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TPS55330: TPS55330 work abnormal, does not match the formula

Lee Jeff
Prodigy 20 points
Part Number: TPS55330

Hi
I got a problem
Calculate according to the formula
Input 12V, require output 16V, circuit as picture
But the output is 19V, no matter if R175 is 120K or 100K
Where is the problem?
Thank you

1.229V x (R175/R177 +1)

  • 0
    TI__Mastermind 34231 points

    Hi Jeff,

    Can you share the layout?

    Have you tried applying a load at output? Will the output voltage sitill be 19V?

  • 0 in reply to Zack Liu
    Prodigy 20 points

    In fact, I made a mistake.
    My original design is wrong.
    So change to external parts for experiment.
    Layout as picture.
    Thanks

  • 0 in reply to Lee Jeff
    TI__Mastermind 34231 points

    Hi Jeff,

    I didn't find the detailed datasheet for inductor MSPI0530-1R0M, please make sure the inductor has enough saturation current spec. 

    The shared layout picture doesn't show me the position of output capacitors. Please make a note on above picture.

    Below is the recommended layout in datasheet. The output capacitors are suggested to put close to cathode of Schottky diode and IC PGND pins so that the PCB parasitic inductance is the minimum. Meanwhile, the power traces should be wide enough. 

    Lastly, check the FB pin voltage to AGND with a DMM. It should be 1.244V.