The datasheet for this device says to “Choose the inductor ripple current to be 30% of the maximum load current.” It does not say where this 30% value comes from or the impact to the operation of the circuit when the ripple current varies from this value. Please explain the ramifications if 30% is not used.
If the inductor gets much bigger so say under 20% current ripple, the duty cycle tends to get jittery. As the slope of the inductor current is low, small changes in the value of the turn off current become large changes in duty cycle. If you don’t mind jitter, I don’t think any harm is done. Bigger inductors tend to be physically larger and more expensive. If the inductor gets smaller say 70% current ripple, the peak to average current is going up and so since there is a fixed maximum peak current the power capability is going down. If you don’t need the full 2 amps that likely isn’t a problem either.
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Hello @wnm
In addition to Jshannon’s response, the inductor current ripple is also a key factor in determining the conduction mode of the converter. If choosing a higher % current ripple, it might affect its performance if the inductor operates out of its peak current range and there’s a chance that your inductor might saturate as well.
Hope this helps.
Best,
Saquib
Thank you for the quick replies. In my design I’m looking at 37.1% ripple for an output current of 1.4A @ 3.45v and a supply voltage of 11.8v . The inductor is 4.7uH with a 5.3A rated current so I should not be in any trouble. I just wanted to be sure that I wasn’t missing anything given that there was no rational given for the datasheet’s rather inflexible “use 30%” statement.