DRV2700: Boost Voltage does not correspond to programmable voltage-divider

Tool/software:

Hi there, my circuit for outputting a steady DC boost-voltage (pretty much the same circtuit as "Figure 8-15. Boost Driving Piezo" from the datasheet) is not working properly.

The Potentiometer, which should vary the boost voltage, doesn't affect the boost voltage whatsoever. When turning it, the voltage on the FB-pin of the DRV2700 varies between 0.5V and 1V. But this voltage should be steady at 1.3V as I understand it?

The Boost-voltage output is connected to a op-amp circuit, to which no load is connected. (4x OPA455)

Thanks for any help!

Jakob