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LM25118: Current Consumption and heating issue at no load

Jake Jung
Expert 1915 points
Other Parts Discussed in Thread: LM25118

Hi.

My customer has designed using LM25118 and testing the board.

At no load, the board's current consumption is 40mA, and LM25118 is a little hot.

This current consumption is normal? 

Please check attached schematic and please let me know no load current consumption and how to reduce it.

Thanks.

  • 0
    TI__Mastermind 21720 points
    SS Jung,

    What is the input votlage? If it is high the internal LDO for the VCC rail will dissipate some power. Also can you provide a schematic that is more readable? It's hard to tell how everything is connected due to there being no dots where lines are connected.

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Expert 1915 points

    Thanks.

    I attached clear sch image.

    Input  (OPT_VCC_SYSTEM) : 19V ~ 30V

    Output (OPT_+24V)  : 24Vdc / 3Adc

    SCH1.pdf

  • 0 in reply to Jake Jung
    TI__Mastermind 21720 points
    SS,

    When you say the board is pulling 40mA are you talking about the VIN pin of the LM25118 or the node labeled OPT_VCC_System? If you are measuring at the latter please remember the the UVLO resistor divider and FB resistor divider will consume some current.

    Also what is the temperature of the LM25118 that you are measuring?

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Expert 1915 points
    Yes. VIN is OPT_VCC_SYSTEM and this is 19V~28V.
    When output is no load, current consumption is about 40mA on VIN side.
    UVLO and FB divider resistors are recommended value in datasheet and Webench.

    I don't know exactly temperature but when chip is touched by finger, it feels hot. Because 28V x 40mA = 1.12W.
    As I know when VCCX=0, VIN Operating Current is 4.5mA in datasheet 7page, Electrical Characteristics.

    This 40mA at no load is normal current? Because UVLO and FB Resistors?

    Please help me.
    Thanks.
  • 0 in reply to Jake Jung
    TI__Mastermind 21720 points
    SS,

    The IC will typically pull 4.5mA when the device is operating with no external VCC, as you mention. Internally the LDO is what is going to dissipate the most power and at no load this will be very small. Please insure that you are just measuring the current on the VIN pin.

    Thanks,

    Garrett