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WEBENCH® Tools/LM3481: Simulation, hardware & system design tools forum

Ryan Hair
Prodigy 175 points

Part Number: LM3481

Tool/software: WEBENCH® Design Tools

I am trying to figure out how the current limiting function works. I am a bit confused since the Webench design is a little different from what the datasheet says. Ultimately I would like to add a trimpot for tuning the current limit if possible. Right now the input voltage is set to 3-4.2V, output voltage 5V, and output current limit to 15A.

In the datasheet, it shows a single resistor- Rsen.

In the Webench design tool, it has an additional resistor. What is Rfilt doing? Is it supposed to be forming a voltage divider? In addition, when I change my desired output current, webench adjusts the value of Rsense. If I wanted to tune the resistance of Rsense in real life, I would need a small footprint SMD power potentiometer, which does not exist. Can Rfilt be made a potentiometer instead since not much power flows across it?

  • 0
    TI__Expert 5920 points

    Hi Ryan,

    Resistor "Rfilt" used by Webench provides an additional flexibility to user to increase the slope of the compensation ramp externally as shown in image below.

    Kindly refer page 14 of datasheet for more details.

    Datasheet link: http://www.ti.com/lit/ds/symlink/lm3481.pdf

    We are looking for the right contact to address the query regarding Rfilt being made a potentiometer. We shall soon get back to you on the same.

    Thanks and Regards,

    Umayal

  • 0 in reply to Umayal Ramanathan
    TI__Guru* 79805 points

    Hi Umayal,

    Thank your for answering.

    Hi Ryan,

    Rflit and Cflit also serves as a low pass fitter to suppress the leading spike current at the current sense signal to avoid tripping the peak current limit falsely.  Without it you may see a large leading edge spike on the sense current signal.

    Hope this explains.

    Best Regards,

    Youhao Xi, Applications Engineering