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Cx Family Common Mode Chokes

0402CT Low Profile Chip Inductors

XAL7050 High-inductance Shielded Power Inductors

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For example, many Coilcraft products are designed for an 85°C ambient environment and a 40°C temperature rise implying a maximum part temperature of +125°C. In general, the maximum allowed part temperature is the maximum ambient temperature plus temperature rise. If the losses that result in the maximum allowed part temperature meet the power budget limits, the component is considered acceptable for the application.

The temperature rise created by core and winding losses is related to the thermal dissipation characteristics of the specific component. For example, 100 mW of loss might create a temperature rise of 40°C in one inductor but may result in only a 30°C rise in another inductor that has better thermal dissipation (thermal resistance) properties.

Thermal resistance is not specified for Coilcraft inductors or transformers because they are mostly open frame style and not solid, homogenous bodies like molded IC packages. These body styles have a variety of thermal flow paths and multiple heat sources (winding and core) as opposed to an IC that may generate heat in a specific junction and conduct heat consistently throughout the solid body.

From the datasheet specifications for DCR and Irms, an approximate thermal resistance (Rth) can calculated. Dividing the temperature rise due to Irms current (e.g. 40°C rise) by the power required to generate that rise (Power = DCR × Irms

where DCR is in Ohms and Irms is in Amps.

Once a thermal resistance is calculated for a specific component, it is assumed that it is a fixed property of the materials and construction and does not vary at other operating conditions (temperature, current, frequency, etc.). Under this assumption, the temperature rise resulting from any specific power dissipation can be estimated from:

where:

Trise is the temperature rise

Rth is the thermal resistance in °C/W and

P is the dissipated power in Watts

The Irms rating is the effective DC (or low-frequency AC) current that causes the specified temperature rise. The actual temperature rise will be higher when core and winding losses are involved. Lower current must be applied as operation approaches the maximum ambient temperature rating. At lower ambient temperatures, the allowable temperature rise is that which results in the maximum allowed (ambient + temperature rise) part temperature. Core and winding losses depend on current and frequency, and the specific component material and construction. Therefore, current derating (based on temperature rise) depends on the specific losses resulting from the amplitude and frequency of the AC ripple current.

Core and winding losses, and an estimate of the resulting temperature rise, can be calculated for Coilcraft’s power inductors using the web tool at this link: http://www.coilcraft.com/apps/loss/loss_1.cfm

Frequency-dependent small signal losses for our RF chip and air core spring inductors can be estimated based on the effective series resistance (ESR).

The ESR of our RF chip and air core spring inductors can be found using the graphing web tool at this link: http://www.coilcraft.com/apps/lqz/lqz.cfm

Given the ESR at a specific frequency and the datasheet ratings, the maximum current the inductor can theoretically handle at that frequency (at maximum ambient temperature) can be estimated.

Example: An 1812CS-102XJL (1 µH) chip inductor has an Irms rating of 480 mA and a DCR maximum rating of 1.2 Ohms. The Irms rating corresponds to a 15°C temperature rise from ambient. The maximum allowed ambient temperature is 125°C, so the 15°C temperature rise allows for a maximum part temperature of ~140°C (125 + 15).

To estimate the power capability at maximum ambient temperature, calculate:

Note that this assumes the nominal DCR to be 80% of the maximum specification. So, approximately 221 mW of power will cause the temperature of this inductor to rise ~15°C.

At RF frequencies, the ESR may be much higher than the DCR, therefore the amount of current that causes the same temperature rise will be significantly reduced. For example, if the RF signal is 100 MHz, the ESR of the 1812CS inductor in the example above is 8.14 Ohms (almost seven times the DC resistance) so the Irms AC current that corresponds to the same power (and thus temperature rise) is only 161 mA versus the 480 mA Irms rating.

If the application ambient temperature maximum is lower than the component data sheet maximum ambient temperature rating, it may be possible to operate at higher than rated current. Again, as long as the total (application maximum ambient + application component temperature rise) component temperature does not exceed the data sheet total (maximum ambient + component temperature rise due to Irms current) the part can be operated within safe limits.

To estimate the temperature rise due to current, use the power and thermal resistance calculations as described in the section above.

References: Current and Temperature Ratings, Coilcraft, Inc., Document 361, October 22, 2008

- Assistance with Safety Agency Approvals
- Basics of Inductor Selection (from Electronic Design magazine)
- Calibration, Compensation, and Correlation
- Current and Temperature Ratings
- Getting Started: An Introduction to Inductor Specifications
- Hipot Testing of Magnetic Components
- Measuring Self Resonant Frequency
- Operating Voltage for Inductors
- Selecting Current Sensors and Transformers
- Simulation Model Considerations: Part I
- Simulation Model Considerations: Part II
- S-parameters for High-frequency Circuit Simulations
- Testing Inductors at Application Frequencies
- Working Voltage Ratings Applied to Inductors

- PCB Washing and Coilcraft Parts
- Selecting Flux for Soldering Coilcraft Components
- Soldering Surface Mount Components

- Broadband Chokes for Bias Tee Applications
- Inductors as RF Chokes
- Key Parameters for Selecting RF Inductors

- Beyond the Data Sheet: The Need for Smarter Power Inductor Specification Tools
- Choosing Inductors for Energy Efficient Power Applications
- Current Sense Transformers for Switched-mode Power Supplies
- Determining Inductor Power Losses
- Ferrite Vs Pressed Powder-core Inductors
- Forward or Flyback? Which is Better?
- Notes on Thermal Aging in Inductor Cores
- Selecting Coupled Inductors for SEPIC Applications
- Selecting Inductors to Drive LEDs
- Selecting the Best Inductor for Your DC-DC Converter
- Structured Design of Switching Power Transformers
- Transformers for SiC FETs

- Coilcraft LC Filter Reference Design
- Common Mode Filter Design Guide
- Common Mode Filter Inductor Analysis
- Data Line Filtering
- Fundamentals of Electromagnetic Compliance
- Passive LC Filter Design and Analysis
- Selecting Common Mode Filter Chokes for High Speed Data Interfaces

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- Choosing Power Inductors for LiDAR Systems
- Coilcraft Conical Inductors
- Designing a 9th Order Elliptical Filter for MoCA® Applications
- Measuring Sensitivity of Transponder Coils
- Power-handling Capabilities of Inductors
- Signal Transformer Application
- Transponder Coils in an RFID System
- Using Baluns and RF Components for Impedance Matching
- Using Standard Transformers in Multiple Applications