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LM51551-Q1: Accuracy for LM5155Q1 Design

Sreenath Chatterjee
Prodigy 120 points
Part Number: LM51551-Q1
Other Parts Discussed in Thread: LM5155-Q1, LM5155

Hello,

This is Sreenath, and my question is that I used the Webench Design tool to make a Circuit design for LM5155-Q1.

My needs were 3.3v input to 16v Output at 4amps, so after trying the Webench tool, I got this Design. (Image Attached)

So, my question is that how accurate will it be if I make it a final product.

and the second Question is the Mosfet used is generating a heat(as per Webench) which is about 85`C,,,, So how can that be reduced.

Thank You.

  • 0
    TI__Mastermind 21720 points

    Hi Sreenath,

    Thanks for reaching out with your question and for considering the LM5155 in your design.

    The WEBENCH model should be fairly accurate, as always the design should be evaluated thoroughly after it is built. One quick question, what is the minimum input voltage and maximum input voltage for your deisgn?

    The MOSFET losses can be reduced by selecting a MOSFET with lower RDSon and lower gate charges.

    Thanks,

    Garrett Roecker

  • 0 in reply to Garrett Roecker
    Prodigy 120 points

    Thank You Sir,

    Its nice to hear such accuracy of it.

    The minimum input voltage is 3.3v and Maximum input voltage is 7.4v, but the input voltage that I will be sticking around will be 3.7v Li-On battery (18650.)

    So, sir could you specify which MOSFET can be used, with a build number?

    Thank You.

    Sreenath

  • 0 in reply to Sreenath Chatterjee
    TI__Mastermind 21720 points

    Hi Sreenath,

    If the input voltage range is this low I would suggest connecting the VCC pin and BIAS pin together in your schematic. This will allow the LM5155 to operate down to 2.97V. this will give you a little bit more margin base on your minimum input votlage.

    Regarding the MOSFET, I suggest finding a logic level MOSFET with a low gate threshold as the input voltage for this application is pretty small. The other two parameters that should be considered are the RDSON and the and the total gate charge, which effects the MOSFET conduction losses and the switching losses, respectively. I'm not sure what MOSFET is suggested in WEBENCH but if you can find a MOSFET with lower RDSON and gate charge the power dissipation in the MOSFET should be lower.

    Thanks,

    Garrett