JAJSDX2C September 2017 – October 2021 LM5150-Q1
PRODUCTION DATA
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When selecting the inductor, consider three key parameters: inductor current ripple ratio (RR), falling slope of the inductor current, and RHP zero frequency (FRHP).
Inductor current ripple ratio is selected to have a balance between core loss and copper loss. The falling slope of the inductor current must be low enough to prevent subharmonic oscillation at high duty cycle (additional RSL resistor is required if not). Higher FRHP (= lower inductance) allows a higher crossover frequency and is always preferred when using a smaller value output capacitor.
The inductance value can be selected to set the inductor current ripple between 30% and 70% of the average inductor current as a good compromise between RR, FRHP, and inductor falling slope. In this example, 60% ripple ratio (RR = 0.6) is selected as the maximum inductor current ripple ratio (the inductor current ripple ratio is the biggest when D = 0.33). The target inductance value is calculated as follows:
If the target inductance is smaller than the value calculated using Equation 21, consider adding the slope compensation resistor (RSL), as mentioned in Section 9.2.2.6, or select a smaller RR and recalculate the inductance using Equation 20.
A standard value of 1.5 µH is chosen for LM. The required inductor saturation current rating is estimated after selecting RS and RSL.