DCDC UVLO question

I'm trying to design a DCDC converter with the Micrel MIC9130 and I'm having trouble figuring out how to choose the resistor values for the UVLO pin.

The datasheet is here

the UVLO is on pg 11

on pg 1 they have an example circuit with an input voltage of 36V-72V going to a voltage divider R1 = 1M and R2 = 38.3k, this is fed into the UVLO pin, so after doing the math the min and max voltages going into UVLO are from 1.328V to 2.59V

now, on pg 11, it says the line turn on trip point for the comparator is Vline_on = Vth * (R1+R2)/R2..... which after plugging in the values (Vth = 1.21V) I get Vline_on = 32.8V

the UVLO input range 1.328V to 2.59V will never get near this.... can anyone tell me what I'm missing here?

much thanks!

Den torsdag den 1. marts 2012 07.06.14 UTC+1 skrev panfilero:

The converter on page 1 is meant to operate between 36V and 72V. So it cannot have a ULVO of that range, need to set it below for it to operate from these specs. 1.22V on the UVLO pin is 33V on the line. So thats the trigger level

Regards

Klaus

nnot have a ULVO of that range, need to set it below for it to operate from= these specs. 1.22V on the UVLO pin is 33V on the line. So thats the trigge= r level

Ahhhh they're just working the voltage divider backwards to solve for Vin, thanks alot! makes sense now