Confusion about feedback resistor values for buck converter

Question

I'm making my first voltage regulation first with a buck converter, but I'm having some trouble making sense of the following datasheet. https://www.ti.com/lit/ds/symlink/tps560200.pdf

So I've made the circuit with the recommended components values given in Table 2 in section 8.2.2.2. Now I expect the table to give me the right results, but I did also gave equation 2 a try to calculate the R2 value.

I want an output of 3.3V, and I use the 20kΩ as recommended in the table for R1. This makes me end up with R2 needing a resistance of 6400Ω (=20000*0.8/(3.3-0.8)), but if I compare that with the 61.9kΩ recommended, then I get really confused as to how they arrived at those values, as those two values are nowhere near each other. Also, the equation of R2 seems to be inverted proportional to the values recommended in the table.

I would really appreciate an answer on what I'm doing wrong, as I, by default, assume I am as it's my first switching voltage regulation design.

Answer 1

Table 2 recommends that R2 be 20 k-ohms throughout, then gives you R1 values. This is backwards from how their equation 2 calculates it.

I get 62.5 k-ohms for R1 given 3.3V out and R2 = 20 k-ohms. I'm not sure where that discrepancy is, but it's a lot closer to their table.

Basically -- make the voltage divider that feeds the \$V_{sense}\$ pin such that \$V_{sense}\$ sees 0.8V when the output is what you want.