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LM5156: Differential OpAmp for Current Sense

Nassim Mediouni
Prodigy 30 points
Part Number: LM5156

Hello,

can I use a differential OpAmp to monitor the voltage of my shunt resistor and provide the output to the CS pin?

My application requires a very low resistor (about 2mOhms) and I want to seperate the power Gnd of the shunt from the Gnd of the LM5156 to avoid Gnd noise.

What would happen if I use the slope compensation function with the Rsl resistor knowing that it is the output of the differential amplifier which is connected to the CS pin?


Thank you in advance.
  • 0
    TI__Genius 10385 points

    Hi Nassim,

    Thank you for using E2E forums, in our datasheet it states that the shunt can be connected to the power ground and there is also a filter that is usually recommended, and why do you need to use a op amp to give output to the CS pin?

    BR,

    Haroon

  • 0 in reply to Haroon Wardak
    Prodigy 30 points

    Hi Haroon,

    thank you for your feedback.

    The recommended filter allows to avoid the noise generated at switch ON of the Mosfet but it can't avoid ground shift between the power Gnd and the IC Gnd. I have a very high peak current (about 50A) so I will need a very low value for my shunt resistor (less than 2 mOhms).

    Si I use a differential measurement to cancel the ground shift between the power part and the IC part.

    Best regards, Nassim.

  • 0 in reply to Nassim Mediouni
    TI__Genius 10385 points

    Hi Nassim,

    I see, well we have not recommended this setup in our datasheet so I would not be able to answer what will happen if you did what you are describing. However, I do not think having Rsense smaller than 2m ohms for peak current of 50A is a problem, normally you can have two parallel sense resistor to even achieve smaller Rsense.

    In any case, no the RC filter I mentioned is to remove the noise from the CS signal as you can see in the datasheet page 22.

    BR,

    Haroon

  • 0 in reply to Haroon Wardak
    TI__Genius 10385 points

    Hi Nassim,

    I will close this thread. If you have further questions just reply on this thread.

    BR,

    Haroon