How to connect PHY W500 to IP175 Ethernet Switch without transformer (transformeless)?

Intro

If you use any Ethernet PHY with any MCU like STM32, ESP32 you have only one port (like SPI IC W5500) and want to increase quantity of ports you need to use Ethernet switch (like IP175G 5-port).

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The simplest method is to use standard transformer, but for board and schematic optimization I'll show how to connect it without transformer using capacitors (transformerless).

Schematic

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Pull-up resistors 49.9 Ohm only on the TX side of W5500
DC blocking capacitors 2.2nF-6.8nF on both TX and RX lines

Connected directly since IP175 support Auto MDI-MDIX function:

  • TXN -> TXOM0
  • TXP -> TXOP0
  • RXN -> RXIM0
  • RXP -> RXIP0
Use any port of IP175 (in my case it's PORT0)

Oscillograms

YELLOW — from W5500

BLUE — from IP175 (port)

Router not connected to the switch

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Router connected to the switch
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Real-time oscillograms

RJ45 not connected to the portRJ45 connected to the port
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Note: the signals could be another, depends on the working mode

References

Link saved to Internet Archive:

  1. How to use the Wiznet io-module without Transformer [PDF copy: How to use the Wiznet io-module without Transformer — Hackster.io_20250113.pdf] — https://www.hackster.io/jaden2/how-to-use-the-wiznet-io-module-without-transformer-11b310
  2. A Transformerless PHY to PHY Connection – Success (Sort of) — https://hackaday.io/project/195961-integrated-hub-ethernet-usb-rs232/log/230085-a-transformerless-phy-to-phy-connection-success-sort-of
  3. REV00 -> REV01 Fixes — https://hackaday.io/project/195961-integrated-hub-ethernet-usb-rs232/log/233512-rev00-rev01-fixes

Conclusions

  • Other Ethernet switch IC may need pull-ups of their data lines (IP175G doesn't need it)
  • Termination resistors already built-in IP175, so don't need it
  • Small tip: since IP175 always connected to the W5500 the link status will be always TRUE, so connect and read LINK_LEDx of the switch to have status of every port.

Another tip:

When design your device pay attention at the operation temperature of the IC:

  • IP175G/GH: QFN-48 (6mmx6mm), 0~70℃
  • IP175GHI: QFN-48 (6mmx6mm), -40~85℃
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