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INA138- High Side Current Measurement

Santhakumar S
Prodigy 150 points
Other Parts Discussed in Thread: INA138

Hi,

I have selected INA138 high side current monitoring IC from TI.

I have attached the typical scheme for current monitoring planning to implement.

1) I need to monitor the current flowing in -8000V line which is w.r.t GND. The peak current is 270mA for 20% duty.

2) One more IC will be used for monitoring the current in 100V line whicj is w.r.t -8000V. The peak current is 20mA for 20% duty.

Also i will be generating one +5V supply w.r.t -8000V and this supply will be used for IC functionality.

Whether the above said will work. If not, suggest some monitoring scheme.

Regards,

Santhakumar.S

  • 0
    TI__Mastermind 24371 points

    none of them will work, since the device is 60V rated, meaning the maximum difference in voltage among pin 5 and pin 2 can't go over 60V...

    you should scale down the level of signals with a precise divider (I would do in this way, even if you will lose in accuracy)

    Vincenzo

  • 0 in reply to Vincenzo Pizzolante
    Prodigy 150 points

    Hi Mr.Vincenzo,

    Thanks for your reply. there is a correction in the figure which i attached.

    From the figure,  you may have understood that the voltage across pin pin 5 and pin 2 is 7995V.

    Actually, it is not so.

    The voltage across pin 5 and pin 2 is 5V only.

    5V supply is generated is w.r.t -8000V. i.e., pin 5 is -7995V potential w.r.t GND. So difference will be 5V

    Input 100V is also w.r.t -8000V. i.e., the input is at -7900V potential w.r.t GND

    But I understood from data sheet that the common mode voltage between any pin and pin 2 should not exceed 60V.

    So obviously the configuration in figure 2 is not possible. What about figure 1 configuration.

    Kindly clarify the same.

    Regards,

    Santhakumar.S

  • 0 in reply to Santhakumar S
    TI__Mastermind 24371 points

    yes, the 1st is then ok, while no hope for the 2nd one...

    please note that even if the 1st is ok, you are using it to sense the current on the low-side (the lower potential) and not on the high-side (because the high voltage gap): I guess there are better devices, or at least you can use any other current sense amplifier...

    Vincenzo 

  • 0 in reply to Vincenzo Pizzolante
    Prodigy 150 points

    Thanks.

    Can you suggest a suitable method of sensing current in negative supply.

    Regards,

    Santhakumar.S

  • 0 in reply to Santhakumar S
    TI__Mastermind 24371 points

    the method is ok,

    and you can use INA138 as well. Since you are sensing on the low-side, you don't need actually a high commond mode instrumental / current sense amplifier, but you can use any precision amplifier (more p/ns available).

    for the 2nd circuit you can use the same method for the 1st: if this can't be applied then you have to look for a higher rating amplifier.

    Vincenzo