TPS72730 ouput impedance vs frequency

Hi Esa,

Output impedance vs frequency is not commonly measured. Please see the following article that describes how to calculate output impedance.

www.ti.com/.../slyt187.pdf

Very Respectfully,
Ryan

Hi Ryan,

Thanks for your reply and the link to the article. If we look at the equation of Zo in the article, Zo equeal Rds when the frequency is zero. Is the Rds in this case the same as load regulation specified in the datasheet, i.e. 20 uV/mA = 20 mohm for TPS727? If so, then the maximum Zo is at DC and the Zo decreases when the frequency increases. Is this correct?

Regards,
Esa

Hi Esa,

Rds can be estimated from the dropout vs output current curve.  Rds is approximately the slope of the dropout curve.

Very Respectfully,

Ryan

Thanks Ryan! A couple of additional questions:

1) Is there a minimum requirement for ESR of the output capacitor used with TPS727?
2) What is the bypass capacitor Cb in the Zo equation in slyt187 document?

Regards,
Esa

Hi Esa,

Any ceramic capacitor will satisfy the ESR requirements for TPS727.

Cb is added to help model a real capacitor (similar to the reason Resr was added).  Cb helps to better model Co across frequency.

Very Respectfully,

Ryan