Evaluating the Si8540 Current Sense Amplifier

I needed a current sensor for another project. I found the Si8540 in Mouser’s catalog. It requires a very low resistance sense resistor. The output voltage is in the zero to 3V range. The Si8540 comes in a SOT-23 package and costs US$0.55/piece in single quantities.

si8540I fabricated a prototype board that has holes large enough to solder 14 awg wires for load and source. Like most of my prototype boards, this one had a flaw in it (as seen by the jumper). Including the pcb, this board cost me less than US$2.00.




Using a current limited supply and some high wattage resistors, I compiled the data to chart the performance over a 3 amp load. The low of end of the current sense is skewed. The datasheet talks about the typical error at 1% of Full Load being 5% to 10%.

Si8540 calibration