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Tool/software: WEBENCH® Design Tools


I am a beginner in power management design. I have a requirement of DC 5V, 5A power supply with the input of 24V DC. I have been through WEBENCH tool and found IC LM2678 suitable for the purpose. I carried out steady state and transient simulations and its response was fine with the values already calculated in the WEBENCH tool.

I just need to know whether I have to consider any other parameters while designing the PCB for the same? Or the circuit will work just as fine as simulation in physical form as well?

  • If you can show us your schematic we will be happy to check it.

    Regarding the layout, this is very important for a DC/DC.  Take a look at

    the LM2677 data sheet for a good layout example.  I have attached it here.

    Also, be sure the read the LM2678 data sheet for any tips about layout and design.

  • In reply to Frank De Stasi:

    As suggested by you I have gone through the data sheets of both IC's  LM2677 and LM2678. One difference I observed among them is SYNC pin is present in LM2677 which can be used to set oscillator frequency externally. LM2678 does not have that provision.

    I started with the following settings in WEBENCH Designer

    Then a set of options were available among those the solution with LM2678-5.0 is choosen.

    You can find the schematic below for those particular inputs with 82% efficiency for 24V nominal input.

    I tried simulating the circuit in steady state. The results for Vin and Vout are shown below:

    The thermal simulation results is also added below

    You comments will be very helpful to improve the design more. If any other IC serves the purpose better with such simple schematic, I would love to explore that option too.

  • In reply to Rajat Phate98:

    I think that the design is OK.
    You may be able to get away with less output capacitance.
    I would use the equations/suggestions in the data sheet to see if
    you could use less output capacitance. Webench may be too conservative.
    Also, you could look at the LM73605. It is slightly more complex
    but a newer device.
  • In reply to Frank De Stasi:

    Thanks, I'll try to calculate output capacitance if less value can be used.