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LM5119Q: LM5119Q not providing the required load current

Karthik M1
Prodigy 70 points
Part Number: LM5119Q

Hi,

I've designed a PCB using LM5119Q.  The circuit is designed to generate 27V, 1.6A and 38V, 4.3A. The circuit is operating properly under no load conditions. If the load is connected after the required voltages generated, the circuit is able to source the required amount of current. But if the circuit is switched on with the load connected beforehand, the circuit is not able to source the required amount of current and the output voltages do not reach the required levels. Please find attached the schematic for your reference.

Please help me with this.

Thanks and Regards,

Karthik

LM5119Q.pdf

  • 0
    TI__Mastermind 24075 points

    HI Karthik, 

    You can check if the system is stable at load condition?

    Also, if the load is connected before startup, can you use current probe to check if there is surge current caused by electronic load?

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 70 points

    Hi Qian,

    Thank you for your quick response.  Could you please elaborate on the RES pin of LM5119Q ?. Because, connecting RES to any of the VCC pins seems to solve the issue. Will the system be stable in this state?

    Regards,

    Karthik

  • 0 in reply to Karthik M1
    TI__Mastermind 24075 points

    Hi Karthik, 

    The RES pin is to set the off time when OC happens and the part enters hiccup mode. 

    By connecting RES pin to VCC, the off time is minimized. The part will restart immediately over and over. It is kind the hiccup mode is disabled. 

    This method is not recommended, because if OC or short circuit happens during normal operation, the power loss on FET and inductor will be very high and damage may happen. 

    I still suspect the original issue is related to E-load, but needs to be confirmed on your side. 

    Thanks

    Qian