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Current Shunt as a feedback for coils

Chen Song Chaw40
Prodigy 50 points
Other Parts Discussed in Thread: INA300

Hi all,

I need to had a feedback from an output source (coils).

Currently I use a opto to detect the status (voltage) for feedback.

The problem is that if the load (relay/values) not wired it will still had the signal feedback.

So I was thinking using a current shunt as the feedback signals.

Which of the current shunt IC suitable for this application?

The coils supply is 24Vdc.

Input to the signal will go to a micro. of 3.3V, a logic will work. Just need to know the status of the load.

Thinking of using the INA199A1 for this application.

Regards

ChawCS

  • 0
    TI__Expert 4595 points

    Hi Chen,

    What is the minimum and maximum current that is needed to be measured . Can you provide a schematic for this application.

  • 0 in reply to Rabab Itarsiwala
    Prodigy 50 points

    Hi,

    I am driving a SMC SY3000 values.

    The coil is 0.4W, with supply of 24Vdc. So the current about 20mA.

    I just need to had a logic feedback. That is to say, is it ON or OFF.

    Currently I had try using a opto feedback, but if the valus is not present (wired) is still had signal back to the processor.

    The processor is working on 3.3V.

    For the actual schematic, I had not design it.

    Regards

    ChawCS

  • 0 in reply to Chen Song Chaw40
    TI__Expert 4595 points
    Hi Chen,
    I am not completely familiar with your application. Are you looking to sense a maximum current of about 20mA on a 24V bus? What are your other requirements? From what I understand, INA199A1 can be one of your choice.
  • 0 in reply to Rabab Itarsiwala
    Prodigy 50 points
    Hi,
    Sorry to confuse you.

    My application is simple.
    I just need to check if my output values is active when I send a ON signal and deactive when it is OFF.
    Normally we will use a voltage signal to feedback, using opto.
    The problem is that if the values coil is open, there will still had voltage feedback.

    So I was thinking using a current source for feedback.
    As my design is using a driving source. (the coils is link to ground).
    I think is better to had low side sensing. (please advice).

    Another thing is INA199A1 can it have a 3.3V for logic 1 and 0V for logic 0.
    It will interface with the microcontroller, I dont need another lever shifter.

    Regards
    ChawCS.
  • 0 in reply to Chen Song Chaw40
    TI__Intellectual 2480 points

    Hello Chaw,
    You may be interested in the INA300.  This is a current shunt monitor used for overcurrent detection.  The threshold current for triggering is set by an external limit setting resistor, and when that threshold current is passed the device will toggle its active-low Alert pin. This device can operate off of a 3.3V rail while sensing common mode voltages of up to 36V.

    The Alert pin is open drain so you will need a pull up resistor, but that shouldn't be a concern.  You should note that the output low voltage for this device can be as high as 400mV.

    Does this device fit your application?  If not, please provide more information about the expected environment.  What will be the current on the bus when the valve is shut vs the current on the bus when the valve is open?

    Best regards,

    Kareem Moulana

  • 0 in reply to Kareem Moulana
    Prodigy 50 points
    Hi Kareem,
    I will study the INA300 too. Currently looking at INA199A1.

    Now my design for the values/coil is a driving source (the load is link to the gnd).
    This I will use the low-sensing.
    The values/coils will be ON (20mA) or OFF (0mA)

    This design may change to a sinking source (load all link to the 24Vdc)
    For this I may need to use the high-sensing.

    I will test out the INA199A1 first, as I had request the sample from TI.

    Regards,
    ChawCS
  • 0 in reply to Chen Song Chaw40
    Prodigy 50 points

    Hi all,

    Some info, to share..

    I had tested the INA199A1, is a small chips SC-70-6.

    It work as what I expected.

    I need to put a sensing resistor of 3 ohm, ref wire to GND

    So from calculation 

    Current to coil = 20mA, sensing resistor of 3 ohm, and gain of 50 (A1)

    I can get the output voltage of 3V, to the microcontroller GPIO

    BR,

    ChawCS