• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 34 subscribers
  • Views 129 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DP83822HF: Questions regarding DP83822IF 100BASE-FX and SFP interface for EtherCAT

HARUTO SHIMIZU
Prodigy 10 points

Part Number: DP83822HF
Other Parts Discussed in Thread: DP83822IF, DP83822EVM, , TMS320F28388S, MSP430F5529

Hello,

I am currently designing an EtherCAT interface using the DP83822IF and 100BASE-FX, and I am referring to the DP83822EVM schematic and layout as a reference for my circuit design.

I have two questions regarding the 100BASE-FX interface.

1. PHY used on the DP83822EVM

According to the DP83822EVM documentation, the EVM supports 100BASE-FX.

However, when I checked the schematic/BOM, the PHY part number appears to be different from the Fiber-supporting variants of the DP83822.

Could you please clarify:

  • Which exact PHY part number is actually mounted on the current DP83822EVM?
  • Is the PHY mounted on the EVM capable of supporting 100BASE-FX?
  • If the part number shown in the schematic/BOM differs from the actual mounted device, which device should be considered the reference for 100BASE-FX operation?

2. AC coupling capacitors between the PHY and SFP

In the DP83822IF datasheet, AC coupling capacitors are shown on the TX/RX differential signal lines for the 100BASE-FX interface.

However, I do not see these capacitors between the PHY and the SFP connector in the DP83822EVM schematic.

Is my understanding correct that these capacitors are not required on the EVM side because the SFP module used for the EVM already has the AC coupling capacitors internally?

For my EtherCAT design, if the selected SFP module has internal AC coupling capacitors, is it correct that additional AC coupling capacitors do not need to be placed between the DP83822IF and the SFP connector?

If this depends on the SFP module, could you please let me know which SFP specification or documentation should be checked to determine whether the AC coupling capacitors are internally included?

Thank you for your support.

  • 0
    TI__Mastermind 44975 points

    Hello,

    The EVM currently have the -HF variant available. With the "F" suffix, it will be able to support 100Base-FX. 

    Your understanding is correct. Typically SFPs have AC coupling in-built tot he module. 

    Sincerely,
    Gerome

  • 0 in reply to Gerome Cacho
    Prodigy 10 points

    Hi Gerome,

    Thank you for your detailed answers. They were very helpful.

    First, I would like to correct one point from my previous post.

    I mentioned DP83822IF, but I made a mistake. We are actually planning to use the DP83822HF for our design.

    I have one more question regarding our planned system configuration.

    We are planning to use two DP83822HF PHYs for the two EtherCAT ports (IN and OUT) with the following configuration:

    • MCU: TMS320F28388S
    • PHY: DP83822HF × 2
    • Optical interface: 100BASE-FX SFP × 2
    • Application: EtherCAT
    • The two PHYs are used for the two EtherCAT ports (IN and OUT).

    Would this hardware configuration be suitable for an EtherCAT application from a hardware perspective?

    In particular, are there any known hardware-related issues or limitations with this configuration that we should be aware of?

    Thank you again for your support.

    Best regards,
    Haruto Shimizu

  • 0 in reply to HARUTO SHIMIZU
    TI__Mastermind 44975 points

    Hello,

    This looks fine. TMS320F supports a 2 port ECAT channel which is where 2x 822's will be attaching on the MAC interface. I would recommend procuring a DP83822EVM to validate all your FX functional needs along with an MSP430F5529 to program the SMI.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    Prodigy 10 points

    Hi Gerome,

    Thank you very much for your quick and detailed support.

    Your answers have clarified our questions and helped us confirm our hardware configuration.

    I really appreciate your support.

    Best regards,
    Haruto Shimizu

  • 0 in reply to Gerome Cacho
    Prodigy 10 points

    Hi Gerome,

    I have one more question regarding the resistors in the fiber interface.

    In the DP83822 datasheet, Section 9.2.2 “Fiber Network Circuit,” 49.9-Ω pull-up resistors are connected to each of TD_P, TD_M, RD_P, and RD_M.

    However, in the SFP specification (INF-8074i), a 100-Ω resistor is placed between RD+ and RD-, and there are no 49.9-Ω pull-up resistors as shown in the DP83822 datasheet.

    Are these resistors intended to serve the same purpose?

    Or should both the 49.9-Ω pull-up resistors and the 100-Ω resistor be included in the circuit?

    Thank you for your support.

    Best regards,
    Haruto Shimizu

  • 0 in reply to HARUTO SHIMIZU
    TI__Mastermind 44975 points

    Hi Shimizu-san,

    The 49.9 ohm PUs are required for the current mode drivers within the DP83822. Please consider this as part of the SERDES IC block itself if reference Figure 2B in 8074i.

    Sincerely,

    Gerome