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Original question:

Decoupling analysis and the frequency of interset.

LM63625-Q1: Frequency of interest for decoupling analysis

Shanjai kanna s
Prodigy 190 points
Part Number: LM63625-Q1

Dear Team,

While performing decoupling analysis to the processor, the following two things are important:

  1. Target impendence
  2. Frequency of interest

Where, target impedance can be calculated by current and ripple voltage.

Could you please suggest lower target frequency for Decoupling analysis with LM63625DQDRRRQ1 Part?

Thanks,

Shanjai Kanna S

  • 0
    TI__Guru 59395 points

    Hello

    You will need to give us more details about the type of analysis you are performing.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 190 points

    We are analysis Z-Parameter with respect to frequency waveform (PDN profile) for 5V0 power rails. We calculated target impendance using current and voltage ripple requirements. But, we need target frequency to verify whether PDN Profile should be below target impedance. Higher target frequency is decided based on Load IC. Lower target frequency is based on VRM. We are using LM63625DQDRRRQ1 as source for 5V0 Rail. Could you please suggest lower target frequency for decoupling analysis?

    Would you please list the further details you needed?

    Thanks

  • 0 in reply to Shanjai kanna s
    TI__Guru 59395 points

    Hello

    Let me investigate this analysis and I will get back to you by 6/23/2023 PDT.

    Also, you have a post regarding the LM63615.  We will deal with both the '25 and '15 in this post and I will close the

    other post.

    Thanks

  • 0 in reply to Frank De Stasi
    TI__Guru 59395 points

    Hello

    If you can tell me your input voltage, output voltage, and load on the regulator I may be able

    to give you some idea about the target impedance.

    Typically, we do not have a target impedance for the PDN for our converters.

    We specify input capacitor(s) that we have tested to provide a low enough impedance for the converter.

    In general, the PDN should not have any resonance between D.C. and the switching frequency, or beyond.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 190 points

    Sorry for the late reply!

    Here, we are doing decoupling analysis 5V and 3.3V power rails in which,

    • VRM is output of LM63615 and LM63625
    • Load for LM63615 is 0.59A and Load for LM63625 is 0.50A

    For LM63615,

    1. input voltage range - 10.47V to 11.78V
    2. output voltage range - 3.250V to 3.350V
    3. Load (I) - 0.59A

    For LM63625,

    1.  input voltage - 7V to 18V
    2. Typical output voltage - 5.5V
    3. Load (I) - 0.59A

    We have already calculated target impedance by using above details. But we need frequency of interest to see PDN profile. Since decoupling at higher frequencies should be taken at the die of Load IC, we considered highest target frequency as 10MHz. But We need lowest target frequency which is related to VRM inductance of LM63615 and LM63625.

    Could you please suggest lower target frequency to analyze decoupling analysis?  

    Thanks,

  • +1 in reply to Shanjai kanna s
    TI__Guru 59395 points

    Hello

    Of course you would like a low impedance all the way down to D.C.

    However, the lower edge for the loop bandwidth for this device is about 20kHz.

    So, you can use that value.

    Thanks