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TPS25980: unavoidable thermal shutdown during startup with high capacitive load

Christopher Pelczar
Prodigy 10 points
Part Number: TPS25980
Other Parts Discussed in Thread: TPS25940

Hello, I'd like to use the TPS259807 E-fuse to switch on the power to a board which required 24V and has 4.5mF of capacitance. For this board, I want to limit the current to 5A. Using the excel calculator for this e-fuse, I couldn't find any configuration for glitch-free startup. Is there any configuration of this e-fuse or an alternative part which can be used to switch on this highly capacitive load? Otherwise, can I allow for "non glitch-free" operation during startup having the e-fuse going into thermal shutdown intermittently while charging the capacitor?

  • 0
    TI__Guru* 79181 points

    Hi Christopher,

    Welcome to E2E. I understand you concern. 

    1. How much charge time do you want ? You can choose large dvdt cap but then charge time will be in seconds.

    2. Also you can start device in current limit. What you can do is set current limit to lowest during startup and make dvdt=open. This make device turn on in current limit and you will see thermal shutdown happening but also charging will happen if you set device for auto retry response. But we cannot calculate charge time here. After startup you can change current limit back to steady state value of 5A. You can try this on our EVM.

    This is example image for TPS25940 efuse:

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 10 points

    1. I think the board that I want to connect to the Efuse should be able to deal with a low slew rate of the voltage, so charge time in seconds should be okay. Still, according to the excel design calculator, as I increase the dvdt capacitor size, the power dissipation during startup decreases, but so does the Max power dissipation allowed for glitch-free startup for the programmed startup time (20% margin). So no matter how large I make the dvdt capacitor, I never reach the point for glitch-free startup.

    2. I can use auto retry response. How can I switch between I_lim during startup and steady state?

  • +1 in reply to Christopher Pelczar
    TI__Guru* 79181 points

    Hi Christopher,

    1. It is happening because Rlstart field will be at low value. Make it to high value in megaohms. Please try testing with cdvdt cap greater than 2.5uf.

    2. This is the way you can change current limit.

     

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    TI__Guru* 79181 points

    Hi Christopher,

    Closing thread now. Let me know if other concern.

    Regards

    Kunal Goel