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Inquiry for DP83630 ANA33VDD voltage supply

Atsushi Okui
Genius 4015 points

Other Parts Discussed in Thread: DP83630, DP83640

Hello, all.

 

Now I am doing hardware design with DP83630 for our PLC system.

 

I am referring your schematic of DP83640 TP&FX Demo Board for this design. (Document No.870013211-200).

 

I would like to know about the detail on voltage supply into ANA33VDD pin.

 

As far as I could see on the schematic, the 3V3 line is combined with VCT, then supplied into ANA33VDD pin.

This 3V3 line is also supplied into IO_VDD or other digital interface line.

 

However, based on our experience, the analog supply line is isolated from digital supply by ferrite bead.

 

Please let me clarify whether the voltage supply line could be commonly used on both analog and digital supply line for DP83630.

 

Thank you in advance for your information.

 

Best regards,

  • 0
    TI__Intellectual 1885 points

    Hello Atsushi-San,

    The schematic for the DP83640 TP & FX Demo Board uses 0 Ohm resistors as placeholders for ferrite

    beads in the ANA33VDD and the IO_VDD supply lines. Both of these supply lines are sourced from 3V3.

    The schematic also uses a 0 Ohm resistor between 3V3 and VCT. These 0 Ohm resistor can be replaced by ferrite beads

    if needed to meet system EMI requirements.

    The Application Note, AN-1469 PHYTER Design and Layout Guide section 4 addresses this issue. Please see

    text below.

    "The device Vdd supply pins should be bypassed with low impedance 0.1 μF surface mount capacitors. To

    reduce EMI, the capacitors should be places as close as possible to the component Vdd supply pins,

    preferably between the supply pins and the vias connecting to the power plane. In some systems it may

    be desirable to add 0 ohm resistors in series with supply pins, as the resistor pads provide flexibility if

    adding EMI beads becomes necessary to meet system level certification testing requirements."

    A common supply for analog and digital can be used if the recomendations of AN-1469 are followed.

    Regards,

    John

  • 0 in reply to John Hamilton1
    Genius 4015 points

    Hello, thank you for your prompt reply.

     

    I would like to make sure regarding the case that 0ohm resistor or ferrite bead need to be placed on both ANA33VDD and VCT sourced from 3V3 each other, since we thought these lines are same category as analog supplied pin.

    Please let me know on which case are these pins need to be isolated each other.

     

    Thank you once again for your information.

     

    Best regards,

  • 0 in reply to Atsushi Okui
    TI__Mastermind 31600 points

    In most applications, the desired functionality can be achieved without adding ferrite beads to isolate ANA33VDD or VCT 

    Typically we recommend against adding a ferrite bead to isolate VCT.  In most applications, the best performance is achieved using a direct connection for VCT. 

    If system noise is especially high, it may make sense to add a ferrite bead to isolate ANA33VDD. 

    We have several recommendations on reducing EMI in application note AN-1862 (Literature Number:  snla107).  It is available at:

    http://www.ti.com/litv/pdf/snla107

    Patrick