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TPS7A90: Difference between PSRR and spectral noise density

Lee, Sam
Expert 4965 points
Part Number: TPS7A90
Other Parts Discussed in Thread: TPS7A47, TPS7A83A

Hi team,

 

A customer has some questions about spectral noise density in the datasheet of TPS7A90. Could you please answer the followings?

  1. Can you explain the meaning of spectral noise density?

  2. There are PSRR and spectral noise denisty as parameters that explain the noise characteristics in TPs7A90 datasheet. How do the two parameters differ?

  3. Is PSRR and spectral noise density independent of each other? In general, if the PSRR is good, does the spectral density have a good performance? Ohterwise, are the parameters independent of each other?

  4. If two LDOs ahve similar PSRR performance and one LDO has poor spectral noise deisty, how does the output noise analyze?

 

Thanks,

Sam Lee

  • 0
    TI__Guru 55940 points
    Hi Sam,

    Noise spectral density is the measurement of the power of the noise over frequency.

    PSRR is a measurement of the ability of the LDO to block ripple coming from the power supply to the LDO (ripple at Vin) from passing through to the load of the LDO (ripple at Vout). Noise in terms of an LDO is the noise on the output of the LDO generated internally by the LDO. Noise primarily comes from the reference of the LDO. The following articles go into a bit more information:

    www.ti.com/.../slyt201.pdf

    www.ti.com/.../slyt202.pdf

    PSRR and noise are independent of each other. Having a high PSRR device does not necessarily mean you will have a low noise device; however, high performance LDOs such as TPS7A47 and TPS7A83A will generally have both low noise and high PSRR.

    Very Respectfully,
    Ryan