When selecting an inductor, several attributes must be examined to find the right part for the application. First, the inductance value should be selected. The BQ2416xx is designed to work with 1.5-µH to 2.2-µH inductors. The chosen value will have an effect on efficiency and package size. Due to the smaller current ripple, some efficiency gain is reached using the 2.2-µH inductor, however, due to the physical size of the inductor, this may not be a viable option. The 1.5-µH inductor provides a good tradeoff between size and efficiency.

Once the inductance has been selected, the peak current must be calculated in order to choose the current rating of the inductor. Use Equation 5 to calculate the peak current.

Equation 5.

The inductor selected must have a saturation current rating greater than or equal to the calculated I_PEAK. Due to the high currents possible with the BQ2416xx, a thermal analysis must also be done for the inductor. Many inductors have a 40°C temperature-rise rating. The DC component of the current can cause a 40°C temperature rise above the ambient temperature in the inductor. For this analysis, the typical load current may be used adjusted for the duty cycle of the load transients. For example, if the application requires a 1.5-A DC load with peaks at 2.5 A 20% of the time, a Δ40°C temperature rise current must be greater than 1.7 A:

Equation 6.

The BQ2416xx provides internal loop compensation. Using this scheme, the BQ2416xx is stable with 10 µF to 200 µF of local capacitance on the SYS output. The capacitance on the SYS rail can be higher if distributed amongst the rail. To reduce the output voltage ripple, a ceramic capacitor with the capacitance between 10 µF and 47 µF is recommended for local bypass to SYS. A 47-µF bypass capacitor is recommended for optimal transient response.