TLD5501-2QV: Voltage regulator, IN voltage lower than desired OUT volt
If the input voltage of the DC-DC is lower than the desired output voltage the device applies the Maximum BUCK Duty Cycle (P-6.5.2, data sheet).
Since the high side driver is designed for a NMOS, this parameter has a typical value of 92%. As a result the output voltage can be 0.92*Vin in such a particular condition.
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