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DS90UR241/124 - External Bypass capacitor

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: DS90UR241, SERDESUR-43USB

Hello,

In DS90UR241/124  datasheet page 30, there is the discription of the "External bypass capacitors should include both RF ceramic and tantalum electrolytic types".


(1)  Tanatalum electrolytic cap
Can I use ceramic capacitors instead of tantalum electrolytic types?

Since the datashee was published on 2006, I think that the datasheet use tantalum type because the ceramic capacitors DC rating was small on 2006.
However, the ceramic capacitors DC voltage rating is increased by technologyadvance.
Thus , we can choose the ceramic capacitors which has the range of 2.2uF to 10uF with 5xPower supply voltage rating.

(2)Typical application connection
I can't found the 2.2uF to 10uF capacitors in the typical application connection Figure 22 and 26.
Please let me know this reason.

(3) User's guide schematics
In the SERDESUR-43USB User's guide page 25, there is the bypass capacitors combination as 0.01uF and 0.1uF and 22uF.
Why does this schematic use 22uF as a bypass capacitor?
The datasheet recommendation capacitor range is 2.2uF to 10uF.

Best Regards,
Ryuji Asaka

  • 0
    Guru 20090 points
    Hello SDS team,

    I'm looking forward to the reply.

    Best Regards,
    Ryuji Asaka
  • 0 in reply to Ryuji
    Guru 20090 points

    Hello,

    I'm looking forward to the reply.

    Best Regards,

    Ryuji Asaka

  • 0
    TI__Expert 4210 points

    1) The capacitors are just used for local power stabilization so a ceramic capacitor is fine to use.

    2) The amount of decoupling and value may be different for each application but must meet the <+/-100mV noise spec.

        The values recommended are general guidelines to start off with.  In the pcb prototype phase, the cap value(s) may need to be tweaked depending on what power noise are found on the board, meaning other active components may cause the power noise to exceed our noise spec.

    3) Common practice is to use a few decade spread of cap values to cover a wider range of frequencies. The EVM has the 22uF to provide the maximum decoupling and show the physical layout of such a large package.  The datasheet is more of what more likely what a user value range will be used.

    Best regards,

    Darryl