# chosing the right Hall effect sensor

For a student project, I need a Hall Effect current sensor. What I am going to do is to charge 8 rechargeable Li-Ion batteries of 3.7 volts in series with 34 volt supply and the buck circuit frequency is between 5KHz to 10KHz. My concern is finding the right hall-effect sensor for calculation of the input current to adjust the current flowing to the batteries.

The batteries are 4000-6000 mAh and I am going to use AVR to sense the output of current sensor. So, I need a sensor with 5 volt output. I am thinking about finding the right current sensor for this circuit. ACS712ELC-05B is an example however, it senses 5A which is too high for this circuit and reduces the sensitivity of my measurement. I need something in safe range but not too far. Could anybody help me with finding a better option?

• How about a small resistor to measure current? – George Herold Apr 21 '15 at 12:12
• @GeorgeHerold not acceptable. btw, on resistor, both pins a floating (and with high voltage). – barej Apr 21 '15 at 12:25
• You could do a differential voltage measurement of the resistor with an opamp or instrument amp... 34 V is not what I would call high voltage. – George Herold Apr 21 '15 at 12:41
• @GeorgeHerold it is still high for damaging AVR. – barej Apr 21 '15 at 13:05
• Instrument amps have a reference output so you can put the output where ever you like... maybe an ina826? ti.com/lit/ds/symlink/ina826.pdf – George Herold Apr 21 '15 at 13:37

The LTC6102 is an excellent current sense amplifier. Its maximum offset voltage of $10\rm{\mu V}$ permits great accuracy, but it can only sense current in one direction. If you need to sense bidirectional currents and are willing to live with a bit more error, the LT1787 is a good choice, with $75\rm{\mu V}$ of offset.