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my question is a bit specific, I have done the research but I got confused.

I am trying to measure the current using current sense resistor and a current sense amplifier INA 210 . my measurements will be taken using a 5V ADC( arduino). and I will be having 5V power supply to power up the ADC and the op-amp.

I want to measure current from 0- 0.5 amp, and lets say my op-amp gain is 100. so I have a chosen a current sense resistor of 0.1 ohm so when the current is max 0.5 amp, the voltage across the resistor will be 0.5 amp*0.1 ohm = 0.05 volt and when amplified amplified it will be 5 volt which is the full range of the op-amp.

that is okay but then I figured that the output of the op-amp will not swing to reach the supply voltage as it will reach bellow the 5 V supply voltage and it won't reach 0 volt which is my system ground.

my questions are: 1- I got confused getting the maximum and minimum output ranges and here are two pictures of the values I suspect, which one is true?

enter image description here

and here is the second picture:

enter image description here

2- second question is , if the second picture is the case, how to solve this problem? I mean this way I want be able to read the higher voltages above the op-amp range and the lower voltages bellow the other end of the op-amp output ranges

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    \$\begingroup\$ One of them is what the opamp is capable to do, and one is what you are allowed to do with its pins. \$\endgroup\$
    – PlasmaHH
    Feb 3, 2016 at 12:35
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    \$\begingroup\$ ... without damaging it. Maximum ratings: what can you safely apply externally. Electrical Characteristics: what can the IC do by itself. \$\endgroup\$
    – Bimpelrekkie
    Feb 3, 2016 at 12:37

1 Answer 1

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Best option will likely be to adjust the feedback resistor on your op amp so that you can accurately measure from 0-0.5A using voltage range 0.05-4.8 that the op amp is guaranteed capable of.

No amplifier that I'm aware of can operate at steady-state at or beyond it's "rails" (although there are several AC amps that can momentarily do that).

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  • \$\begingroup\$ this op-amp has a fixed gain. its designed this way because this will reduce the error if normal resistors are to be used to set the gain \$\endgroup\$
    – Sabir Moglad
    Feb 3, 2016 at 13:12
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    \$\begingroup\$ In that case, maybe the best option would be to get a slightly smaller value current-sense resistor, maybe 0.095 would work. \$\endgroup\$
    – Robherc KV5ROB
    Feb 3, 2016 at 13:21
  • \$\begingroup\$ Often the inputs can go outside the rails by 150mv or so on the low end and still have normal functionality \$\endgroup\$
    – Scott Seidman
    Feb 3, 2016 at 15:44
  • \$\begingroup\$ @SabirMoglad: IN210 is a fixed gain, but there are part nos available in the same IN21x series with different gain. Or may be powering he op-amp with 5.25V can guarantee the output close to 5.0V which 0.2V less (worst case) as per specs. \$\endgroup\$
    – AKR
    Feb 4, 2016 at 4:20

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