The LT2940 measures a high side current and a differential voltage, multiplies them and outputs a current proportional to instantaneous power. Bidirectional high side currents and bipolar voltage differences are correctly handled by the four-quadrant multiplier and push-pull output stage, which allows the LT2940 to indicate forward and reverse power flow.
The circuit breaker application in the circuit above extends simple monitoring into the realm of control. The LT2940 is configured to measure motor current and power, and to protect the field magnets in the event the current exceeds the motor’s 8A rating. This circuit also highlights the use of the LATCH pin to keep the motor off after a triggering event until the RESET signal is pulled low.