10μA-10mA Low-Side Current Sensor

This single-supply, low-side, current-sensing solution accurately detects load current between 10μΑ and 10mA. A unique yet simple gain-switching network was implemented to measure the three-decade load current range accurately. The linear range of the output is from 100mV to 4.90V. INA326 instrumentation amplifier is used since low-side sensing is desirable because the common-mode voltage is near the ground. Therefore, the current sensing solution is independent of bus voltage, which allows for using single-supply, rail-to-rail input/output (RRIO) amplifiers. Low-side current sensing places a shunt resistor between the system load and the ground. The current drawn by the load generates a voltage across the shunt resistor. The output voltage of the circuit is equal to the current sense across the shunt resistor and the gain of the amplifier. A high-value resistor is used as a shunt for accurate current sense. It is advisable to use 0.1% tolerance shunt resistor R2.