---
title: "W5100s Crystal Selection Guide does not match with CL:18pF recommended"
url: "https://maker.wiznet.io/forum/15237"
markdown_url: "https://maker.wiznet.io/forum/15237/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "Miki1"
created: "2024-06-12T15:01:22+09:00"
last_activity: "2024-06-12T15:02:55+09:00"
language: "en"
views: 40
replies: 0
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5100s Crystal Selection Guide does not match with CL:18pF recommended

## Question

Asked by Miki1 on 2024-06-12 in Ethernet Chips.

Following your [crystal selection guide](https://docs.wiznet.io/img/products/w5100s/w5100s_crystal_selection_guide_v100e.pdf):

- Example inappropriate: ESR: 40Ohm C0: 7pF CL: 16pF → GMCRIT: 4.00 GM: 4.04 < 6.9897 **BAD**!

- Example appropriate: ESR: 40Ohm C0: 7pF CL:10pF → GMCRIT: 1.14 GM: 7.39 > 6.9897 **VALID**!

However, I see Crystals with CL: 18pF recommended (the one in the Wiznet Ethernet Hat is X-tal 25MHz,3.2x2.5 SMD, CL=18pF). If I plug the numbers for similar crystals in the formulas above, I get:

- Example X322525MRB4SI: ESR: 50Ohm C0: 3pF CL:18pF → GMCRIT: 2.18 GM: 3.87 < 6.9897 **BAD**!

All crystals I have tried with CL:18pF won’t have the right GM according to your own Crystal Sel Guide.

What are the recommended features of the crystal? Should I stick to the Crystal Selector Guide?

---

Source: https://maker.wiznet.io/forum/15237