Current Sense Amplifier Error when using negative voltage

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
I'm using INA210 current sense amplifyer. It works when the voltage source V1 is positive in the below image. But when it is negative, something weird happens and seems like.
Positive voltage case:
1660990645421.png
Negative voltage case:
1660990632577.png
So, what may be my problem?
 

DickCappels

Joined Aug 21, 2008
9,317
@Nabil Miri 's point it that
The maximum negative common mode voltage is -0.3 Volts. Any more negative is trying to operate the part beyond its specifications.

You can use a negative power supply to extend the negative range. It doesn't take many parts and is not expensive. One method is the ICL7660 one chip, three capacitors.
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
Ohhh now I understood it. I thought that I cant add a negative supply as it is connected always to GND in the datasheet. Thanks.
 

ericgibbs

Joined Jan 29, 2010
16,370
hi,
I see you have +22V supply, the max is +20V.

Could explain exactly what you are trying to do, so that I can understand your problem.
E
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
I want to build a current sense circuit to measure a current in my main circuit that changes from 1 mA to 1A (both directions). So, can you recommend any current sense amp that could help me do it. The common mode voltage range is +-22V.
 

DickCappels

Joined Aug 21, 2008
9,317
I am sorry, I should have been more explicit in explaining what we recommend.

What me mean is that it looks like you should connect you REF in to ground (if that is what you want to output to referenced to) and the negative power supply and then the ground pin can be connected to a negative voltage supply.

The total voltage between the ground pin and the + power supply pin cannot exceed the specifications as @ericgibbs pointed out in post #9, above. Be sure you are using the version of the datasheet that relates to your particular part.

A negative power supply would allow your output to swing about of below ground. If you are running through and A-to-D converter that has a range or, for example, 0 t0 5 volts then you should connect REF in to +2.5V, in which case you would not need a negative power supply.

A lot of things to think about. You don't want either end of your signal to clip, so
 

DickCappels

Joined Aug 21, 2008
9,317
I want to build a current sense circuit to measure a current in my main circuit that changes from 1 mA to 1A (both directions). So, can you recommend any current sense amp that could help me do it. The common mode voltage range is +-22V.
I think what I would do in this case is add some resistances in series with the input pins. Otherwise, a simple solution is to drive each input pin through a voltage divider to keep the common mode voltage within specifications. Either of these will change the gain and might require trimming for accuracy during production.
 

DickCappels

Joined Aug 21, 2008
9,317
After thinking about this a bit, you are apparently using the wrong INA. It would be a far better design if you were to find an INA that could handle the rather huge common mode input range, otherwise you would have to live with a patch.
 

ericgibbs

Joined Jan 29, 2010
16,370
hi Nabil,
Built this LTS model of INA271 from a Spice model, it checks out OK as far as I have tested it.
I have applied a 100mV test signal and I see 2V, as the model has a gain of 20.

E
EG 1345.png
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
Thanks for trying to simulate it.
BTW I am trying to simulate it in microcap but something maybe wrongly connected.
1661007118825.png
BTW my main issue is that the common mode voltage range is prefered to start from -22V
 
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