When the input voltage is higher than the setting output voltage, the output voltage is higher than the target regulation voltage, the device works in pass-through mode. When the output voltage is 101% of the setting target voltage, the TPS61033 stops switching and fully turns on the high-side PMOS FET. The output voltage is the input voltage minus the voltage drop across the DCR of the inductor and the R_DS(on) of the PMOS FET. When the output voltage drops below the 97% of the setting target voltage as the input voltage declines or the load current increases, the TPS61033 resumes switching again to regulate the output voltage.