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TPS7A4001-EP: Bypass capacitor selection

Dean McPherson
Prodigy 10 points
Part Number: TPS7A4001-EP
Other Parts Discussed in Thread: TPS7A4001

Tool/software:

Hi,

I am using TPS7A4001 voltage regulator, we have designed in a 47nF capacitor for the the bypass which is connected between the feedback pin and the output as a low noise solution is desirable.

Upon review we have however we have noticed that the device datasheet recommends use of only 10nF. Are there any disadvantages increasing the bypass capacitor to 47nF? 

There are no significant transients to be concerned with for our application.

Kind Regards,

Dean 

  • 0
    TI__Mastermind 49985 points

    Hi Dean,

    I don't see any mention in the datasheet of a limitation if using a higher-valued CBYP (or a smaller one for that matter), so I don't expect stability issues if you want to use a 47nF capacitor. For the loop, increasing the size of the feedforward capacitor moves the pole and zero introduced by it to lower frequencies, so there will be an increase in phase margin at some operating loads and a reduction in phase margin at other operating loads. This is true in general when a feedforward capacitor is used. Knowing the exact effect is difficult because the bandwidth of the device is highly dependent on the load current and the loop of each device is different, but since there is no mention of stability considerations in the datasheet it's expected that the phase margin remains acceptable even when a larger feedforward capacitor is used. 

    We have an app note on this topic as well, see below. 

    Pros and Cons of Using a Feedforward Capacitor with a Low-Dropout Regulator: https://www.ti.com/lit/an/sbva042/sbva042.pdf

    Regards,

    Nick