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Original question:

INA241A: INA240 BCI Test Problem

INA241A: Proper EMS protection

Tomasz Jastrzebski
Prodigy 202 points
Part Number: INA241A

Tool/software:

Hi TI,

I have to make sure that the circuit I design is properly protected against external electromagnetic field to meet EC standards.
Proper protection is particular important since wires to current sensing shunt can quite long, I would say up to 20m.
I would also like to achieve at least some overvoltage protection in case circuit is connected incorrectly.
Below is what I came up with. Does this diagram make sense? Can it be simplified?
TVS diodes are 600W peek power min.
Please advise.

Kind regards,
Thomas

  • 0
    TI__Mastermind 29710 points

    Hello Thomas,

    What is it you are injecting, current or voltage.  Will long cables I am assuming something like a BCI test?  I am slightly familiar with this test but I assume in that case the cables would have current injected.  I will speak with someone that has some experience with this.  Just to place my thoughts is the ferrite beads will be large impedance at high frequency have you simulated at expected current injections to verify no issues?  

  • 0 in reply to Javier Contreras4
    Prodigy 202 points

    Hello Javier,

    BCI test is one common and probably the main scenario that should be considered but it would also be nice if the circuit was reasonable immune to human mistakes like connecting lead wires not where they are supposed to be connected. In such case differential voltage can easily exceed 24V, although it should stay below 30V (INA241 max differential voltage).

  • +1 in reply to Tomasz Jastrzebski
    TI__Mastermind 29710 points

    Hello Tomasz,

    The only concern is the speed of the currents and magnitude going through the ferrite beads.  The other issue I see is the negative VCM.  Going below -20V will be an issue.  I have not used TVS diodes but I assume the break down of D4 is 10.1 and D2 and D3 will be forward biased leaving the negative common mode limited to about 10.1V +0.7V below GND.  The top side of VCM limited to 70.1 +0.7.  

    If this is the case I think you will be fine except my initial concern about ferrite beads and limiting the high speed currents.  You may have more experience on this.

  • 0 in reply to Javier Contreras4
    Prodigy 202 points

    Hello Javier, thank you.