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TPS61085: adding current limit resistor at output

Shamir aharon
Prodigy 20 points
Part Number: TPS61085

Hi,
I have a working boost converter based on the TPS61085 chip, 
I want to make some changes so the design will get certified as IS (Intrinsically Safe).

The most important change is limiting the current at the output, and I plan to do that with a resistor (as small as possible) in series with the load, (see picture attached)
the output voltage is set to 12V, and the max current that I will drow is 0.3A,

As the current flow on this resistor, there will be a power drop on it, and the load will get less voltage than I needed, 
to overcome this, I wanted to connect the feedback pin after this resistor,


Will this work? 
How will the system react to high current changes?
Any other good idea to make the system IS approved?

Thanks
Shamir

  • 0
    TI__Genius 14585 points

    Hi Shamir,

    It is not recommended to add resistor to the switching loop (low side mos, diode, output capacitor).

    The switching loop is critical and adding resistor(inductor)will cause higher spike and bad performance.

    The resistor could be added between the two capacitors.

    it will be safer to keep one capacitor close to minimize the switching loop.

    Also, it shall be better to detect continuous current on the resistor.

    The feedback circuit could be connected to anywhere that you wish to be regulated, like top of C385.

    Best Regards

    Fergus

  • 0 in reply to Fergus He
    Prodigy 20 points

    Thanks for the quick response, 
    so is this design what you recommend?

    also, what do you mean by "it shall be better to detect continuous current on the resistor." ?

    Thanks

  • +1 in reply to Shamir aharon
    TI__Genius 14585 points

    Hi Shamir,

    The schematic is just what I mean.

    Shamir aharon said:
    "it shall be better to detect continuous current on the resistor."

    When detecting the current of diode, it is a discontinuous triangle wave that may hard to measure the average value and need to be filtered.

    When detecting the current behind the capacitor, it would be a continuous current with small ripple and will be easy to use.

    Best Regards

    Fergus