How can I determine maximum load current limit of DC-DC step up switch regulator?
If you run TI's WEBENCH tool here.



Now with 1.6 A output current the design cannot be created because "Current exceeds limit". If you run the tool with output current set to 2 A, then an additional explanation will be shown.


  NOTE: The current ratings for boost parts are the peak switch current
  ratings, not the output current.  The switch current is dependent both
  on the output current and also on the amount of boost in voltage that
  is required in the design.  So for designs which require a large
  increase in voltage, the switch current is much greater than the
  output current.  Energy must be conserved by the following equation:
  
  \$ P_{out} = P_{in} \times Efficiency \$
  
  or
  
  \$ I_{in} = \large \frac{(V_{out} \times I_{out})}{(V_{in} \times Efficiency)} \$ which approximately =
  \$ I_{switch} \$
  
  For this design if we assume 85% efficiency:
  
  \$ I_{switch} = \large \frac{(5 \times 2)}{(3.3 \times .85)} = 3.57 A \$


For \$ I_{out} = 1.6 A \$ it would be \$ I_{switch} = \large \frac{(5 \times 1.6)}{(3.3 \times .85)} = 2.85 A \$ which still exceeds the maximum 2.1 A switch current.

With \$ I_{out} \$ unknown and \$ I_{switch} \$ 2.1 A, the maximum output current will be ~ 1.17 A.

The tool could generate the design with 1 A output current.