Integrated vs. Modular RJ45 Connectors – Which Fits Your Ethernet Design?

Introduction: A Crucial Choice in Ethernet Design

RJ45 connectors are fundamental components in Ethernet systems, but engineers often face a design-level decision: Should you use an Integrated RJ45 (MagJack) or a Modular RJ45 (without discrete magnetics)?

This article, tailored for engineers, product designers, and EMS professionals, dives deep into the trade-offs between these two connector architectures—helping you make an informed decision for performance, cost, and manufacturability.

What Is an Integrated RJ45 (MagJack)?

An Integrated RJ45 combines:

• Standard RJ45 interface
• Built-in magnetics (isolation transformers, common-mode chokes)
• Optional LEDs

Advantages:

• Simplified layout — fewer external parts on the PCB
• Smaller footprint — ideal for compact designs
• Faster assembly — reduces BOM count
• Pre-qualified EMI performance

Drawbacks:

•  Limited tuning flexibility
•  Harder to service — the entire module needs replacing
•  Higher cost in low-volume production

What Is a Modular RJ45 (Empty Jack)?

A Modular RJ45 provides just the jack. The magnetics are mounted separately as discrete components.

Advantages:

•  High customization — fine-tune magnetic specs
•  Easier maintenance — replace parts independently
•  Cost-effective for volume production

Drawbacks:

•  Larger PCB area required
•  More complex routing
•  Requires signal integrity expertise

Feature Comparison Table

Design Application Guide

Choose Integrated RJ45 when:

• You need rapid prototyping or fast time-to-market

• Space is constrained (e.g., IoT boards, routers)

• You prefer plug-and-play EMI compliance

Choose Modular RJ45 when:

• EMI tuning is critical (e.g., medical, industrial)
• You build for high-volume production
• Your team has signal integrity design capabilities

Conclusion: Balance Flexibility with Simplicity

The choice between integrated and modular RJ45 designs isn't just about price—it's about control, complexity, and context.

At RJ45-ModularJack.com, we help OEMs and engineers select the best-fit solution from a full range of MagJack and discrete RJ45 options. Whether you're building a compact IoT device or a carrier-grade switch, we support your Ethernet interface design from concept to production.