BROADBAND ACCESS: xDSL, HPN, CMCs # Technical Document: BX2606LNL Common Mode Choke
Manufacturer: PULSE
Component Type: Surface Mount Common Mode Choke (Data Line Filter)
Document Version: 1.0
Date: October 26, 2023
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The BX2606LNL is a surface-mount common mode choke designed primarily for electromagnetic interference (EMI) suppression in differential data lines. Its core function is to attenuate unwanted common mode noise while allowing the intended differential signals to pass with minimal distortion.
* High-Speed Data Line Filtering: It is most commonly deployed in series with differential pair signals, such as USB 2.0 (480 Mbps) , Ethernet (10/100/1000BASE-T) , HDMI , DisplayPort , and LVDS interfaces. The choke suppresses common mode RF noise generated by the data signals themselves or coupled from external sources, preventing both emissions and susceptibility issues.
* Board-Level EMI Mitigation: Placed at cable entry/exit points on a PCB, it acts as a barrier, preventing high-frequency noise from propagating onto the cable (acting as an antenna) or from the cable into the sensitive circuitry.
* Signal Integrity Preservation: By targeting only the common mode component, it minimizes impact on the differential signal integrity, helping to maintain eye diagram compliance for high-speed standards.
### 1.2 Industry Applications
* Consumer Electronics: Smartphones, tablets, laptops, digital TVs, set-top boxes, and gaming consoles, where multiple high-speed data ports coexist in a compact space.
* Computing & Networking: Motherboards, network interface cards (NICs), routers, switches, and servers to ensure compliance with EMI regulations (e.g., FCC, CE) for Ethernet and USB interfaces.
* Automotive Infotainment: In-vehicle systems using USB, LVDS for displays, or Ethernet for camera feeds, where the choke must withstand automotive environmental and reliability standards.
* Industrial Communication Interfaces: Used in PLCs, industrial PCs, and measurement equipment to protect communication ports (RS-485, CAN, Industrial Ethernet) from conducted noise in electrically harsh environments.
### 1.3 Practical Advantages and Limitations
Advantages:
* Effective EMI Suppression: Provides high impedance to common mode currents across a broad frequency range (typically effective from tens of MHz to beyond 1 GHz), significantly reducing radiated emissions.
* Compact SMD Package: The surface-mount design saves board space and is compatible with automated pick-and-place assembly.
* Signal Transparency: Well-designed chokes like the BX2606LNL have minimal impact on differential insertion loss, preserving signal rise times and data integrity.
* Reliability: Constructed with robust materials suitable for reflow soldering and capable of withstanding typical operating temperatures.
Limitations:
* Frequency-Dependent Performance: Impedance is not flat across all frequencies. Designers must ensure the choke's effective frequency range aligns with the noise spectrum of concern.
* Saturation Current: The choke has a rated saturation current. If the differential DC or AC current exceeds this, the inductance drops, degrading filtering performance. This is a critical parameter for power-over-data-line applications like PoE.
* Parasitic Capacitance: Inter-winding capacitance can create an unwanted signal path for high-frequency differential noise, potentially limiting effectiveness at very high frequencies (multi-GHz).
* Impedance Mismatch: Incorrect selection can cause impedance discontinuities on controlled impedance lines (e.g., 90Ω for USB), leading to signal reflections and degradation.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls
