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LM5085-Q1: Variable resistor in feedback loop for changing Vout

user5220573
Prodigy 10 points
Part Number: LM5085-Q1

Greetings,

I am designing a power supply with 12V input using LM5085-Q1 chip. Nominal output for the power supply should be 9V, but also I would like to place a variable resistor in a feedback loop so I can change the output voltage from 9V up to 12V (or as close to 12V as it can get). Are there any potentially unstable situations that I should consider, especially while using a configuration of duty cycle near 100% or 100%?

Best regards.

  • 0
    TI__Mastermind 26590 points

    Hello,

    As long as your input voltage is stable, the switcher should be stable.  If you plan to adjust Vout while operating, I would use a summing resistor into the FB node and control Vout with a DC voltage.  Otherwise Changing the bottom FB resistor should be just fine.  Make sure you pay close attention to the layout guidelines.  I have added some of my own for your to follow in attached.

    LM5085 Floor plan.tif

    Hope this helps?

    David.