Shunt current measuring on a negative voltage rail.. tricky?

[aSmallGuy]

I'm trying to read a current using a shunt resistor on the high side of a negative voltage. I found a lot of high side integrated current shunt ICs (ZTX 3 pins with current output are the best), but they all assume they are placed on the high side of a positive voltage rail, hence they have a high common mode voltage, but only positive to their supplied ground (terminology correct?).

Then I found this one, LT6105, where its Input common mode range extends 44V above V- indipendent of V+ (hence mobile).
http://cds.linear.com/docs/en/datasheet/6105fa.pdf



In this barebone schema I omitted the Load part with a ready current source. The current flows from ground to -40V, the shunt is in high side on the neg. rail (load is grounded, and the shunt resistor touches the voltage supply).

This looks like a huge life saver, the queston is: are there other similar chips? I was unable to find other components where the datasheet reported the input common mode range respect to V- (and the ability to have an explicit negative V-); to my untrained eye , they all reference to ground (in single or dual supply operations). A couple have something like -5/+60V, but it's not written if it's respect to absolute Gnd or V- pin applied voltage.

Second point, what if I have a -60V supply? Should I forcifully go with a differential opamp design like LT1990? (but then I will have to add a second amplifying stage).

I'm referring to Linear just because I have ready models in LTSpice to try (and the simulations actually converge); the bad is that it doesn't say if I'm violating component rating (max supply, common mode, etc).

Let me know if I got current shunts the wrong way 

[dom0]

The usual current sense amplifier circuit also works here; you can place the output load resistor on a positive voltage to get positive outputs (e.g. buffered ADC reference).

Edit: Attached image. ; gm = (Rg / Rf * Rs)^-1