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LPV821: High Side Current Sensing Using LPV821

Hari T O0
Genius 3820 points
Part Number: LPV821

Hi,

I am making a high side current sense using LPV821 and Si7948(PMOS from Vishay).

During simulation(Transient analysis) I can see a peak initially. Please see the attached image. May I know is this due to the fault in my circuit or the

way I am doing simulation in TINA is wrong(I am new to Tina). May I know how to sweep the current source from

.2mA to 100mA with a step of 0.005mA.

Regards

Hari

LPV821_CS - autosave 18-08-16 12_42.TSCI am also attaching the simulation file along with this.

  • 0
    Guru 140200 points

    Hi Hari,

    can you please explain in detail what the purpose of this circuit is? What do you need U2 for?

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 24560 points

    Hari

    Kai's question is very valid because the technique you are showing where you drive the MOSFET with it part of the feedback loop of the amplifier is used when the the supply you are monitoring is outside the operating range of the amplifier.  In this application where the voltage source is within the operating range of the LPV821, a simple difference amplifier configuration would work.  I would also like to note that your simulation has the supply voltage of the LPV821 set to 5V and this is a 3.6V max device.  The simulation is allowing this but this should not be implemented this way.

    To answer your question about why you are seeing the peaking is most likely the turning on of the VS1 source.  If you run your simulation where the steady state condition of the system is calculated before the transient is run, you will not see that spike.  Choose the option to "calculate operating point" and then run the simulation.  Allowing some circuit settling time is always recommended, so the ADC that is analyzing VOUT would not capture this spike.

    In regards to sweeping, this function is not well documented in TINA but it is possible.  First, in the Analysis tab, choose Mode.  Change current mode from "single" to "parameter stepping".  After hitting OK, go back into the Analysis tab and choose "Select Control Object".  An arrow should pop up and select the Isense which is what you want to step in your analysis.  Once the box opens, click on the ... next to your 10m value and you can now choose the sweeping range and number of steps.  When you now run your transient analysis, it will be run once per step and the results will all be superimposed on the screen.

    Chuck

  • 0 in reply to Chuck Sins
    Genius 3820 points

    Hi Chuck,

    I changed the simulation settings and run it again.I am not getting the o/p without spike.

    Please see the image attached which shows my simulation settings and o/p wave form.

    May I know what is the difference between current source and current generator in TINA TI

    Regards

    hari

  • 0 in reply to Hari T O0
    TI__Mastermind 24560 points

    Hari

    The image you are showing actually does not have the spike (overshoot) of your previous simulation.  If you look at the y-axis values, this plot is very zoomed in on the y-axis scale. What you are seeing is essentially noise and these fluctuations are extremely small.

    In regards to your question about current sense source and current generator, the current source is a fixed DC current. The current generator option provides several options to create a specific current waveform.  You will see these options when you double click on the current generator you insert in your schematic.  The options are selected by clicking on the line labeled "signal'.  The default source is a "unit step" but that can be changed.

    Chuck

  • 0 in reply to Chuck Sins
    Genius 3820 points
    Hi Chuck,

    Thank you very much.I changed the Y axis accordingly .Now it is working fine.
    May I know does TI have any materials which describes how to use "T&M" tools in TINA TI,that is Multimeter,Oscilloscope etc

    Regards
    Hari
  • 0 in reply to Hari T O0
    TI__Mastermind 24560 points

    Sorry Hari

    I’m not personally familiar with those features. I’ll see if I can forward your question to the WEBENCH forum but you may get faster response posting that question on the WEBENCH forum yourself.  

    Chuck