My guess is the original poster has misused the word powered.
The MCP42100 needs to be powered from the same power supply as the op-amp. Unfortunately the high threshold voltage is equal to 0.7*V
DD, which would be 3.5V, in this case, so a level shifter is required.
There's a small breakout board available or you can copy schematic off the Sparkfun website. Then there are ICs, such as CD4504, 74HCT126, 74HCT241, 74HCT244 (3.3V to 5V) and 74HC4050 (>5V to <6V).
https://www.sparkfun.com/products/12009