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PMP7499 Circuit Design

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: PMP7499

I would like to ask about PMP7499 circuit design.

In the PMP7499 schematic (slvrb55), there is no termination circuit at the PoE+ magnetics center tap of data port side. Is there any reason why there is no? Isn't it needed? or should the customer set the termination circuit?

And also, about ETHERNET POWER port side center tap termination circuit, how can we decide these R, C component value and voltage and power rating? (It is 0.01uF/100V, 1000pF/2kV and 75ohm/ 1/16W)

Best Regards,

Kohei Sasaki

  • 0
    TI__Mastermind 42795 points

    The data side of T1 and T2 (and even the vendor/type of T1/T2) depends on the ethernet PHY used. Many times, the PHY will provide a suggested data transformer type and vendor as well as how to terminate the center taps for their PHY. Since PMP7499 is a "generic" PD we left the CT's open.

    The Bob Smith termintors (C1-C4, R4-R7) are fairly standard ethernet cable terminations for both the PD and PSE side. Sometimes (depending on equipment vendor) the capacitor values will change slightly (22nF instead of 10nF) but do have an effect on the overall port capacitance which for the PD side should be less than 120nF.

    C6 must have a breakdown of > 1500V to meet the POE standard and 1000pF, 2kV is a common value. Sometimes this value is increased depending on what types of EMC issues are found in the end product.