---
title: "RJ45 Differential Pair Design Issues on Custom W5500 PCB"
url: "https://maker.wiznet.io/forum/15766"
markdown_url: "https://maker.wiznet.io/forum/15766/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "aravi_iot"
created: "2025-06-16T19:10:04+09:00"
last_activity: "2025-06-17T20:21:58+09:00"
language: "en"
tags: ["ESP32", "W5500"]
views: 5
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# RJ45 Differential Pair Design Issues on Custom W5500 PCB

## Question

Asked by aravi_iot on 2025-06-16 in Ethernet Chips.

Hi,

I'm designing a custom Ethernet module using the W5500 chip and a MagJack (RJ45 with integrated magnetics - **HR911105A**). I'm seeing no Link/ACT LEDs lighting up when an Ethernet cable is connected, even though SPI communication with the W5500 works fine.

I suspect this might be due to incorrect differential pair routing or transformer connections. Here are my questions:

- How should the differential TX+/- and RX+/- pairs be routed from the W5500 to the RJ45 jack?

- Should they be length-matched?

- What impedance and spacing should be maintained?

- How to check this issue in Kicad IDE

Are these common mistakes in transformer (CT, center tap) connections or polarity that could lead to Link LEDs not turning on?

Can you check this portion of my schematic/layout for potential differential signal integrity issues? (I can share an image if needed)

Any guidance or reference design checks would be appreciated.

Thanks!

Attachments:

- [Screenshot 2025-06-12 191851.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=257)
- [Screenshot 2025-06-12 191913.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=258)
- [Screenshot 2025-06-13 114428.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=259)
- [Screenshot 2025-06-12 110928.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=260)
- [Screenshot 2025-06-11 200441.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=261)
- [Screenshot 2025-06-11 200502.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=262)
- [Screenshot 2025-06-11 201043.png](https://maker.wiznet.io/forum/getAttach.asp?aidx=263)

## Replies

### Reply 1 by Alan, 2025-06-17

I would appreciate it if you could send the schematic to alan@wiznet.io. Thank you.

---

Source: https://maker.wiznet.io/forum/15766