Measuring current drawn on a 12V rail

I'm looking for a high side current monitor which can measure 0-3A on a 12V rail with either a built in sense resistor or with a hall effect current sensor. I'm also space constrained, to SOT-23 or so in size. Does anyone have any suggestions?

2 Answers

Maybe use an Allegro linear hall sensor, and lay out a current loop under the SOT-23 package? I haven't done the math. Use Ampère's Law and the sensor datasheet to see how likely this is to work.

• I've found a SOIC-8 sensor for 0-5A, which would be good enough, but it would be better if I could go even smaller. – Thomas O Nov 6 '10 at 12:18

Allegro is often a first choice for high side current monitors, but it appears they don't have anything smaller than SOIC, like the ACS712, CMIIW. This has the current sensor itself integrated, so it may compete with a SOT-23 solution.

For a SOT-23 you have for instance the Zetex ZXCT1009. This has a transconductance of 10mA/V; a short PCB trace could serve as current sensor. A 1cm zigzag trace 0.2mm wide then gives you 250$\mu$A/A, so a 1k$\Omega$ load resistor will result in 750mV full scale.