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INA240: INA240

Part Number: INA240

Hello,

In my application I am trying to develop a protection circuit for a 500W-1Kw inverter using GAN. The GAN is being operated at extremely fast slew rate. I have incoorporated current sense resistor in the source path and using ina240-20v/v ic to sense the current for overcurrent.

I am not an experienced analog designer and would be indebted if any analog designer  has a look at my current protection schematic and tell me about any faults.

  • Hi Debanjan,

    Thanks for the schematic to your inverter protection circuit. Upon review there are concerns and considerations I have.

    Upon startup, false triggers can be caused by C91 and C92 charging up since they are large values. The datasheet recommends 1uF to 50uF but the lower values will have short settling times. The input circuit of R76, R80, C86, C88, C90, ZD12, and ZD13 is not required and may cause stability issues, especially if this circuit is implemented inline with the load as opposed to on the high side (floating between the positive supply rail and load) or low side (floating between ground and the inverter system).

    The polarity of C89 should be flipped with the positive terminal away from GND.

    Connections to the potentiometer should be the same (INA- and INB+ connected to middle of pot; GND on bottom pin) if you are implementing an adjustable window comparator.

    Software should consider the startup of this circuit to avoid glitches, but this entire circuit can be implemented cleanly and possibly at a lower price if you use the INA303. It is a current sensor, voltage reference, and dual comparator in one package. Please refer to the product page and datasheet below:

    http://www.ti.com/product/ina303

    www.ti.com/lit/ds/symlink/ina303.pdf

    I hope to have been helpful, Debanjan. Let me know if this resolves your concerns by replying with additional questions, or if you would like advice with implementing the INA303 to your system.

    Have a good weekend,

    Manuel Chavez

  • In reply to Manuel Chavez:

     Thank you Manuel.

    My application is low side sensing. I am using bidirectional current sensing, hence the comparator should have two references.

    I am using R76, R80, C86, C88, C90 for differential mode and common mode filtering. The problem is that my device ( GS66508B) switches at very fast rate and has rise time of 10 ns for the current when turned on. The current sense resistor has been placed in low side and has an inductance of 2-4nH. Now when current becomes Ifullload=50A from 0 amperes at switch turn-on,  there will be VL=Ldi/dt across the sense resistor that will be of very high value ( 10V) and very high frequency. The purpose of the differential mode filter is to filter it so that it wont trigger the protection circuit. D you have any suggestion for that?

  • In reply to Debanjan chatterjee:

    This is my sense resistor configuration, the previous result was that of oscillations at zero crossing

  • In reply to Debanjan chatterjee:

    Debanjan,

    How long do these false triggers last? It is understood that current only goes from 0A to 50A at startup, but this may not be the case. To help reduce the surge current through Rsense, the capacitance of C88 can be increased to 1uF or 10uF.

     

    If this trigger is false every time the GaN device switches, TI’s INA302 and INA303 have a delay feature for one of the two in-package comparators to have up to a 10u second delay before triggering the alarm output (page 15 of datasheet: http://www.ti.com/lit/ds/symlink/ina302.pdf). With one of those parts, your circuit could be simplified similarly to the diagram below (page 17, datasheet):

     

     

    Could you include what each curve on the oscilloscope screenshot represents and the value of Rsense? If it is oscillating, the circuit is likely unstable.

     

    Thanks for your patience,

    Manuel Chavez

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