Input offset current of INA214

MSP430;

Redrawing the basic circuit with discrete components will help understand what is going on in the INA214.

It is a difference amplifier, so we can use a precision op amp (selected arbitrarily) and four resistors with values specified in the INA214 data sheet. In TINA, a DC sweep of the input voltage from 1V to +3.5V reveals what is happening. Indeed, the currents do not have the same slope and change as you mentioned. By adding current probes to the inputs of the difference amplifier, one can see what causes these currents to vary with voltage.

Hi Neil, 

thx for ur reply. I could not open the file :( I dont know whats wrong with it.

Khaled;

Sorry-- I created that circuit using the industrial version of TINA, not the free TI version, so maybe that was the problem. In any case, I created a .PDF file of the TINA circuit together with the results. I hope this works for you.

Neil,

Thx a lot for the detailed simulation results.

Since I need to cover a range of 1V-3,5V of the input voltage, I think it doesn't make sense to use this part for current sensing, because of the jump of the current at around 2V...

MPS430;

I agree; If you are measuring only a few uA and can use only a 1 ohm shunt resistor (not more?), the INA214 is not the way to go.

I thought INA214 behaves this way due to its internal op amp. But when u simulated the same model structure using a random op amp, we observed the same behaviour. Could you igine what could be the reason of the voltage jump at V=2V?

thx

MSP430;

It isn't a "Jump", it is just the crossover point of two currents vs voltage curves with a different slope.

yes but I still don't understand the reason :(

MSP430;

Refer to the circuit that I posted previously. Note that AM4 = AM3 - AM2

When the input, V1 = 1V, the sign of AM2 is negative; the current is flowing from your Reference voltage through R1 & R4 in series, and adding to the current from AM3 into AM4. When V1 = 1.3V, no current flows from the Reference voltage through R1 & R4, because the voltage difference across them is 0V-- thus, AM2 is zero. Above 1.3V input, the current goes through R1 & R4 in the other direction.

A little time spent with TINA and a calculator will help you understand what is happening. I spent some time explaining the "negative input resistance" seen at the input of a difference amplifier as a function of its reference voltage in "The Instrumentation Amplifier Handbook".