JAJSPW0B June 2023 – June 2024 TPS543B25T
PRODUCTION DATA
To calculate the value of the output inductor, use Equation 16. KIND is a ratio that represents the amount of inductor ripple current relative to the maximum output current. The inductor ripple current is filtered by the output capacitor. Therefore, choosing high inductor ripple currents impacts the selection of the output capacitor because the output capacitor must have a ripple current rating equal to or greater than the inductor ripple current. Choosing small inductor ripple currents can degrade the transient response performance. The inductor ripple, KIND, is normally from 0.1 to 0.4 for the majority of applications giving a peak to peak ripple current range of 2A to 8A. The target IRIPPLE must be 1A or larger.
For this design example, KIND = 0.2 is used and the inductor value is calculated to be 0.183µH. An inductor with an inductance of 0.150µH is selected. Make sure that the RMS (root mean square) current and saturation current ratings of the inductor not be exceeded. The RMS and peak inductor current can be found from Equation 18 and Equation 19. For this design, the RMS inductor current is25.96A, and the peak inductor current is 28.498 A. The chosen inductor is a SLR1050A-151KEC. The inductor has a saturation current rating of 51 A, an RMS current rating of 56.7A, and a typical DC series resistance of 0.39mΩ.
The peak current through the inductor is the inductor ripple current plus the output current. During power up, faults, or transient load conditions, the inductor current can increase above the calculated peak inductor current level calculated in Equation 19. In transient conditions, the inductor current can increase up to the switch current limit of the device. For this reason, the most conservative approach is to specify the current ratings of the inductor based on the switch current limit rather than the steady-state peak inductor current.