High-Side Positive Current Sensor Monitors Negative Supply
Figure 1. Connecting this positive-supply-current monitor (U1) as shown lets it monitor a negative current while generating a positive output voltage for the ADC.
U1's current-source output drives a current that is proportional to load current flowing to ground (not to the GND pin). Output resistor RO converts the current to a voltage, which is then digitized by an ADC (optional):
The maximum output voltage is limited by saturation in the internal transistors (which occurs at approximately V+ -1.2V). Thus, V+ must exceed the full-scale output by at least 1.2V. If, for instance, the full-scale output is 1V, then V+ ≥ +2.2V. To meet the device's maximum and minimum operating voltages, 0 ≥ VEE ≥ -(32 - V+) and (V+ - VEE) ≥ +3V. Figure 2 shows the variation of current-measurement accuracy with load current.
Figure 2. The Figure 1 current-sensing error varies with load current as shown.