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TPS79601 vs. TPS79630 output noise

John Carpenter50292
Prodigy 30 points

I would like to know the output noise of the adjustable version of the TPS796xx LDO regulators (TPS79601).

All figures and tables of the datasheet are referred to TPS79630, with the different values depending on the CNR capacitor value (used to reduce the noise due to the internal voltage reference). But there is no noise data regarding the TPS79601.

Adjustable version does not have the CNR capacitor (this pin is used for feedback resistor network to adjust the output voltage), so I think noise it's worse in TPS79601. Am I right?

Best regards

John

  • 0
    TI__Expert 8890 points

    Hello John,

    Yes, the noise will definitely be worse for the adjustable version without a noise reduction capacitor.  The noise for the adjustable version will be dependant on size/value of the divider resistors and whether or not a feedforward capacitor is used across the upper resistor.

    Let me research this question for a day to see if we have any data that might help you.

    Regards

    Bill

     

  • 0 in reply to Bill Stokes
    Prodigy 30 points

    Hello Bill,

    The upper resistor is 30Kohms and the lower resistor is 20Kohms. Feedforward capacitor across the upper resistor is 24pF.

    Best regards

    John

  • 0 in reply to John Carpenter50292
    Prodigy 30 points

    Hello Bill,

    How is the research of my question?

    Best regards

    John

  • 0 in reply to John Carpenter50292
    TI__Expert 8890 points

    John,

    Unfortunately, it seems that we do not have plots of the output noise spectrum either for the adjustable version or for any fixed version without a noise reduction capacitor.    You can see the general trend in the noise as output capacitance changes and as the noise reduction capacitance is reduced from Fig. 4-6  on the data sheet.  The noise will increase for the adjustable version above that for the Cnr = .001uF (Fig. 6) but then it might be mitigated somewhat by using a small feedforward cap across the upper feedback resistor (1nF).

    Regards

    Bill