Part 01
Introduction
When selecting an inductor, if you open the inductor datasheet, you'll find that the rated current is given in two parameters: Isat (saturation current) and Itemp (temperature-rise current). What's the difference between these two currents? How do you verify these two parameters when selecting an inductor?

Part 02
Saturation Current vs. Temperature-Rise Current
TDK datasheets define the rated current as the smaller of the saturation current and the temperature-rise current. This means that the actual current flowing through the inductor cannot exceed the minimum of the saturation current and the temperature-rise current.

Saturation Current: This is defined as the DC current applied when the inductance drops below a specified value as the DC current increases.

It is important to note that the saturation current test conditions and test standards defined in datasheets by different manufacturers may vary. It's important to compare the manufacturer's test conditions with the specified percentage of inductance drop at saturation. Some manufacturers specify the saturation current as a 20% drop in inductance. Others specify it as a 30% drop in inductance. The manufacturer that specifies the saturation current as a 30% drop in inductance will naturally appear to have a higher saturation current, so we must pay attention to the saturation current test conditions and test standards.

There are two types of inductor saturation: hard saturation and soft saturation. Hard saturation occurs when the inductance drops rapidly after saturation, while soft saturation occurs when the inductance drops more slowly after saturation.

Temperature Rise Current: The temperature rise current of an inductor is based on the current flowing through the inductor as the inductor temperature rises. Therefore, this parameter is strongly related to the test conditions. For example, for an inductor rated at 125°C, if the ambient temperature is 85°C, the allowable temperature rise is 40°C. If the ambient temperature is 105°C, the allowable temperature rise is 20°C. When comparing different inductors, don't ignore the corresponding test conditions.

When measuring inductor temperature-rise current, various factors can affect the final test results. For example, PCB trace width: Wider PCB traces provide better heat dissipation, thus affecting the inductor's temperature rise. Narrower traces may limit heat dissipation, causing the inductor's temperature to rise faster. PCB copper foil thickness: Thicker copper foil can carry greater current and dissipate heat more effectively, thus reducing the inductor's temperature rise. Thinner copper foil provides poor heat dissipation and may increase the inductor's temperature rise. Test duration: Longer tests allow the inductor to reach thermal equilibrium, which more accurately reflects the inductor's actual temperature rise. Shorter tests may not allow the inductor's temperature to stabilize sufficiently, resulting in lower test results. Product usage conditions: If the inductor is located near heat-generating components (such as MOSFETs), it will be subject to additional heat, increasing its temperature rise. Air flow and cooling measures in the system design can also affect the inductor's temperature-rise characteristics.

These factors can affect the inductor temperature-rise current test results, so caution should be exercised when referencing temperature-rise current parameters. In practical applications, it is recommended to actually measure the temperature and temperature rise of the inductor to more accurately evaluate its performance in specific applications and make more reliable design choices.