Common Mode Choke Coil Wire Wound Type DLW21S Series (0805 Size) # Technical Documentation: DLW21SR670HQ2L Common Mode Choke
*Manufacturer: MURATA*
## 1. Application Scenarios
### Typical Use Cases
The DLW21SR670HQ2L is a surface-mount common mode choke designed for electromagnetic interference (EMI) suppression in high-frequency digital circuits. Typical applications include:
- Differential signal line filtering in high-speed data interfaces (USB 2.0/3.0, HDMI, Ethernet)
- Power supply noise suppression in switch-mode power supplies and DC-DC converters
- Common mode noise attenuation in motor drive circuits and industrial control systems
- Signal integrity enhancement in high-speed digital communication systems
### Industry Applications
- Consumer Electronics : Smartphones, tablets, laptops, gaming consoles
- Telecommunications : Network equipment, routers, base stations
- Automotive Electronics : Infotainment systems, ADAS, power management
- Industrial Automation : PLCs, motor drives, sensor interfaces
- Medical Devices : Patient monitoring equipment, diagnostic instruments
### Practical Advantages and Limitations
Advantages:
- High common mode impedance (67Ω @ 100MHz) provides excellent noise suppression
- Compact 0805 package (2.0×1.25×1.25mm) saves PCB space
- High current rating (200mA) suitable for power line applications
- Excellent frequency response up to 1GHz
- AEC-Q200 qualified for automotive applications
Limitations:
- Limited to common mode noise - less effective for differential mode noise
- Saturation current constraints may limit high-current applications
- Temperature-dependent performance requires thermal management in harsh environments
- Limited to surface-mount applications - not suitable for through-hole designs
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Incorrect Placement
- Problem : Placing choke too far from noise source reduces effectiveness
- Solution : Position choke as close as possible to noise-generating components or connectors
Pitfall 2: Inadequate Current Rating
- Problem : Operating near maximum current rating causes saturation and performance degradation
- Solution : Derate current usage to 70-80% of maximum rating and consider thermal effects
Pitfall 3: Poor Grounding
- Problem : Inadequate ground connections reduce common mode noise rejection
- Solution : Ensure solid ground plane beneath choke and minimize ground return paths
### Compatibility Issues with Other Components
Capacitor Interactions:
- Decoupling capacitors should be placed before and after the choke for optimal filtering
- Avoid resonant circuits formed by choke inductance and parasitic capacitances
IC Compatibility:
- High-speed ICs may require additional differential mode filtering
- Sensitive analog circuits may need additional shielding despite choke implementation
Connector Considerations:
- Board-to-board connectors should have the choke placed immediately before the connector
- Cable interfaces require choke placement at the cable entry point
### PCB Layout Recommendations
Placement Strategy:
```
[Noise Source] → [DLW21SR670HQ2L] → [Sensitive Circuit/Connector]
```
- Maintain minimum distance between choke and noise source/sensitive components
- Position choke in series with signal/power lines requiring common mode filtering
Routing Guidelines:
- Keep differential pairs balanced and symmetrical through the choke
- Maintain consistent trace width and spacing through the component
- Avoid vias between choke and connectors to minimize impedance discontinuities
Grounding Requirements:
- Provide solid ground plane beneath the component
- Ensure multiple ground vias
