Balun coil< SMD Type: CBM Series> # CBM33 Series Common-Mode Choke Coils Technical Documentation
*Manufacturer: SUMIDA*
## 1. Application Scenarios
### Typical Use Cases
The CBM33 series common-mode choke coils are primarily employed for electromagnetic interference (EMI) suppression in various electronic circuits. These components effectively attenuate common-mode noise while allowing differential signals to pass with minimal attenuation. Typical applications include:
- Power Supply Filtering : Integrated into switch-mode power supply inputs to suppress conducted EMI and meet regulatory requirements (FCC Part 15, CISPR 32)
- Signal Line Filtering : Used in high-speed data lines (USB, Ethernet, HDMI) to reduce common-mode noise that could degrade signal integrity
- Motor Drive Circuits : Suppress electromagnetic noise generated by brushless DC motors and motor drivers
- LED Lighting Systems : Filter high-frequency switching noise in LED driver circuits
### Industry Applications
Automotive Electronics :
- Infotainment systems
- ADAS (Advanced Driver Assistance Systems)
- Battery management systems
- The CBM33's automotive-grade variants operate reliably in temperature ranges from -40°C to +125°C, meeting AEC-Q200 requirements.
Consumer Electronics :
- Smartphone charging circuits
- Television power supplies
- Gaming console power management
- Audio/video equipment
Industrial Automation :
- PLC (Programmable Logic Controller) I/O modules
- Industrial communication interfaces
- Power conversion systems
### Practical Advantages and Limitations
Advantages :
- High common-mode impedance (typically 100Ω to 1kΩ at 100MHz)
- Excellent saturation current characteristics
- Compact SMD package (3.3mm × 3.3mm footprint)
- Wide operating temperature range (-40°C to +125°C)
- RoHS compliant and halogen-free construction
Limitations :
- Limited to common-mode noise suppression (ineffective for differential noise)
- Frequency-dependent performance characteristics
- Physical size constraints limit maximum current handling capacity
- Requires careful PCB layout for optimal performance
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Current Rating Selection
- Problem : Selecting a choke with insufficient saturation current leads to performance degradation under load
- Solution : Always verify the RMS current and peak current requirements, adding 20-30% safety margin
Pitfall 2: Frequency Response Mismatch
- Problem : Choosing a choke with impedance peak outside the target noise frequency band
- Solution : Analyze the noise spectrum and select a choke with maximum impedance at the problematic frequencies
Pitfall 3: Thermal Management Issues
- Problem : Overheating due to high RMS currents or poor thermal design
- Solution : Ensure adequate copper area around pads for heat dissipation and consider derating at elevated temperatures
### Compatibility Issues with Other Components
Power Supply ICs :
- Ensure the choke's DC resistance doesn't cause excessive voltage drop
- Verify compatibility with switching frequencies (typically 100kHz to 2MHz)
Digital ICs :
- Check that the choke's self-resonant frequency doesn't interfere with signal integrity
- Ensure adequate bandwidth for high-speed data lines
Capacitors in Filter Networks :
- Properly match choke impedance with X/Y capacitors in π-filters
- Consider the impact on filter corner frequency and stability
### PCB Layout Recommendations
Placement :
- Position the choke as close as possible to the noise source
- Maintain minimum distance from heat-generating components
- Ensure symmetrical placement for balanced common-mode rejection
Routing :
- Keep differential traces parallel and of equal length
- Minimize loop areas to reduce differential-to-common-mode conversion
- Use ground planes beneath the choke for improved performance
Thermal Management :
- Provide adequate copper pour connected
