Instrumentation Amplifier Level Shifter
You can use an op-amp to generate -1.7V from the 2.50V reference. Most instrumentation amplifiers require a low impedance input for the reference input. 







simulate this circuit &ndash; Schematic created using CircuitLab

If the op-amp has very low bias current you may not need R1. Of course the op-amp requires a negative supply for this to work.