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UC2843A: Induced noise

Part Number: UC2843A

Hello Team,

My Customer is having an issue with their current mode PWM controller for a buck converter. They are seeing noise being induced on the COMP pin of the UC2843A part and adding a 470pF filtering capacitor has resolved the issue. Wanted to see if you see any potential issues adding this capacitor may cause?

Regards,

Renan

  • Hi Renan,

    Thanks for connecting through to E2E. The 470 pF will impact the control loop compensation and adding any additional capacitance to COMP will result in a sluggish loop response. 470 pF is not much capacitance and may not be noticed, depending what the existing compensation looks like? Adding a 470 pF capacitor top COMP is a band-aid fix that is not addressing the root cause of the noise source. Take a closer look at the component choices, such as the reverse recovery characteristics of the buck diode, if the buck is a standard, non-synchronous type. What does the divided down feedback voltage look like – this is the inverting input to the voltage error amplifier and a likely source of noise introduced to COMP. If the divided down feedback voltage is noisy, check the AC ripple across the output capacitor bank and maybe reconsider capacitor component types/values? Revisit the PCB layout and make sure the high frequency switching GND is separate and connected by a single point only to the “quiet” digital GND.

    Regards,

    Steve