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  • TI Thinks Resolved

LM25119: the circuit cannot enter hiccup mode during output short circuit fault condition

Part Number: LM25119

Hi,

My customer reported, their LM25119 design can properly enter hiccup mode in overload protection, while cannot in short circuit test. I think it is the result of current sensing mechanism of this device, correct? How can i solve this issue? (Though short circuit fault does not result damage to ckt, while the power consumption is too high if it does not enter hiccup mode.)

Thank you,

John

  • Hi John,

    I just checked on EVM, the part will enter hiccup mode with output shorted by wire.

    How did customer do short circuit test, using Eload or hard short output by wire?
    Also, can you ask customer to check if VIN is stable during short circuit test?

    Thanks
    Qian
  • In reply to Qian Chen:

    Hi,

    Thank you for reply.

    I think it related to the input voltage and inductance. Customer's design is 24V input, 5VOUT, 3uH inductance. You can try this configuration. Customer do short ckt test with wire short. Have confirmed the VIN is stable during short circuit test.

    Thank you,

    John

  • In reply to Qian Chen:

     Hi,

    I think maybe this is the inherent feature of the device.

    The condition for device to enter hiccup mode is "...detects 256 consecutive cycles of current limiting". Once the output is shorted to GND, there will be excess recirculating current in inductor, this will result the sample-and-hold DC level exceeds the internal current limiting threshold and succeeding cycles are skipped, failed to meet " 256 consecutive cycles of current limiting". Such the device cannot enter hiccup mode, instead it entering pulse skipping mode. This is exactly what customer observed. Please confirm if this is the root cause? And if so, how should we solve this problem?

    Also attached is customer's schematic. 

    Thank you,

    John

  • In reply to John11513:

    Hi John,

    The theory that the part can not enter hiccup due to pulse skip is possible.

    Can you provide the schematic with component value, so I can get more design information like Fsw, current sense circuit value and etc?

    Can you try higher output inductance and check if it helps part enter the hiccup?

    Thanks

    Qian

  • In reply to Qian Chen:

     Hi Qian,

    Here is the new one with component value:

  • In reply to John11513:

    Hi John,

    Can you increase R237, R238, R256, R257 value to 20 ohm or larger and check if it helps? Also, please check if C161 and C179 are close to CS/CSG pins in layout.

    What's the load current per phase? Please try larger output inductance. If new inductor DCR increases, the sensing resistor value needs to be adjusted accordingly.

    Thanks

    Qian

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