LM5116: Minimum input voltage for stable output

Part Number:LM5116

Hello, I have made the boards with LM5116 (9-18V input, 7.5V output) and they are working fine, however with lower input voltages the output voltage drops.

For 9V I get around 6.8V output instead of 7.5V, if I go below 9V it drops even further. The current consumption is rather low (a few amps).

What may be the reason for this ?

What is the minimum input voltage that should ensure nominal output voltage ?  I know linear regulators have a defined voltage drop IN-OUT but how is the situation with such a DC-DC converter ?

And what happens if the input voltage is very low (for example 6V) - if the UVLO is not used ?

The output should follow the input voltage or it will drop further or what will happen ?

Thanks,

Mihai