SNVSB28 December 2017 LM25575-Q1
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 continuous conduction mode (CCM), the maximum ripple current IRIPPLE should 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 the following:
This procedure provides a guide to select the value of L1. The nearest standard value (47µH) will be 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 (see Table 1) has a conservative 3.25 Amp saturation current rating. For this manufacturer, the saturation rating is defined as the current necessary for the inductance to reduce by 30%, at 20°C.