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Cff of TPS56C215

Takahiro Nishizawa
Genius 5575 points
Other Parts Discussed in Thread: TPS56C215

I have questions about TPS56C215.

In datasheet p.22~23,  I do not understand how to decide capacitance of Cff.

(In figure 29 Application Schematic, C10 is 56pF.)

Question1.

How do you decide 56pF?

Do you know the formula about Cff?

Question2.

Please tell me the standard that Cff is needed or not.

Best regards,

Nishizawa

  • 0
    TI__Expert 6425 points
    Hi,
    1, Firstly, it is recommended to refer to Table 5 in DS for reference. Secondly, Cff adds a zero that should locate around crossover freq. So you can estimate the Cff by Cff=1/(2*PI*R4*fco) (R4 is upper divider resister. The fco is usually targeted to be less than one-fifth of the switching frequency (table 1). )
    2, When Vout is small, Cff isn't need, when Vout is bigger then about 3.3V, Cff is needed.

    best regards.
    Edwin.