.)
My question: As I only want to perform a shift when the input to the level shifter is +12 V, what will happen when the input is 0? Will a shift occur or will the output of the level shifter match the input (since the input does not match Vcc)?
I do not want to shift the 0 output of the comparator as it is already at the required logic low for the XEM6310
I have attached a high-level image of the level shifter IC and a link to the DS: