9.2.2.1 Inductor Selection

A boost converter normally requires two main passive components for storing energy during the conversion, an inductor and an output capacitor are required. It is advisable to select an inductor with a saturation current rating higher than the possible peak current flowing through the power switches.

The inductor peak current varies as a function of the load, the input and output voltages and can be estimated using Equation 4.

Equation 4.

Selecting an inductor with insufficient saturation performance can lead to excessive peak current in the converter. This could eventually harm the device and reduce it's reliability.

When selecting the inductor, as well as the inductance, parameters of importance are: maximum current rating, series resistance, and operating temperature. The inductor DC current rating should be greater (by some margin) than the maximum input average current, refer to Equation 5 and Current Limit Operation section for more details.

Equation 5.

The TPS61256A series of step-up converters have been optimized to operate with a effective inductance in the range of 0.7µH to 2.9µH and with output capacitors in the range of 22µF to 47µF. The internal compensation is optimized for an output filter of L = 1µH and C_O = 22µF. Larger or smaller inductor values can be used to optimize the performance of the device for specific operating conditions. For more details, see the Checking Loop Stability section.