https://www.analog.com/en/resources/design-notes/add-high-voltage-capability-to-the-max471max472-highside-current-sense-amplifiers.html
Add High Voltage Capability to the MAX471/MAX472 High-Side Current Sense Amplifiers | Analog Devices
An avalanche diode and current source provide floating power supply to allow high-side current sense amplifiers to work at up to 300V.