INA240: INA240

imtiaz khan

Part Number: INA240

Hi All

If a circuit using INA240 is powered by a battery can it then be used as an isolated current measurement device without regards to its common mode input voltage range?

Regards

over 6 years ago

0 Guang Zhou over 6 years ago

TI__Mastermind 34060 points

Hi IK,

No, that doesn’t make it an isolated device. You would want to use an isolated current sense amplifier or a magnetic technology enabled device.

Regard, Guang

0 imtiaz khan over 6 years ago in reply to Guang Zhou

Intellectual 440 points

Hi Guang

My question actually related to whether electrically the circuit would work or not. The word 'isolated' was merely used to describe how I envision the circuit to be much like a hand held DMM which may be connected to any differential voltage within its operating range without regard to DMM's input common mode voltage range .

Regards
ik

0 Guang Zhou over 6 years ago in reply to imtiaz khan

TI__Mastermind 34060 points

Hi IK,

OK, as long as you connect the battery ground to the ground of the sensed circuit, it should work. So in this sense, you’ll have a third ground connection in addition to the “two probes” in your DMM example.

Regard, Guang

0 imtiaz khan over 6 years ago in reply to Guang Zhou

Intellectual 440 points

Hi Guang

Thank you for the prompt reply.

I still however would like to understand why would I need the third ground connection? Incidentally a simulated circuit works correctly without the third ground.

Regards

0 Guang Zhou over 6 years ago in reply to imtiaz khan

TI__Mastermind 34060 points

Hi IK,

The INA240 requires dc input bias currents to work properly. The bias current is drawn from the circuit that you’re sensing and they need to return to the same circuit. This is the reason why you’ll need the ground connection. A simulation shows the “correct” waveform doesn’t mean you’ll get a correct response in real world reliably. At the very least there is going to be distortion and possibly other strange behavior.

Regard, Guang

0 imtiaz khan over 6 years ago in reply to Guang Zhou

Intellectual 440 points

Hi Guang

Thank you very much for all your detailed answers.

Regards

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INA240: INA240