Current monitoring is a critical function in a wide range of applications. In power supplies, for example, current monitoring is part of a closed loop system that regulates the power being delivered to a load. While ample, readily available current monitors exist today, a number of applications have current sensing requirements which cannot be met by monolithic devices in the market. Some of these requirements can include flexible gain, high speed, high common-mode voltage, and high impedance.

A current monitor that meets application specific requirements can be designed using a high voltage, high precision op amp such as the OPAx488 and the RESx1A series of precision matched resistors. The combination of the OPAx488 op amp and the RESx1A matched resistor pair enables a high impedance, high input common-mode, high precision current monitor to be built.

Use the following parameters for this design example:

• Power supply voltage rating: 48V
• Input common-mode voltage range: 48V
• Load current, I_L: 50A to 200A

The following design details and equations can be used to reconfigure this design for specific requirements.