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LMR62421 feedback capacitor

c64
Intellectual 480 points
Other Parts Discussed in Thread: LMR62421

Hi,

I designed a DC-DC solution using the LMR62421, and just got the PCBs back from the producer. However, seems like I've made a mistake and forgot to include the feedback capacitor which is supposed to connect Vout with the feedback pin on the DC-DC IC. What are the consequences of this? Might it still work? I haven't assembled the components on the PCB yet, wondering if I should do that, or simply get a new PCB produced.

Thanks!

  • 0
    TI__Mastermind 19891 points

    Hello Tomas, 

    You may have stability issues if you omit this capacitor. The suggestion would be to add the cap to your circuit. 

    Depending on your schedule, you may want to build the circuit with your existing board and try to fit both the top feedback resistor and the capacitor on the same footprint. You can choose a smaller case size components so they fit on the original pad or try to stack them on top of each other. You can also try to solder a small leaded capacitor that would fit across the top feedback resistor. That way you can at least verify the circuit before you fabricate another board and see if you need to make any other changes. 

    Regards, 

    Denislav 

  • 0 in reply to Denislav Petkov
    Intellectual 480 points

    Hi,

    Yes, that's what I was thinking about. I have a 0201 feedback resistor, and figured I could try and mount a 0201 220 pF cap on top of that.