Selecting inductors for BUCK DC/DC regulators

The buck regulators are designed to operate with inductors that have a nominal inductance of 2.2 µH with ± 20% tolerance. To ensure loop stability, do not use inductors with other nominal inductances.

The saturation current of the inductor should be greater than 400 mA. This saturation current requirement should be respected even if the load current range required in the application during design is lower than the maximum load current of the buck regulator. This is because the inductor peak current level is higher than the load current, especially when the buck regulator operates in hysteretic mode.

The choice of inductor has a significant effect on the performance of the buck regulator, especially the efficiency. The choice is typically a compromise between size, performance, and cost. The Direct Current Resistance (DCR) given by the manufacturer is one key indicator of the performance. However, the DCR is not a definitive performance metric as the losses in the inductor also include various frequency-dependent effects like magnetic hysteresis losses, eddy currents, and skin effects.

The following table shows examples of inductor models selected for area, performance, and cost optimized applications.

The following table shows a comparison of buck efficiencies for different inductor manufacturer and models at 3.0 V output voltage. Efficiency numbers were measured by using the nPM1300 Evaluation Kit (EK) with default components and different buck inductors. The input current used in the efficiency calculations includes the whole device battery current.

The following graph shows the typical efficiencies for BUCK1 in PWM mode.