INA240: Can INA240 to be used for precision low current measurement (0.1mA to 1A, VCM<5V)?

Hello Simon,

Thanks for researching TI products and posting to the forum. Unfortunately, a single INA240 will not be able to measure 0.1mA to 1A due to dynamic range. The 90uA IB certainly will affect accuracy on the low end of range, but even if you powered the INA240 with 5V and wanted to use its output range of 50mV to 5V, this results in a 100:1 dynamic range. The input current range you want to sense is 10,000:1.

A better current sense amplifier or current shunt monitor (CSA or CSM) would be the INA226 since it has a 10uV offset (Vos) max, 10uA IB, and a front-end, 16-bit ADC; however, only half this range can be used for unidirectional current sensing. Note this part is an I2C output device. So for your case in order to get a 10,000:1 input dynamic range out of the INA226 you would sense voltages from 8.192uV to 81.92mV. Unfortunately, 8.192uV is basically the same at the max Vos so you will not get anywhere near the accuracy at the low-currents, unless you precisely calibrate out this input offset, which would require more steps, instrumentation, lab equipment and would need to be performed for each individual device.

You could look into instrumentation amplifiers such as the INA114, but you will need to be careful in how you power the device so it can support a 5V common mode. Using TI's "Instrumentation Amplifier Output voltage vs. Common Mode Voltage" tools I did some trial and error and with a 30V Vs+, -5V Vs- and Vref =12V you can get an input dynamic range of -157mV to +167mV. However you need unidirectional current so if you go as low as the offset of the device (50uV), you still only have a dynamic range of 3,340:1.

You could look into using multiple amplifiers/sensors to split up the responsible ranges, but this will be expensive obviously on mass scale. If you would like to learn more options with instrumentation amplifiers, operational amplifiers, or transimpedance amplifiers please post to the following forums or look into previous/similar E2E posts:

https://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/t/667151

https://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/385110/1364990?keyMatch=precision%20current%20sense&tisearch=Search-EN-Support

e2e.ti.com/.../228733 measure

https://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14

https://e2e.ti.com/support/amplifiers/high_speed_amplifiers/

Hope this helps and post back if you need more information on the INA226 or other CSMs.

Sincerely,

Peter Iliya

Current Sensing Applications

Hello Simon,

Please know that we have recently released a current sense amplifier, INA190. It operates similarly to the INA240, but it has a much lower input bias current (0.5pA typical; 10nA max) so you could easily make 0.1mA current measurements. The output can only accurately go from GND+0.1V to VS - 0.1V and we recommend the highest Vs (voltage supply) to be 5.5V, but you could just barely measure the entire range of 0.1mA to 1A using two INA190 amplifiers. For example consider using two INA190s one with gain of 50V/V (INA190A2) and the other with gain 500V/V (INA190A5) and both powered with 5V. If A2 has a 98mOhm shunt resistor and the A5 has a 1 Ohm shunt resistor, then the INA190A5 will have a linear output of 50mV to 4.9V for the input current range of 100uA to 9.8mA. The INA190A2 will have a linear output voltage of 48mV to 4.9V for input current range of 9.8mA to 1A.

Sincerely,
Peter Iliya
Current Sensing Applications