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TPS23861: TPS23861 does not work. Question of center tap connection.

Part Number: TPS23861
Other Parts Discussed in Thread: TIDA-010046


I designed a PSE circuit using TPS23861 and KSZ8041
Even if you connect to a hub (that is not PD), it will not link up.
For the connection between the transformer and the connector from TPS23861, I referred to TIDA-010046, but
I don't know if the correct connection is that 3.3V is not connected to the CT on the PHY side.

(1) Is there any problem because 3.3V connection to PHY side CT is unnecessary?
If the PHY is an MLT-3 current output, we believe that 3.3V is required.

(2) Is there any problem because the PHY side terminating resistor (49.9Ω x 2) is unnecessary?

TIDA-010046 Circuit diagram (P.3)

  • Hi User,

    I'm more familiar with the power side of PoE and not so much the data side; however, I will say that the center tap connections on the data side are determined by the PHY datasheet. Looking at the TPS23861 design, it looks okay to me. This is pointing toward more of the PHY. You can also check that your PD you are connecting to is receiving the ethernet data through pairs 12/36 like shown in the reference design. If it's the other pair set (Pairs 45/78), then there's no way for the data to get to the PD. This might be good to double check. If it is the PHY then I recommend checking with the competitor's support engineer since i'm not familiar with this part as I wasn't able to find the required center tap requirements in its datasheet. I hope this helps. Thanks!

  • thank you for your answer.

    It turned out that the center tap on the data side depends on the PHY.

    I contact the PHY manufacturer and check the connecting .

    By the way, when designing a POE circuit, should the PHY be selected to support 802.3af or later?
    The TIDA-010046 PHY: DP83825IRMQR was IEEE 802.3az, while the KSZ8041 was IEEE 802.3u.
    Can I use POE?

    Thank you.

  • Hi User,

    One advantage of PoE is that the data and power are independent of each other. So really, the PHY selection should NOT be dependent on the PoE standard (power level) you implement. What matters is the data transformer selection. The data transformer should be able to accommodate the power level and the ethernet data rate. Please let me know if this helps. Thanks!

  • Thank you.
    I was able to understand with your answer.