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TPS7A47: rms noise from 20Hz to 20,000Hz

Wayne Liu
Expert 8705 points
Part Number: TPS7A47
Other Parts Discussed in Thread: TPS7A3501

Hi,

We are designing a power supply for HiFI audio, so we need the rms noise performance in 20 to 20KHz, could you please help to provide it? I only see the noise from 10Hz to 100kHz is 4uVrms. The output current is 500mA and voltage is 5V. Thank you.  

  • 0
    TI__Guru 50090 points

    HI Wayne,

    In the datasheet figure 1 shows the graph of noise measured out to 1MHz.

    In the below, I tried to highlight the area under the curve which is the RMS noise:

    You are correct in that the noise from 10 to 20Khz would be lower, but it would be lowering only by the amount shown in red below:

    So the reduction would not be large at all. Without re-taking the measurements this could possibly round down to 4.6uVrms.

    Does this help or did I mis-understand your question?

    Regards,

  • 0 in reply to JCHK
    TI__Expert 8705 points

    Hi JC,

    Thank you for your help. Yes you well understand my question.

    However, You draw a picture from 10 to 20KHz, what I need is 20 Hz to 20KHz, and I posted a same question for TPS7A3501 as below, Ryan gave me an exact number for the noise, appreciate if you also can give me the exact number.

    Ryan Eslinger replied to TPS7A3501: RMS Noise in 20 to 20,000Hz.

    Hi Wayne,

    The noise is 2.47uVrms for 20 to 20kHz.

    Very Respectfully,
    Ryan

  • 0 in reply to Wayne Liu
    TI__Guru 50090 points

    HI Wayne,

     

    I apologize for oversimplifying and missing that the bottom of the noise chart was not 0.  Based on the PDS, I can only estimate the noise contribution over frequency. Ryan can actually measure it as he has the lab access.

    That being said, the noise reduction would be on par with the TPS7A35.  We need to measure to give the exact number.

    Regards,

  • 0 in reply to JCHK
    Prodigy 20 points
    Hi JC,

    The noise of 4701 is rather low. In the Graph in the datasheet, it seems that you measure the noise with a Spectrum Analyzer. Which model do you use for this measurement? The one we have is KEYSIGHT N9020A, which has a noise floor of -120dBm(0.22uV)@100kHz with RBW set as 10Hz. This is larger than the results in your datasheet.
    It seems that pre-amplifiers are usually used for low noise measurement. But since noise of 4701 is raher low, the noise of the pre-amplifier may be on the same level.
    So can you give me some suggestions for measuring noise like 4701?
    Thanks!

    Regards,
    Yu-Meng
  • 0 in reply to user5006612
    TI__Expert 7015 points

    Hi Yu-Meng,

    To make our noise measurements we use the HP4395a, and use the measurement method described in this white paper:

    If you use an amplifier to boost the signal further above the noise floor of the Spectrum Analyzer you will get a better measurement. You will also want to make sure that your input supply is not contributing to the noise of the LDO. You may have to use a filter to get an accurate measurement of the LDO noise.

    One more thing you can try is reducing your RBW at low frequencies. Reducing your RBW for the first couple of decades in your measurement may help as well.

    Best Regards,

    Mark

  • 0 in reply to Mark Sellers
    Prodigy 20 points

    Thanks! The document is useful.

    Best Regards,

     Yu-Meng