1 Theory of Operation

In aerospace and defense, current sensing can be implemented in a variety of different applications. Whether it be for overcurrent and undercurrent detection for protection of systems, or monitoring current for telemetry for satellites and power supervision, or closed loop control in applications such as motors, current sensing is often a needed function. Often in these space-grade applications, it is necessary to measure currents in both directions thus needing a bidirectional device to accomplish the design goal.

For applications where only low-orbit space requirements are needed, the INA240-SEP device provides bidirectional current sensing capabilities with a single integrated circuit (IC). The INA240-SEP is Single Event Latch-up (SEL) immune to 42 MeV-cm²/mg at 125°C and total ionizing dose (TID) RLAT for every wafer lot of up to 20 krad(Si). Where higher levels of radiation requirements are needed for higher orbit applications, the INA901-SP is Single Event Latch-up (SEL) Immune to 75 MeV-cm²/mg at 125°C and Radiation Hardness Assured (RHA) 50 krad(Si) at Low Dose Rate. However, while the INA240-SEP supports bidirectional functionality, the INA901-SP only supports unidirectional sensing, and thus a challenge arises when bidirectional support is needed, but at a higher radiation hardness.

Since the INA901-SP is unidirectional, this application note explores how to design bidirectional circuits using an INA901 and additional components to achieve either a low-side or high-side implementation, and the associated tradeoffs with such a design.