SLVSAF7C September 2010 – April 2019 TPS61251
If VIN > VOUT the TPS61251 device offers the lowest possible input-to-output voltage difference while still maintaining current limit operation with the use of the 100% duty-cycle mode. In this mode, the PMOS switch is constantly turned on. During this operation the output voltage follows the input voltage and will not fall below the programmed value if the input voltage decreases below VOUT. The output voltage drop during 100% mode depends on the load current and input voltage, and the resulting output voltage is calculated using Equation 3.