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MAX4173 Current sense amplifier

I just built a current sensing application based on a MAX4173. I am suitably impressed with this device. It is extremely versatile and cheap. The MAX4173 allows you to measure the current across a sense resistor with a 28V common-mode range and provides a ground-referenced output proportional to the current across the resistor. I will probably be using one on most of my projects from now on since I do a lot of prototype work and having a cheap and easy way to sense current draw is pretty useful.

The MAX4173 is available in either an SOT23 or SO8 package, and only requires a decoupling capacitor and a sense resistor to operate. There are three different preset gains available so by combining that with the sense resistor value you can achieve a variety of current ranges.
I used the device in a 4-20mA control loop, with a 20X gain and a 10Ω resistor for a 0.8-4V output into an ATtiny 13’s ADC with a 5V reference. The 10Ω sense resistor is small enough that the loop won’t be affected and large enough to provide good signal range and sensitivity.
For future projects I will probably be using the higher gain version with a smaller sense resistor on the input power line and just leave the MAX4173 output on a header for diagnostic measurement if I don’t have a spare ADC pin. This will limit circuit loading but provide an output for measuring actual circuit current draw.
There is another similar version of the MAX4173, the MAX4080. It can handle higher common-mode voltages and bidirectional current. It’s also a bit more accurate than the 4173, but I haven’t tried it out yet.

Tags: Current sense, Electronics