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LM62440-Q1: Buck is running on 100% duty cycle

Part Number: LM62440-Q1

Hi, 

I have a problem where the buck seems to only be running on 100% duty cycle.

Have tried two different PCBs and different loads/ input voltages  

See the pictures of the schematic and oscilloscope below. 

The following pin Voltages were measured with a multimeter:

1: 12.01V

2: 3.33V

3: 0V

4: 2.36V

5: 0V

6: 0V

7: 11,97V

8: 12.09V

9: 0V

10:12.01V

11: 0V

12: 12.01V

13: 14.45V

14: 14.45V

oscilloscope view of start up

oscilloscope view while running

oscilloscope measurements while running 

layout (can also see the oscilloscope connection wire in green)

schematic

  • Hello Josef,

    After reviewing your schematic it appears you have 100k for the top FB resistor and 4.9k for the bottom FB resistor.  please refer to the output voltage setting to program the output voltage you require as it appears right now you have set the VOUT to a higher voltage than your VIN voltage.

    Hope this helps?

    David Baba

  • Hi David,

    Thanks for your help, I did just find out that by mistake I did buy the constant 3V3 Buck instead of the variable. After removing the FB resistors and connect the Inductor "output" directly to FB the buck did output 3V3.

    Sorry for the inconvenience.