Customer looking at efficiency curves in Figure4 - the curve stops at about 300mA load, when Vin=2V7. Why is this and what is the efficiency at 400mA?
Also, Figure 20 - what is the device's switching frequency when output is 400mA?
Does the curve in Figure4 stop at 300mA because the current limit has been reached because the ripple gets too large due to decreased switching frequency?
The reason the graphs stop around 300 mA is because operating above this would be outside of the recommended operating conditions, listed on page 3. I believe the footnote actually give a fairly clear reason for this limit--thermal. Without a thermal pad, the device will get very hot, especially at elevated temperatures. With lower Vins, the Rdson is at its highest, leading to higher conduction losses which are dominant at heavy loads.
We recommend using different devices, such as TPS62260 or TPS62080 for higher load currents at low Vins.
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