The following items should be noted when selecting power inductors at design stage.

1. The applying fields should be considered firstly. Power inductors are widely used in the DC-DC conversion circuits, power supply circuits, audio filtering circuits and so on.

2. For DC-DC conversion circuits, the power inductor selected should be determined by the frequency of the applying signal. It is required that the self-resonance frequency should be larger than that of the signal.

3. The inductance selected should fit the design of the circuit. For example, in the DC-DC conversion circuits, power inductor is used to store energy and suppress the ripper. Usually a larger inductance indicates the stronger storage and filtering effect, but at the same time the larger inductance can increase the RDC of the inductor which will decrease energy efficiency and can’t be used for large current application.

4. The power inductor should be selected according to the current of the loop. Two kinds of current should be taken into account. When select the power inductor, the smaller is considered as rated current.

5. The size of power inductor should be selected according to the land pattern and space of the application.

The main electrical parameters of power inductor include L, DCR, saturation current (Isat), heating rating current (Irms), and SRF.

L: L is the nominal inductance of the inductor. Due to the distributing capacitance, the value of L shows frequency dependency. The tolerance of the inductance is commonly classified into M (±20%) and N（±30%）grades.

DCR: DC resistance is the direct-current resistance of the wire between the electrodes.

Saturation Current (Isat): The inductance will decrease under continual current. The Saturation

Current (Isat) is also called DC Superimposition Current and defined as the current at which the inductance drops by 30%.

Heating Rating Current (Irms): The component body temperature will increase under continual current. The Heat Rating Current is defined as the current that causes the component body temperature rise 40℃ from 20℃ ambient.

SRF (Self-resonant Frequency): The SRF is defined as the frequency at which the inductor reaches the resonant state due to the interaction of the inductance and stray capacitance.

S parameters are also called the scattering parameters, which are used for evaluating the performance of DUT reflecting and transmitting signals. The S parameters which contain the amplitude and phase information of the signals are defined as the ratio of two plural.
S parameters usually expressed as: S (output, input)
Output: output port number of DUT
Input: input port number of DUT
For example, S21 means the ratio of the DUT’s output signal in port 2 and the input signal in port 1, and the output signal and input signal are plurals.
First of all, at the high frequency range, S parameters can be got easily and S parameters can correlate with many other familiar parameters such as gain, loss, and reflection coefficient and so on;
Second, the H, Y, or Z parameters can be calculated using the S parameters;
Finally, the S parameters are suitable for all kinds of simulation software.