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WEBENCH® Tools/LM25117: LM25117 VCC drop down to 4V

Yu Hsiang Shen
Prodigy 20 points
Part Number: LM25117

Tool/software: WEBENCH® Design Tools

Hi 

I am design a 120W Buck converter for the following:

Vin=20-39V

Vout=12V

Iout=10A

( See attached)

When  no load condition, output 12V,  waveform are correct

CH1: UVLO pin, CH2: SS Pin, Ch3: Vcc pin

When the output current is 2A, VCC drop down to 4V

CH1: UVLO pin, CH2: SS Pin, Ch3: Vcc pin

I have tried to connect VCCDIS to GND, but the situation did not improve,

Is there a better solution ? Please give me advice

thanks!

Austin

12V and 5V DC to DC-20170406 - .PDF

  • 0
    TI__Intellectual 2910 points
    Hi Yu Hsiang Shen,

    What is the inductor value you are using in your design?

    4.7uH corresponds to 50% of inductor current ripple - that may cause the design to hit the current limit.
    15uH usage will result in 20% of current ripple.

    It's not clear what value you are using when I'm looking at your schematics and BOM.

    Can you have a look at the voltage at CS pin to determine if the design is going into current limit or not?

    Piotr