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TPS7A8300: About out put cap

Tsukui Yusuke
Guru 21930 points
Part Number: TPS7A8300

Hi,

Let me talk about the output capacitor of TPS7A8300.
Is the characteristic(PSRR) different between using a tantalum capacitor as the output capacitor and using a ceramic capacitor?
Also,Does PSRR improve if increasing the output capacitor?
The data sheet contains only the following contents.



Could you tell me the combination of TPS7A8300 and output capacitor that improves PSRR.

Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Genius 13085 points
    Hi Yusuke,

    Yes, there will be slightly different PSRR performance in the high frequency range beyond the LDO's bandwidth. The differences in performance comes from the the differences in the impedance vs frequency that the two types of capacitors have. The lower the impedance of the capacitor the higher the PSRR. What you'll see is ceramic capacitors tend better PSRR performance due to their lower impedance at the resonant frequency, which is due to the lower ESR inherent with ceramic caps.

    As for PSRR performance versus output capacitance value, a larger output cap will increase the PSRR performance (in the high frequency range) due to the lower impedance. It will also shift the resonant frequency to a lower frequency which occurs at 1/(2*π*√(C*ESL)).

    One important note is that the TPS7A8300 is designed to operate a ceramic capacitor of 22uF or larger. If you wish to also add a tantalum capacitor to the output that is ok, but it must be in parallel with the ceramic capacitor. But as I noted above in general ceramic capacitors are better for PSRR due to their lower impedance.

    -Kyle