I am reading datasheets for 5V boost converters. I want to find one which can supply up to 680mA from a single cell Lipo.
Under electrical characteristics, I am not seeing a parameter such as output current (Iout) but instead seeing a parameter called "Switch Current Limit".
e.g. https://media.digikey.com/pdf/Data%20Sheets/Austriamicrosystems%20PDFs/AS1325.pdf
Is this the right parameter to use ?
Thanks
Read the datasheet - it very clearly states the max output current right at the start.
Hi MarkT,
I'm afraid you are quite mistaken. The numbers at the start are at input voltage of 2V which is at the lower end of the input range. And contrary to your claim, nowhere does it say "max" output current.
But thanks to the advice of more thorough and helpful members of the community, I now know to look at the graphs later in the datasheet which indicate that the max output current in the lipo range is between 450mA and 550mA for a Vout of 5V.
This is typical of DC-DC converter IC specs - you have to go to the graphs to figure out what you want to know, the headline specs are often misleading. On one of my first projects using them, I bought several different ones intending to try them all out and compare - only to realize once I had them that I'd misunderstood the datasheets and none of them were even close to suitable.
As an aside - are you making your own PCB? DC-DC converters are highly sensitive to layout. I've done it with small breakout boards, with the supporting components located as close as possible to the chip, including minimizing the length of the leads, etc. It worked okay, though probably not to full spec of boost converter IC. Forget about using breadboard for any of the key connections (between inductor, chip and capacitors) - it won't work.
If you're not making a custom PCB for it, I would strongly suggest that you just buy a pre-assembled DC-DC converter module from pololu (excellent selection), adafruit, or ebay (ebay is much cheaper than the other two, but the performance and efficiency is generally worse).
The main limitation of boost converters is the maximum switcher current , and that will determine the maximum output current based on the voltage conversion ratio.
The maximum output current is not normaly specified as its variable.
ainumpudi:
Hi MarkT,I'm afraid you are quite mistaken. The numbers at the start are at input voltage of 2V which is at the lower end of the input range. And contrary to your claim, nowhere does it say "max" output current.
But thanks to the advice of more thorough and helpful members of the community, I now know to look at the graphs later in the datasheet which indicate that the max output current in the lipo range is between 450mA and 550mA for a Vout of 5V.
They will be normal operating current maximums, not absolute max (which you never want to reach anyway).
If they advertise this at the head of the datasheet, that's the marketing bit, they are showing the chip in
its best light normally, for the expected use-cases.
Yes at 3.7V in and 5V out you can get to 450mA or so max, but that's based on a "typical" graph, not
a worst-case value, so you can pretty much ignore that. Anyway nothing about this chip suggests
it can ever handle 680mA output so its striked out from the get-go