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SND9039 LX peak voltage

Antony Lin
Genius 13480 points

Hi,

We specify the absolute rating of LX pins is 6V MAX.  Customer now get voltage level(~7V) higher than 6V for short periods.  Can you help to confirm if it's ok for us or not?

Thanks!

Antony

  • 0
    TI__Expert 5450 points

    Antony,

    7V has not been tested.  Short time it may be OK but long term reliability will suffer.  Instead the customer should check the PCB for parasitic inductance on the VIN new for the switcher that sees the high voltage spike and whether there is a way to improve it.  Since we know that this violates the PDK I would say that this is NOT OK.  It may work but we can't guarantee it.

    Chase

  • 0 in reply to Chase Maupin
    TI__Genius 13480 points
    Hi Chase,

    Customers ask if we can support to test the case of 7V, what is your comment?

    THanks!

    Antony
  • 0 in reply to Antony Lin
    TI__Genius 13480 points

    Hi,

    Additional to the LX spike voltage concern, customer also find jiter issue for buck5 (around 42% @ 5A load).  What can they do to improve this from either their schemaitcs, layout or PMIC registers?

    THanks!

    Antony

  • 0 in reply to Antony Lin
    TI__Expert 5450 points
    Antony,
    We are not planning to test above 6V as that is beyond the specification for the part.
    As for the jitter issue I will consult with our HW team and get back to you.
    Chase
  • 0 in reply to Chase Maupin
    TI__Genius 13480 points

    Hi

    Additional to the LX spike voltage concern, customer also find jiter issue for buck5 (around 42% @ 5A load).  What can they do to improve this from either their schemaitcs, layout or PMIC registers? 

    They’re using 5V as system input instead of 1S battery.  I’m not sure if it matters.

    Addititonally, they also find poor jitter performance on Intel board using our chip.


    Please see jitter plot and layout plot as attached and provide your comments what they can do to improve these.

     

                                 Test Point
    Load current

    BUCK5 LX1

    BUCK5 LX2

    0A

    0.23A

    2.5A

    5A

    0A

    0.9A

    2.5A

    5A

    Intel board(+VSYS=+3.7V)

    4.87%

    12.80%

    38.70%

    >100%

    　

    8.40%

    36.90%

    32%

    Redmond(+VSYS=+5V)

    5.90%

    14.37%

    57.80%

    >100%

    　

    10.91%

    9.95%

    46.47%

    Redmond(+VSYS=+3.7V)

    4.59%

    13.37%

    57.14%

    >100%

    　

    8.71%

    7.49%

    36.30%

     

  • 0 in reply to Antony Lin
    TI__Genius 13480 points
    Hi,

    PLease be reminded that we need layout suggestion for both jitter issue and decreasing LX peak voltage.

    THanks!

    Antony
  • 0 in reply to Antony Lin
    TI__Expert 5450 points
    Antony,
    In regards to the LX peak voltage issue if the PCB is built correctly then a Vin of 5V will work. However, if there is a lot of trace inductance on the PCB there could be issues. The recommendation is to have 1nH of inductance on the Vin side of the coverter between the PMIC and the input cap.
    Chase
  • 0 in reply to Chase Maupin
    TI__Genius 13480 points
    Hi Chase,

    Regarding the LX Peak Voltage concern, do you think it's helpful to add RC Snubber at LX pin? What is the suggested R & C value？

    Please also be reminded for the jitter issue.

    Thanks a lot!

    Antony