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LMR12020 Issue

Teach Me
Expert 1940 points
Other Parts Discussed in Thread: LMR12010

Hi,

I encounter an issue in  power system design, enclose is the schematic design of LMR12010 20Vin,1A step down voltage regulator.

The issue is I can’t get the correct output voltage(3.3V) while I having 12V input voltage, below is my part list.

 

C18 – 10uF 25V

C19 – 0.01uF 25V

C20 – 10uF 6.3V

R6 – 100k ohm

R7 – 31.6k ohm

R8 – 10k ohm

L1 – VLCF5028T-2R7N1R8-2, INDUCTOR, 2.7UH, 1.82A, 30%

D2 - MMSD4148T1G, diode

http://www.onsemi.com/pub_link/Collateral/MMSD4148T1-D.PDF

D3 - MBRA120TRPBF, Schottky Diode

http://my.element14.com/vishay-semiconductor/vs-mbra120trpbf/diode-schottky-1a-20v-sma/dp/8660409

U4 – LMR12010

http://www.ti.com/lit/ds/symlink/lmr12010.pdf

 

Please kindly advise us on this issue.

  • 0
    TI__Genius 15810 points

    Please send us the board layout images and some scope shots of the switch node (pin 6), VOUT, VIN and BST (pin 1). We will forward your question to the right team.

  • 0 in reply to Akshay Mehta
    Expert 1940 points
    Hi Akshay,

    Our side already solve the problem.
    Thanks for the assistant provided.

    The boost function control the internal NMOS control switch.
    As your connection is where the Vboost is derived from the input voltage Vin.
    In order to properly drive the internla NMOS switch during on-time, please follow the spec as in datasheet.

    1. Vboost > 1.6V Vsw @ Vboost >2.5V or greater Vsw
    2. Vboost - Vsw should not exceed max limit of 5.5V (important)