LMR62421: LMR62421 with current sense resistor to FB pin and ground. Would this make a constant current driver?

I have done this with buck converters. One down side is the the FB voltage of 1.255 V will cause relatively large power loss in the resistor. Also for boost converter the available load current will vary greatly depending on the input and output voltages as it is proportional to (1-D).

Thanks for the response. I want to drive some LEDs and so the voltage needs to adapt to ensure constant current.

I was thinking of using a sense resistoer at the bottom of a 24V LED string. This resistor would connect to the feedaback pin. I am probably talking <100mA current through my LED string. So it probably isnt too bad a drain and would be a cheap solution. Possibly would hurt a little on efficiency but its cheap.

My thinking is that it would not matter on the input voltage. The output voltage would increase until the current was reached and hopefully stablise.

Trev

Yes, make sure you got the sense resistor sized properly for power. It looks like you need somewhere in the range of 10 ohm or so
Also you can put some kind of zener circuit for output voltage protection

Thanks
-Arief

Good call on the Zener. If I connect that between the output and the feedback it should limit max voltage. I was wondering how I could limit it.

Dev kit on order so we shall see.

I am wondering if I have an open circuit output will there be any risk of damage to the IC itself? I can't seem to find anything in the datasheet. 

When you say open circuit output means the LED got damaged? I think you need the output voltage protection. 

In this article, they use a zener as an overvoltage protection 

Also if you are interested on using a high side current sensing

Thanks

-Arief