Input Current for DC DC Converter
The factors that determine input current are output power, input voltage, and converter efficiency. Power = Voltage x Current. Efficiency = Power Out / Power In. If you know the converter's efficiency at the voltage and power it is operating at then calculating the input current is trivial. 

But...


  ...which has efficiency upto 90% at Minimum input voltage and 83% at
  Max Input voltage


That's a problem, because it only tells you the maximum efficiency the converter can achieve, not what it will be at any particular operating point. Efficiency typically peaks at less than rated output current. Here's an example:-

Pololu 3.3V, 1A Step-Down Voltage Regulator D24V10F3:-



At 5V this converter's efficiency peaks at ~93%, but is down to 83% at 1A out. At 24V it peaks at 83%, and is down to 79% at 1A. At 17V we would expect it to achieve about 81% at 1A. Now we can calculate the input current.

3.3V x 1A  = 3.3W out. 3.3W / 81% = 4.08W in. 4.08W / 17V = 0.24A.