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CDCLVC1310: Ferrite beads recommended current rating and impedance value for CDCLVC1310, CDCLVC1104, CDCLVC1106 clock buffer ICs

Megha Agrawal
Prodigy 90 points
Part Number: CDCLVC1310
Other Parts Discussed in Thread: CDCLVC1106, , CDCLVC1104

Hi Team, 

Greetings !

I have some queries regarding the Fbead current and impedance ratings which are used to filter the power supply for  buffer ICs CDCLVC1310, CDCLVC1104 and CDCLVC1106.  In datasheet, nowhere the ratings are mentioned. 

Q1. What should be the recommended package, current and impedance rating of a FBEAD used for filtering of the power supply for 3 ICs : CDCLVC1310, CDCLVC1104 and CDCLVC1106 ?

Q2. Can the same package, current and impedence rated FBEADs  be used for all the above mentioned buffer ICs ?

Q3. In CDCLVC1310 IC Eval board, the  BOM list has the fbead of package 1206, (50 ohm impedance, 3A max current rating). For our design, If we select a fbead of package 0603 (current rating >= 3 Amp and impedance <= 50 ohm). Then which Fbead (0603 package or 1206 package ) is better to keep on the board ?

Q4. If two Fbeads have same impedance and current ratings, then which package (small or large) is better to use in the design ?  

  • 0
    TI__Genius 16845 points
    Hi Megha,

    A1. Select a ferrite bead with low DC impedance. I recommend to select a ferrite with a DC resistance of 50 ohms or less. The impedance of the ferrite bead at the clock frequency should be high. When using a ferrite bead as a power supply filter, a typical designer constraint is to use a ferrite at 20% of the current rating.

    A2. Yes, the same ferrite bead can be used with all three of these devices.

    A3. Both ferrite beads are good options.

    A4. Ultimately, the purpose of the bead is to isolate the high frequency noise. Also check the AC impedance at the frequency of interest. Use whichever package is preferred.

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    Prodigy 90 points

    Hi,

    Thanks for the solution. 

    In A1. What is meant by ferrite at  20% of current rating ? Does it mean, the device/ buffer current consumption should be less than the 20% of Fbead's current rating?

    In A4.  It is told "whichever package is preferred", then what  should be the preference criteria to select the Fbead Size ?

  • 0 in reply to Megha Agrawal
    TI__Genius 16845 points

    Hi Megha,

    In regards to A1; Yes, your understanding is correct, but this is only a design constraint.

    For A2; In general, selection criteria for the size of the ferrite bead includes:

    • Solution size (area): If you are in a space-constrained design, use a smaller package. If you anticipate a need to rework by hand (for example a test board), you may want to use components in a larger package.
    • Solution height: Similar to the previous bullet, there may be a constraint on the minimum or maximum height of a component depending on the manufacturing flow and if board rework is anticipated.
    • Power consumption: Larger packages are typically rated for higher power.

    I recommend 0603 footprint or greater if board rework is anticipated. I hope this helps!

    Kind regards,
    Lane

  • 0 in reply to Lane Boyd
    Prodigy 90 points
    Hi Lane,

    Thanks for the clarifications.