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LM3478 Boost Controller - adding capacitor to feedback resistor Rf2

Shane Hanna
Prodigy 60 points
Other Parts Discussed in Thread: LM3478

I am designing a LM3478 (12V/20V @4A, 560KHz) circuit to power a Li-ion Battery Management IC. An independent review of my design suggested that I place a 100pF (not a feed forward capacitor) across Rf2 (to GND) to reduce noise. I say adding a capacitor will introduce another pole and zero and will adjust the phase margin and cross-over frequency. Am I correct? Can anyone recommend or not recommend adding a 100pF capacitor to the feedback loop? Please advise. Thank you.

  • 0
    TI__Expert 4015 points

    You are correct that adding a capacitor will introduce an extra pole into the system. It won't introduce an extra zero. 

    In general it is high frequency noise which people are worried about in electronic circuits, as this noise couples more effectively from one node to another. As such the filter to remove it can have a high corner frequency. If you add a small capacitor, such that the filter it forms with the feedback network has a corner frequency of more than 10x the highest 0dB crossover frequency of the loop, then it will not impact on the loop response in the area of interest to the system.

    Hope this helps.

    Thanks

    Billy 

  • 0 in reply to Billy Long
    Prodigy 60 points
    Thanks for your feedback. It is very helpful.

    Shane