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LM5122: LM5122MH/NOPB

Sivakumar Kancharla
Prodigy 50 points
Part Number: LM5122

Tool/software:

i designed a booster using webench tool,  that specifications input voltage is 5V and output is 50V and 4A maximum.

below i attached  schematic and bom of the booster and once please review it and let me know weather its working or any changes required for my specifications?

Booster circuit.pdfBOM 08_08_2024.xlsx

and here inductor value and mosfet part numbers are not given please suggest any parts also

Thanks&regards,
K Sivakumar.

  • 0
    TI__Mastermind 30250 points

    Hi Sivakumar,

    Thanks for using the e2e forum.
    Is the 5V input voltage constant, or is there a range for the input voltage?
    I will review the design and get back to you on Monday.

    Thanks and best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 50 points

    I will give 5V but whenever load is connected that time voltage will be down from 5 to 3V

  • +1 in reply to Sivakumar Kancharla
    TI__Mastermind 30250 points

    Hi Sivakumar,

    Thanks for the confirmation.

    Here are my comments on the schematic:
    - BST cap (C7) is 47uF. This value is very high. I would expect a value like 470nF instead.
    - The UVLO voltage divider is set to trigger undervoltage lockout at 4V, so if the input voltage would fall down to 3V, the device would go into shutdown.
    It is important to start up with 4.5V input voltage or higher, which is required for initialization of the device. Afterwards Vin can go down to 3V.

    - Inductor, compensation and output caps all look good to me.

    - Regarding the MOSFET choice, I am not a full expert on FETs, so I cannot give a recommendation here.
    You can check reference design for LM5122 to see which FET parts are used here. (e.g. LM5122EVM : https://www.ti.com/tool/LM5122EVM-1PH )
    If VIN is 5V, the VCC voltage and therefore the gate driver voltage will be 5V as well. When operating with low input voltage, it is recommended to choose logic level FETs, which have a lower turn-on threshold to make sure the FET can fully turn on.

    Best regards,
    Niklas