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Original question:

TPS2492: High Powered - Brushed DC Motor Application - Overheated FET Damage / Burnt

TPS2492: Do I need HotSwap for Pluggable Machine consist of DC Converters?

Calvin Tanudjaja
Prodigy 35 points
Part Number: TPS2492


I am pretty new with Hot Pluggable Machine.

My current project is to create design that can plug and unplug the system at runtime.

The Machine consists of:

  1. DC Converter 1000 Watt with 800 uF capacitance
  2. DC Converter 200 Watt with 1300 uF capacitance
  3. DC Converter 50 Watt with 300 uF capacitance

3 of the DC Converter will have inrush current because of the capacitor inside, the activation time for 3 of them is quite different

  1. after 50 ms receiving 48V, there is inrush current around 33A
  2. immediately after receiving 48V, there is inrush current around 25A
  3. Nothing can be observed for the small DC Converter

My DC converters does not have "Enable" for TPS2492 PG function

My question is, Do I really need TPS2492 in the first place? since the DC converter will only turn on, and the load on the output side of DC converter will not be turned on directly until signal being given to them.

If I do not really need HotSwap Board, what other consideration do I need to take for this connection between the Power Supply (From Battery) to this machine?

I tried to use the calculator with my selection of FET but it seems that my FET spoilt after my first activation

 Hotplug Calculation.xlsx

Thank you!

  • 0
    TI__Guru** 107121 points

    Hi Calvin,

    Thanks for reaching out.

    Does your DC converter has soft start circuit ? What is the turn on threshold of DC converters ? Can you please share the block diagram including capacitances in the path.

    Best regards,

    Rakesh 

  • 0 in reply to Rakesh
    Prodigy 35 points

    Hello,

    As far as I know there is no softstart on the DC converter

    You can see the combined system inrush current here


    Only the 1000W Converter (33A)



    Only the 200W Converter (25A)

    Only the 50W Converter (negligible)

    All Yellow Line above is V supply to the system direct 52V (Battery with Nominal 48V)

    Threshold will be according to the datasheet of 48V
    which technically 19V for the 1000 watt

    SD-1000-SPEC.PDF

    and 36V for 200 and 50 Watt, although not tested yet

    SD-50-SPEC.PDF

    There is no other capacitance along the Vout, after the HotSwap board it will be one small capacitor according to HotSwap design and all the loads (there will be additional loads which are another 2 Boards which has more 2000 uF each.
    Seems all my load has high capacitance value.

    Thank you!

  • 0 in reply to Calvin Tanudjaja
    TI__Guru** 107121 points

    Hi Calvin,

    Thanks for the details.

    If the load turn-on threshold is 19V, then we should enter that value in cell F68 in the design tool. It is very challenging to startup smoothly with such very load. Please find a way to control DC converter module and enable them using PGOOD of hot-swap.

    Best regards,

    Rakesh 

  • 0 in reply to Rakesh
    Prodigy 35 points

    Hello Rakesh,

    Because the load on the output side has a different Startup Voltage value, what should I put there? is it the lowest one from the system?
    And one more thing is the startup current, What should I put inside Startup Current? Because what I can see is Inrush Current and actually after that, there will be no current (or very small) because the load is only the converter itself, at most maybe it will only take 1-2A

    Thank you!

  • 0 in reply to Rakesh
    Prodigy 35 points

    Any Other recommendation from TI chip that can handle this without power good?
    Thank you!
    Will a normal softstart circuit sufficient?

  • 0 in reply to Calvin Tanudjaja
    TI__Guru** 107121 points

    Hi,

    Please use the lowest voltage one from the system. 

    For the Startup Current you can do as follows.

    • Calculate the power on DC converter output (Pout)
    • Startup Current = (Pout) / lowest voltage

    We don't have another solution which can start heavy load with out power good.

    Best Regards,

    Rakesh