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INA180: Feasibility of using INA180A1 for "OVER CURRENT SENSING APPLICATION WITHIN 2uS " for MOSFET based 3 phase inverter

Part Number: INA180
Other Parts Discussed in Thread: TL331, , INA303

Hello,

I am designing a MOSFET based 3phase inverter and need a OPAMP for SHUNT based over current detection on DC NEG side  and  i am planning to use INA180A1 with a GAIN of 20  followed by TL331 comparator for overcurrent protection.Comparator reference is set at 2.5V.

1) Will it detect OVER CURRENT within 2uS.

2) Is the slew rate and bandwidth sufficient enough for OC protection functionality.

  • Hello Bharath,

    Thanks for considering to use Texas Instruments.  Based on the details you provided, I presume with respect to the forward current direction your IN- pin is on the high side or your shunt and IN+ is on the low-side of your shunt.  I also presume you have the INA180 output fed directly to the IN+ pin of your TL331 and 2.5V reference feeding into the TL331's IN- pin.

    1.  Assuming your OC event rails the INA180s, the INA180 output at best will take 2.5V/(2V/us)=1.25us to create an output the will trigger the TL331.  This time also is only valid if there is only parasitic resistances and capacitances between the devices that are negligible enough to be neglected.  As for the TL331, its a little less clear and I will need to verify with someone from that product line. The datasheet claims you should be able to calculate the response time according to the pull up resistor and load cap, yet the typical value in the table deviates from my calculation.  I would calculate the response time to be -RC*ln(1.4V/5V)=-(5.1E3)*(15E-12)*ln(1.4/5)=97.4ns.  The table says 0.3us, which might actually correspond to a 3 sigma max rather than a typical (will need to check with product line representative, my products are current shunt monitors).  In the interim, to get an estimate I would use -3*(Your Pull-up)*(10pF pin cap + any additional cap on output)*ln(Your required voltage/pull up voltage).

    2.  It depends.  I would recommend building your OC circuit in TINA or some other SPICE program and testing it.  Also once you do that you can provide us with pictures of what your OC condition might look like, which will help determine if it can be used for you or not.

  • Thank you for your reply i will be back with my model and simulation

  • Hi Bharath,

    Have you checked out the INA303 with built in H/L over current detection comparators? 

    /cfs-file/__key/communityserver-discussions-components-files/14/TI_2D00_INA303.pdf

  • Hello BP101,

    Product is a cost sensitive one cannot efford INA303. 

  • Hello Bharath,

    I reached out to the comparators team on the TL331. From that the response time of the TL331 could be decomposed into an internal propagation delay and external RC rise time. For the propagation delay, this relates to the overdrive voltage. Newer comparator datasheets typically have a graph for this. It should have an exponential decay characteristic like the example graph shown below. Based off figure 5, we can construct our own. By generating your own, you can leverage excel to generate an equation to exponentially fit the line. Or you can manually derive coefficients. If you prefer to derive, this site explains how you would do it. Based off that, I derived my own coefficients found in the attached excel document. With those coefficients you can then estimate what the propagation delay might be for a small overdrive voltage (<100mV). Above 100mV overdrive, you could assume the 100mV propagation delay time and add the RC charge duration to determine the response time.  In the excel document, y corresponds to the propagation delay in microseconds while x corresponds to overdrive in mV.

    /cfs-file/__key/communityserver-discussions-components-files/14/TL331.xlsx

    As for charging up the output capacitance to a certain value, you could use the equation V(t)=Vo(1-exp(-t/RC)).   Based on figure 5, I think their probe capacitance might be a typo as Vo should be closer to 1.622V after ~10us if CL=50pF. 5pF would yield a curve closer to what is displayed. As such, I am forwarding this thread to their team for them to comment on.

    So for now, I think you could estimate your response time by summing the following: (INA180 slew duration) + (INA180 output capacitance charge to 2.5V duration) + (TL331 propagation delay) + (TL331 output capacitance charge to desired output voltage duration)