The output voltage range for BOOST is programmable with TWI. The default output voltage selection is defined by the VSET pin and is effective only at startup. A pin that is not connected configures VOUT to 3 V, and a grounded pin configures VOUT to 1.8 V.
Output voltage can be set in 50 mV steps in register BOOST.VOUT. Once the voltage is selected, register BOOST.VOUTSEL must be written to for the values to take effect.