INA186: Looking for solutions to detect 10uA current

Austin Do

Intellectual 2175 points

Part Number: INA186
Other Parts Discussed in Thread: INA149, AFE3010, INA229

Hello experts,

I'm looking for CS solution to detect 10uA ~20uA current.

This is not a main power rail, but 220VAC GND line. The purpose of CS is to detect leakage current.

Can you please recommend the proper solution for this application?

Best Regards,

Austin

over 2 years ago

0 Peter Iliya over 2 years ago

TI__Mastermind 29655 points

Hey Austin,

I am looking into this and will respond shortly.

Best,

Peter

+1 Peter Iliya over 2 years ago

TI__Mastermind 29655 points

Hey Austin,

Sorry for the delay. There is no easy solution. The first thing to address is the large common-mode swing. You would either need an amplifier rated to these voltages (e.g., INA149) or create a floating DC supply that moves with the line voltage and use this to power an INA186. Although you may need to protect the INA186 for when VCM goes below 0V using a clamp, thus you may need to INA186's. One to measure leakage from HOT to ground and the other for Neutral to ground. While one is measuring current, the other is essentially turned off. The INA186 can easily measure 10uA of current, but its Abs Max VCM cannot be > 42V nor < -0.3V.

The problem is that measuring leakage current is effectively measuring differential line current. Usually current transformers are used to detect ground fault current in range of 5mA (which the AFE3010 does). But I am not sure there are current transformers that can pick up on 10uA of differential current. If there are some, then maybe you could use that along with an amplifier to measure the output coil current from transformer.

Otherwise if no transformer is used then you may need to measure HOT and NEUTRAL (return) currents directly and then take the difference of them to determine what the differential current is. This will be difficult since these system can be rated to 20A, and thus you would need to have resolution of at least 10uA over the range of 20A, which is a large dynamic range. The INA229 has a large dynamic range and maybe could get you there.

Here are some relevant documents. There is not one clear solution. The last one shows how to convert a voltage-output CSA into a current-output CSA. This is helpful when needing to level shift a floating output to a ground-reference level using a transistor as shown in the circuit document preceding the last document. If you go with a digital part (INA229), then you can always level shift the SDA/SCL with digital isolators.

https://www.ti.com/lit/ug/tidua56a/tidua56a.pdf?ts=1619675574417&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FTIDA-00442

https://www.ti.com/lit/ug/tidu873a/tidu873a.pdf?ts=1634325136393&ref_url=https%253A%252F%252Fwww.google.com%252F

https://www.ti.com/lit/ug/tidu833/tidu833.pdf

https://www.ti.com/lit/an/sboa358/sboa358.pdf?ts=1619563437533&ref_url=https%253A%252F%252Fwww.google.com%252F

Sincerely,

Peter