Need help to understand the consistency of Id in MOSFET datasheet

[staple123]

I have always tried understand the consistency of Id in many mosfet datasheets, I must have missed something.

For example in the datasheet I attached Si1422dh,

From the top in the Product Summary box, it lists 4 Rrs(on) values, with Id at 4A at given Vgs levels.


However, looking at the first chart, at stated Vgs levels, Id is inconsistent compared to the product summary box.


I understand the Product Summary Box is providing values for Rds, but given output characteristic, at those Vgs levels, the Id should be much higher. How can I reconcile the two?

Thank you very much.

 

[alexan_e]

The graph shows Id vs the voltage drop across drain/source.

For example the summary box says 0.03 ohm @ Vgs=2.5v and Id=4A ,
4A*0.03R=0.12v and that is the voltage you you will see in the x axis of the graph for the 2.5v curve @4A

 

[staple123]

Thanks for your reply. I thought when using mosfet as switches, usually they operate in saturated region, Vds and Id are determined by the load line from the circuit. Am I missing something? Could you elaborate? So Rds(on) only applies in non-saturated region?
Thanks again for your help.