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 above shows a core use of the LT2940, a simple power monitoring application. The circuit operates over a 6V to 80V range, measuring up to 240W. Below 24V the measurement range is limited to 10A maximum. The comparator output lights an alarm LED when the load power exceeds 60W. Owing to the bandwidth of the LT2940, even relatively short over-power excursions in the 2μs–3μs range are easily detected by the comparator.