Now, it just read the differential value from the LTC2418.
You need to convert this value to the actual voltage.
It will be depending on the board.
You need to look for
what is the ref-voltage
what is the resister value
Where can you find that information? Look at the bill of materials (BOM) and schematics for the board.
The BOM can be used to find the resistor names in the schematics.
They are probably the only resistors on the board in the mOhm range. Now it will be easier to find the resistors in the schematic when you know which resistors you are looking for. You can then see which resistor is connected to which signal in the power monitor.
The power monitor probably has its own page in the schematic. You can also see the voltage connected to the monitor's VCC.
If the ref-voltage is 5.37V...
LTC2418 will give you 2^23 steps of value based on this.
so each step is 5.37 / (2^23)
You just need to multiply this step value to the differential value.
For example if the diff-value read is 0x06b6
1718 * 6.401538848876953e-7 = 0.0010997843742371
Now, the AMP is based on I = V/R
R value can be differ in each rail, most likley 1mOhm or 3mOhm.