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TPS7A8300: why Cff can improve low frequency noise performance

Meng Liu
Intellectual 1765 points
Part Number: TPS7A8300

Hi Expert

In my understood, At higher frequencies, VFB and VOUT are effectively shorted by CFF, which prevents the reference noise from being increased by the gain of the error amplifier.so Cff can improve high frequency noise performance but in fact, Cff improve low frequency noise performance. 

how to understand this phenomenon？

  • +1
    TI__Expert 6825 points

    HI Meng,

    I typically agree with your statement that the CFF should prevent the reference noise from being gained up and improves high frequency performance for typical CFF values. The issue here is that this CFF is 10uF so it is creating a very low frequency low pass filter here and is causing the noise to decrease from the very beginning of the measurement. For typical values like 100nF and 10nF it will have a mid frequency to high frequency effect though.

    Regards,

    Mark