Current monitor monitors low voltage spply current?

Hello,

On page 8 of the followiwng, fig 6 shows how LT1787 can be used to monitor current flow from supplys that are lower than 2.5V.

https://www.electro-tech-online.com/custompdfs/2013/07/LT1787_0999_Mag.pdf

How is this and why does it monitor from lower voltage supplys than fig 8 on page 9?

Look here https://en.wikipedia.org/wiki/Current-to-voltage_converter Figure 13. Thisis your basic current to voltage converter. It's output is Vout = -I*Rf.

If you add a voltage reference at the non inverting input, te output becomes Vout - Vref-I*Rf

So, you basically level shift the output with the 1.25V reference. The output is +-128 mV typically so you get an output range of 1.25-.0.128 to 1.25+0.128.