LM339

[MAD MACRO]

I was reading this very interesting blog of how to work with comparator lm339: http://www.ermicro.com/blog/?p=1578

When using the feedback from the output, he has two equations to get the VLT and the VUT.

VUT = (R2 / (R2 + R1||R3)) x Vcc
VLT = (R2||R3 / (R2||R3 + R1)) x Vcc


now, i'm using this exact scheme to blink LED, and it's doing just that, it's working just fine.



My question is this: from where did he get that number "0.694" ?


I've tried to use those two equations of VLT and VUT and none of the results came close to 0.694.

[MAD MACRO]

got the answer from : http://bitsavers.informatik.uni-stuttgart.de/pdf/national/_appNotes/AN-0074.pdf

ln(0.5) = 0.6931