Buck Converter Inductor choice for both heavy and light load

Hi everyone,

I have difficulty in selecting a proper inductor for a buck converter with TPS5430(Datasheet). The schematic I use is similar to the examples in the datasheet. After doing some research, I learned that a lower current load would prefer a higher inductance value whereas a higher current load would prefer a lower inductance value. Also, a bigger inductance value is generally better if size and cost are not in consideration. However, in my application, the load varies from 0.2A to 3A.

For 10v to 28v Vin, and 5v Vout, the TI WEBENCH power designer suggests:

• if Iout Max 3A: 15uH (this seems to fit my requirements)
• if Iout Max 1A: 47uH
• if Iout Max 0.2A: 100uH

In this case, what inductor size should I use to support 0.2A-3A? Would a 15uH, 3.3A inductor work? What would be the consequence of the load remains light(<0.5A) for most of the time?

Ian

The efficiency graph in the lower left of the datasheet shows that the 500kHz 3A max design works just fine with good efficiency down to 500mA. So the 15uH iron core inductor will work fine. The design is in the datasheet in section 8.2.1.