I need a suggestion on a good amplifier design for a current sensor. The requirement is:
Operating voltage between 2.7 to 6.0V
Able to output 3.3V when a 10A current is flowing through sensing resistor (maybe 0.011 ohm).
Able to output 1.65V when 5A and so on.
Able to output 0V when 0A.
Is this possible without a -Vs?
My source will be at ~30V
(It would be nice if it could handle voltages as low as 0.4V and current 3A also)
Best Answer
Using a high side current shunt solution would eliminate the need for a -Vs supply. Also, it is simpler to fine-tune the output to full-scale in a separate voltage gain stage, taking its input from the current shunt stage.
For example, using the Texas Instruments INA193 current shunt monitor:
simulate this circuit – Schematic created using CircuitLab
The nice thing about the INA193 is, with its common mode range being -18 to +80 Volts, it can be used as a low-side current shunt monitor as well, by switching the sense pins around and changing the shunt location, and not touching the rest of the circuit. It allows its output to reach not just the ground rail, but 0.3 Volts below it, without a -Vs pull-down.
INA193 has a fixed gain of 20 V/V. Thus, a 0.01 Ohm shunt resistor will provide an output range of 0 to 2.0 Volts.
The preset
Rtrimshown in the schematic can be adjusted to give an output of precisely 3.3 Volts on full-scale (10 Amperes) reading.Trimming the gain might be a good idea anyway, since a small imprecision in the shunt resistor would result in significant variation in full-scale output from the InAmp.
Note: 3.3 Volt output with operating voltage below 3.3 Volts is not feasible with this design: The maximum output will be limited by the Vcc supplied.
If a 3.3 Volt output at 2.7 Volt input is truly required, then an additional charge pump or boost solution would be required to raise the supply voltage of the TLV2372 to a minimum of 3.3 Volts.