I want to use a boost converter which will convert 3.6v@3.4A to 12v@1A i.e. 12Watts. I have collected different IC's datasheets by looking at the "Efficiency vs Output current" graph.
I am confused with "Switching current limit". e.g I am looking at the datasheet of LM2700 in which the "Efficiency VS Iout" graph shows approx ~85% @ 12|1amp (Vin 3.3v) which is acceptable for my application (screenshot is attached here).
But when I viewed the "Switch Current Limit VS VIN" curve; it shows that when Vout=12v, switching current is less than 2A (screen shot is attached here).
And my switching current is about >3.4A (i.e. >12W/3.6v). So this will not work for me? But how did they provide the "Efficiency VS Iout" curve at 12v@1A (Vin=3.3v) in the first place when this regulator isn't able to handle that much "switching current"? Maybe I am missing something.
I would be glad if someone can clear this point to me. Thank you.
Best Answer
You need to revise your expectations because you'll be lucky to get consistently over 90% from a boost converter.
Peak switching currents and average load currents are not the same. The graph with a 3.3 volt supply and a 12 volt output is for a maximum load current of 500 mA. The graph's X axis ends at 1 amp and maybe you have misinterpreted this?
So, with a 6 watt output and a 3.3 volt input supply, the average current taken from the 3.3 volt supply is 1.82 amps (100% efficient) which rises to about 2.14 amps at 85% efficiency and broadly in-line with your 2nd graph.
To get 12 volts and 1 amp from a 3.6 volt supply you should consider either of these (or similar ones from other suppliers): -