Extending a switch mode power supply controller IC to work under higher input voltages

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Extending a switch mode power supply controller IC to work under higher input voltages

I have a AP6502 IC, which is a cheap DC-DC buck converter. It converts a DC voltage in the level of 4.7V-18V to a DC voltage of 0.925V-16V. I works under 2A current maximum.

Example Usage of AP6502 given in its datasheet.

But, I have a much higher DC voltage level; it goes up to 100V. The output voltage will be 18V. And I want to flow 20A current at maximum. I want to extend/improve the example circuit above, so that this IC would work under higher voltages.

My attempt on this is the circuit below:

Is it possible to do this kind of extension? If yes, would my circuit work, is my solution correct? If my circuit is wrong, what is the correct way of doing it?