SNOSB23F October 2008 – July 2019 LM5575-Q1
PRODUCTION DATA.
The inductor value is determined based on the operating frequency, load current, ripple current, and the minimum and maximum input voltage (VIN(min), VIN(max)).
To keep the circuit in CCM, the maximum ripple current IRIPPLE must be less than twice the minimum load current, or 0.4 Ap-p. Using this value of ripple current, the value of inductor (L1) is calculated using Equation 8 and Equation 9:
This procedure provides a guide to select the value of L1. The nearest standard value (47 µH) is used. L1 must be rated for the peak current (IPK+) to prevent saturation. During normal loading conditions, the peak current occurs at maximum load current plus maximum ripple. During an overload condition, the peak current is limited to 2.1 A nominal (2.5 A maximum). The selected inductor has a conservative 3.25-Amp saturation current rating. The saturation rating is defined by inductor manufacturers as the current necessary for the inductance to reduce by 30%, at 20°C.