---
title: "W5500 TCT Pull-up resistor Wattage"
url: "https://maker.wiznet.io/forum/14909"
markdown_url: "https://maker.wiznet.io/forum/14909/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "dave c99"
created: "2023-05-11T15:16:57+09:00"
last_activity: "2023-05-13T20:25:48+09:00"
language: "en"
views: 181
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 TCT Pull-up resistor Wattage

## Question

Asked by dave c99 on 2023-05-11 in Ethernet Chips.

Hi,

On the w5500_evb the TCT has a 10R pull-up resistor for the center tap of the transformer within the magjack.

What should the minimum power rating be for this resistor as there is no mention of it in the datasheet or EVB schematic.

[![image](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/8/8c6f495c8ffe36c2657af9f44dc1bd8db1e6589f.png) image1075×509 66.2 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/8/8c6f495c8ffe36c2657af9f44dc1bd8db1e6589f.png)

Also what should the power rating be for the 49.9R pull-up resistors for TXP, TXN? if these are driven low for any extended period of time the current would be 3.3/49.9 = 66mA and ~218mW.

Regards,
Dave

## Replies

### Reply 1 by Eugeny, 2023-05-13

Probably [this](https://electronics.stackexchange.com/questions/281913/what-do-pull-up-and-pull-down-resistors-do-in-an-ethernet-phy) and [this](https://www.ti.com/lit/ug/tidu515a/tidu515a.pdf) will help. Second source says **R41: RES, 0 ohm, 5%, 0.1W, 0603** and **R39, R40, R42, R43 RES, 49.9 ohm, 1%, 0.063W, 0402**.

dave_c99:

> if these are driven low for any extended period

I do not think so. There’s very high frequency differential signal in the wires.

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Source: https://maker.wiznet.io/forum/14909