The MAX14662 is able to withstand voltages from -0.3V to 6V on the serial interface lines (i.e. /CS/AD0, DOUT/AD1, SCLK/SCL, DIN/SDA). As long as the signals are within this range the device will not become damaged. The serial interface engine is not active when Vcc is not connected. Please reference the "Absolute Maximum Ratings" section to ensure these specifications are not violated.