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DS92LV2412: Recommended decoupling capacitor value

Kawai
Guru 19775 points
Part Number: DS92LV2412
Other Parts Discussed in Thread: DS92LV2422, LV24EVK01

Hi Team,

I see two description for DS92LV2412 deserializer power pins decoupling capacitor recommendations.

1). DS92LV2412 Datasheet page 42, Figure 36 : Only have 0.1uF on most of the power pins.
     --> DS92LV2422 seems to have same description, too)

2). LV24EVK01 : EVK had 22uF, 0.1uF, and 0.01uF on most of the power rail.

Which of above is TI recommendation ? In which condition is the device tested ?

If 2) is your recommendation, please advise us how to place the 3 caps to VDDIO (3 pins) and VDDSC (2 pins).

Best Regards,

Kawai

  • 0
    TI__Mastermind 35130 points
    Hello Kawai-san,

    Is this related to the device not locking? Please reference this thread: e2e.ti.com/.../217715 particularly the last page, where capacitor recommendations are discussed.

    Regards,
    I.K.
  • 0 in reply to Ikechukwu Anyiam
    Guru 19775 points
    Hi I.K.-san,

    Yes, it is related to my another post.
    e2e.ti.com/.../2534223

    It may be a tough question, however, could you please tell us one by one for the following questions ?

    1). What are the decoupling capacitor conditions which tested at TI ?

    2). How could user judge if he has enough decoupling caps.

    3). How could user know how much margin he has ?

    Best Regards,
    Kawai
  • 0 in reply to Kawai
    TI__Mastermind 35130 points
    Hello Kawai-san,

    I will check with the people that previously supported this device and see if I can provide some information to you by the end of this week.

    Regards,
    I.K.
  • 0 in reply to Ikechukwu Anyiam
    Guru 19775 points

    Hi I.K.-san,

    We greatly appreciate for your support. I look forward to hear from you soon.

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Mastermind 35130 points
    Hi Kawai-san,

    I believe this was handled over email. Below is the answer given:

    There are no concerns about 9MHz particularly. For the supply noise, normally we would prefer to have it below 20mV typically. With a 10uF cap and ferrite beads, normally the noise is way below this figure. This device was tested with the LV24EVK, and most of the power rails have a 22uF, 0.1uF, and a 0.01uF cap because if this unlock issue was seen it 100% would have been addressed right away. We have been using 20mV for our high speed devices, and have tried to recreate 20mV noise with normal supply coupling caps but it is very difficult because supply coupling caps act like a low impedance to ground. Also, LDO switching frequency should be above loop bandwidth of the data rate. This way, the device loop filter can attenuate this noise.

    In summary, adding a lot of supply caps , ferrite beads, and a correct choice of LDO can take care of this issue.

    Regards,
    I.K.