OT: 3.3V Switcher Recommendation

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Looking for a good 3.3V switcher. 300-500mA, low parts count, AVAILABLE... from Digikey or similar, small, SMT, etc.

Any suggestions.

Ttelmah · Guest

Hint. From what?......
Very different parts needed for 3.3v from 100v, versus 3.3v from 5v.

Best Wishes

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Sorry....

From 5-20V Vin.

Also, I from < 1mA to 300-500mA max. (I think I recall from searching data sheets some don't like to operate at the extreme low end?)

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

I'd go to national and follow the simple switcher walk through design.
http://www.national.com/appinfo/power/switcher.html
then cross reference to digikey and check for price/avail qty

..my last design(5v) used a lm2574 and a bobbin inductor.
http://www3.national.com/mpf/LM/LM2574.html
There is also the stand alone software SMS6.3.1.zip
http://www.national.com/appinfo/power/0,1768,383,00.html
look on page for SMS6.3.1.zip

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

The National Simple Switchers were the same components I was thinking of first. If size is important than an alternative to the LM2574 is the Micrel MIC4574 which has the same pinout but a higher frequency of 200kHz making the inductors and capacitors 25% the value as for the LM2574.

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Thanks, I'll look at the Micrel part.

I'm awaiting a return of a board that I just used a switcher for the first time on, a LM2676. (actually two of them, one for 3.3V and another for 5.0V). It's just that I always tiny switchers that I can never decipher the part numbers....

John

Ttelmah · Guest

National also have higher frequency 'variants' in the same family. Their design tool, is a good place to start. The hardest thing for a small system, is getting the inductor 'right'. I think I'd probably suggest the LM3103. I have used a couple of these, on a prototype recently, with surface mount inductors, and the Sanyo 'OSCON' capacitors, to give commendably 'low noise' solutions, in a compact space.

Best Wishes

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

I had the LM3103 suggested using the tool on the NS website but isn't this a new component for which production has to start? It is not in stock with Digikey. Farnell and Future Electronics don't know the component.

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Yes. The 3103 is more of what I was looking for. I have used the WebBench in the past, but usually came up with 'large' solutions.

National links to Digikey as their supplier... but no stock yet as you said. I've requested some samples and will give them a try. The sample page shows full production, 6 week delivery, and NEW.... so, I would expect to see them available on Digikey fairly soon?

Ttelmah · Guest

Yes. The 3103, is available in 'engineering prototype' quantities directly from National, and they have happily commited to delivering the 'production' numbers for the board I was working on, in a few weeks, but it'll take a while to ge 'in stock' at the suppliers I think.
I got the first ones for my job about 6 weeks ago.

Best Wishes