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TPS2663: Slow acting fuse needed

Hans van de Laar
Prodigy 130 points
Part Number: TPS2663
Other Parts Discussed in Thread: TPS1686, TPS25984B

Tool/software:

In our application we need to fuse the load at 0.9A.

However, the load is allowed to use 5.5A for 20ms. During the 20ms at 5.5A the fuse should not trip. 

How can we make the TPS2663x act more like a slow blow fuse?

Not sure, but it seems the I_lim pin output a current, relative to the output current. 

Is it allowed to place a capacitor over R_limit, so decrease the voltage rise over R_limit, during the current peak? 

Regards, Hans

  • 0
    TI__Mastermind 31241 points

    Hello Hans,

    You want to allow 5.5A current for 20msec with our tripping the fuse, right!

    Please let me know your operating voltage and application for this requirement.

    Thanks

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 130 points

    5.5A for 20ms, without tripping the fuse.

    Working voltage is 12V

    UL rating of the part  would be preferred.

  • 0 in reply to Hans van de Laar
    TI__Mastermind 31241 points

    Hello Hans,

    With TPS2663 we don't have this blanking feature.

    TPS1686 which will be released this year September has iTIMER feature which is 80V and 10A part.

    You can also check TPS25984B, 16V part with iTimer feature.

    Let me know if you need further information on this.

    Thanks 

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 130 points

    Hi Amrit, 
    Thanks for the suggestions. I will look into this. 


    But related to the original question:
    Can a capacitor over the Rlimit delay the tripping?
    Is the current sourced on ILIM a ratio of the output current? What is this ratio? 

    Regards, Hans

  • 0 in reply to Hans van de Laar
    TI__Mastermind 31241 points

    Hello Hans,

    Sorry for the delay in response.

    Cap on ILIM can't introduce delay. RILIM puts threshold voltage for the comparator to select the IOL.

    Cap on ILIM can lead to a difference in threshold which could trip the IC at lower current.

    Thanks 

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 130 points

    Hi Amrit, 

    Can you give me a bit more detail why not?
    If I_lim output a current, proportional to the output current, and a resistor will set the trip voltage, a capacitor in parallel with the resistor will add a delay in voltage rise. If the capacitor is ideal and have no leakage current, the same end voltage will be reached, but later in time.  

    is I_out not an current source?

  • 0 in reply to Hans van de Laar
    Prodigy 130 points

    Hi Amrit, 


    We did some measurements.
    It seems that:
    * The Ilimt pin source current is proportional to the device output current: about 27.8uA/A.
    * The internal comparator triplevel would then be 500mV
    Can you confirm this?

    R_lim is now set to 20k, which set the I out limit to 0.9A. Simulation shows, when placing a 10uF capacitor over R_lim, it take about 35ms before the 500mV trip level is reached with a 5.5A, 20ms peak. 

    Any other thoughts? (I see in the datasheet that there is a whole block making use of the I_lim voltage--> Gate control logic; Power limit Amp; current limit amp; fast trip comp; open/short detect)

  • 0 in reply to Hans van de Laar
    TI__Mastermind 31241 points

    Hello Hans,

    Thanks for the measurements.

    I have to run some simulations and experiments to confirm this.

    I will update you by early next week.

    Thanks 

    Amrit 

  • 0 in reply to Amrit Jit
    TI__Mastermind 31241 points

    Hello Hans,

    We have run some simulation by keeping cap in RILIM. Even though there is delay before ILIM activation but below are some problems which could come because of the circuit.

    1. Inrush current limiting will be slow, and device could burn during starting.

    2. Because of cap, pole is introduced on control circuit of ILIM which could compromise loop stability.

    3. Ringing on ILIM pin which could lead to unwanted shut down.

    eFuse with iTIMER will serve the purpose. Please check the suggested parts as mentioned on above threads.

    Thanks 

    Amrit