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# INA169: Circuit review - filtering doubt

Part Number: INA169
Other Parts Discussed in Thread: INA296A, INA296B

Hello team TI,

I'm starting a project for a current monitor, with the following characteristics:

- voltage in the range of 30VDC to 70VDC

- maximum current of up to 400A (Imax)

- minimum current 0A (no negative current)

- shunt to use is 0.1875mOhm and the differential voltage of the shunt at 400A is 75mV

- desirable error < 2% in the range of 20A to 120A

- the analog output must be a maximum of 3.3V for input into the microprocessor AD converter

After reading the documentation and respective datasheet, it seemed to me that the best option is INA169. I deduce from what I read that this would be the most suitable circuit, basically what appears in the datasheet:

- can the circuit be considered stable, in the sense of its use under the above conditions?

- would it be necessary to use filtering in this circuit?

- where would CL be used, if necessary, in the above circuit? What is the CL value? (I couldn't understand the exact purpose of filtering calculation, please, I need help on this matter)

Thank you very much for any help!

Best Regards, Luiz

• Hello Appreciated Engineer,

I am looking this over and will respond shortly.

Best,

Peter

• Hey Luiz,

Filtering is only necessary if there is significant current noise and/or you can reduce signal BW according to the resulting differential cutoff filter frequency, Input capacitors for this device will not serve any other purpose. The circuit will be stable as it is.

As a note about accuracy. The INA169 does have a max rated ±1mV offset so it does not seem possible you will achieve <2% error at 20A (3.75mV Vshunt). 1mV/3.75mV = 26.7%.

In order to achieve this accuracy you may need to consider using this circuit below where you can take a more accurate voltage-output device (e.g., INA296B or INA296A) and use this architecture to make it an output current circuit.

https://www.ti.com.cn/cn/lit/an/sboa513/sboa513.pdf

https://www.ti.com/lit/an/sboa358/sboa358.pdf

Sincerely,
Peter

• Hi Peter,

Thank you very much for the quick response, very accurate. I see that the amplifier I was thinking of for this project could not be used. I'm going to study the datasheet of the amplifier that was suggested (INA296x) and try to redo the circuit, although it seems a little more complicated to me. I will send you a private message about this ongoing project to allow a broader view of what I intend. Perhaps I will have even more effective help from you.

Once again, thank you very much for your response and help!

Best wishes,

Luiz