This document provides guidelines and recommendations for designing a robust PCB and reducing system debug time for the KSZ8841/42 family of Ethernet controllers in LAN applications. It covers topics such as PCB layout and layer strategy, power supply considerations and decoupling, Ethernet front end design and ESD protection, signal integrity issues, and hands-on debug techniques.
The note explains the key PCB design considerations for high‑speed Ethernet controllers, covering layer strategy, power‑supply decoupling, signal‑integrity, and ESD protection. It also offers hands‑on debugging steps and reference waveforms for the KSZ8841/42 family.
Key recommendations include using a minimum of four PCB layers, controlling trace impedances, placing decoupling capacitors close to power pins, routing differential pairs with matched lengths, and adding proper ESD protection components.
| Recommended PCB layers | At least 4‑layer |
|---|---|
| Microstrip propagation delay | 145 pS per inch |
| Stripline propagation delay | 180 pS per inch |
| Core voltage VDDCO | 1.2 V |
| ISET reference voltage | 500 mV |
| Clock tolerance | +50 ppm |
| Differential pair trace width/spacing | 5 mil width and 5 mil spacing |
Micrel recommends using at least a four‑layer PCB.
The VDDCO pin provides a 1.2 V digital core voltage.
Use 5 mil trace widths with 5 mil spacing for differential pairs.
The clock must be within ±50 ppm.