A current shunt monitor, CSM, circuit for monitoring a current through a sense resistor disposed proximate a high side of a voltage input, the CSM circuit comprising: a voltage sense circuit having first and second inputs (212, 215) connected across the sense resistor on opposite sides thereof and an output for providing an amplified analog output signal proportional to a voltage across the sense resistor, the voltage sense circuit including an analog circuit with analog circuit components having a voltage rating that is less than a highest rated voltage on the voltage input; a power supply, including: a fixed voltage power supply configured to provide a fixed voltage output operating at a first voltage supply level relative to a system ground reference, a floating power supply operating at a second voltage supply level referenced from a voltage on the voltage input and a floating ground, a voltage supply level of the floating power supply configurable to be maintained at the second voltage supply level as the voltage input varies from a first voltage level above the first voltage supply level to a second voltage level within a predetermined voltage range of the first voltage supply level, and the floating power supply providing power to at least a first portion of the analog circuit at least when the voltage level of the voltage input is above the first voltage supply level by the predetermined voltage value, and a crossover circuit configured to switch power to the at least a first portion of the analog circuit from the floating power supply at the second voltage supply level to the fixed voltage power supply at the first voltage supply level upon detecting that a voltage level on the voltage input is within the predetermined voltage range of the first voltage supply level. a voltage sense circuit having first and second inputs (212, 215) connected across the sense resistor on opposite sides thereof and an output for providing an amplified analog output signal proportional to a voltage across the sense resistor, the voltage sense circuit including an analog circuit with analog circuit components having a voltage rating that is less than a highest rated voltage on the voltage input; a power supply, including: a fixed voltage power supply configured to provide a fixed voltage output operating at a first voltage supply level relative to a system ground reference, a floating power supply operating at a second voltage supply level referenced from a voltage on the voltage input and a floating ground, a voltage supply level of the floating power supply configurable to be maintained at the second voltage supply level as the voltage input varies from a first voltage level above the first voltage supply level to a second voltage level within a predetermined voltage range of the first voltage supply level, and the floating power supply providing power to at least a first portion of the analog circuit at least when the voltage level of the voltage input is above the first voltage supply level by the predetermined voltage value, and a crossover circuit configured to switch power to the at least a first portion of the analog circuit from the floating power supply at the second voltage supply level to the fixed voltage power supply at the first voltage supply level upon detecting that a voltage level on the voltage input is within the predetermined voltage range of the first voltage supply level. a fixed voltage power supply configured to provide a fixed voltage output operating at a first voltage supply level relative to a system ground reference, a floating power supply operating at a second voltage supply level referenced from a voltage on the voltage input and a floating ground, a voltage supply level of the floating power supply configurable to be maintained at the second voltage supply level as the voltage input varies from a first voltage level above the first voltage supply level to a second voltage level within a predetermined voltage range of the first voltage supply level, and the floating power supply providing power to at least a first portion of the analog circuit at least when the voltage level of the voltage input is above the first voltage supply level by the predetermined voltage value, and a crossover circuit configured to switch power to the at least a first portion of the analog circuit from the floating power supply at the second voltage supply level to the fixed voltage power supply at the first voltage supply level upon detecting that a voltage level on the voltage input is within the predetermined voltage range of the first voltage supply level.