Achieving minimum output voltage with buck converter

[Abbott Daimler]

Hi, after searching the forum here, I couldn't find a similar question (at least not so that it answers mine). I'm hoping someone with experience in voltage regulators can help me.

I'm putting together a simple PCBA built around a three input DC/DC converter. The converter is the Richtek RT7273. The datasheet is here: http://www.richtek.com/assets/product_file/RT7273/DS7273-04.pdf and includes, on page 9, a simple schematic which is more-or-less identical to what I'm using for my PCBA.

The minimum voltage output for the RT7273 is 0.8v, which is exactly what I need for one of the three voltage ouputs. Setting the voltage output on this device only requires one resistor change and the formula for determining the resistor value is a simple one, R=40.2k x (0.8 / [V-Out - 0.8]).

This formula works fine with any voltage above 0.8v. However, how do I achieve the minimum voltage (0.8v) on the output? Do I simply remove the resistor-to-ground altogether?

Thanks so much for your help!

 

[Sunnysky]

yes that would agree on the formula.
then it becomes a unity gain Op Amp referenced to 0.8V

 

[Abbott Daimler]

Thanks Sunnysky! That's what I'll do, then. I appreciate the input.