LMZ34002: How to find the efficiency of LMZ34002 for an arbitrary switching frequency for which graph is not plotted in the datasheet

Hi,

I am using LMZ34002 to generate -5V output at 1.6A. The input to the system is a 12V rail and my switching frequency is 500KHz.

But the datsheet gives the efficeny curve only for 800KHZ switching frequency. 

So how can i accuratly calculate the input current requirement for 500KHz switching to meet the above requirment.

Thanks and regards
DEEPAK V