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_Cheap_ buck solution for 9-24V in to 5V out, ~50mA to 1A

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Hi all & greetings from Finland where the snow is finally gone and Miss Spring is in town  ;D.
This is my first post to the forum so i am a noob here, although not otherwise.
The topic really says it, but to fill in some details: I am in the process of designing a small instrumentation system mostly for CNC related stuff, based on Atmel processors and I2C bus. The idea is to distribute the system into measuring / data acquisition units, data processing units and display units. One unit may freely have multiple roles to minimize system cost. The idea is to create units as needed but using a common framework so existing units can be easily mixed and matched. Each individual unit is supposed to be small and low cost.
This brings me to the point: Digikey and Mouser offer heaps of easily applied buck ICs that only need the inductor and a few random components to create a working PSU. This would be ideal only the price in small quantities is, well, disappointing. Paying 4 to 9 $ or € per chip is not in line with the rest of the stuff. A run of the mill ATMega328 for example goes for $ 3 and change. The target is to keep a typical unit definitely below 20 € (we are not competing with the Chinese here) but these chip prices already eat a quarter of that or worse.

So, anyone been in the same situation came up with a brilliant solution?

You must have really low filtering/searching skills.

I bought these from Farnell :


It's less than 1$... 0.45 pounds... even cheaper in quantity.

--- Quote ---Features
•Operation to 40 V Input
•Low Standby Current
•Output Switch Current to 1.5 A
•Output Voltage Adjustable
•Frequency Operation of 150 kHz
•Precision 1.5% Reference
•New Features: Internal Thermal Shutdown with Hysteresis
New Features: Cycle-by-Cycle Current Limiting
•Pb-Free Packages are Available
•Step-Down, Step-Up and Inverting supply applications
•High Power LED Lighting
•Battery Chargers

--- End quote ---

Check the datasheet, it includes everything you need to know including schematics and pcb layout example.

ps. and you'll find it's available from several manufacturers and in different packages, and all should have the same pinout, so you won't be stuck with a one manufacturer solution and possibily of having a hard time getting them :

(there's actually two different chips in the search above, the second is with 33063 in name, which would work as well but has one different pin )


--- Quote from: mariush on April 15, 2012, 02:51:50 pm ---You must have really low filtering/searching skills.
--- End quote ---
Oh, I must? Thanks for the quick eval. I'll have to write that into my resume.
--- Quote ---I bought these from Farnell :
--- End quote ---
Good for you. I don't usually buy from Farnell so much but yes, that chip is available also from DK though not from Mouser. I was looking for higher switching frequency, closer to 1 MHz which i failed to mention in the first post, sorry for that omission. Also, while the specs look like it will work, i want to steer away from the QFN packages if at all possible. If this chip will do 1 amp only in that package i will have think about it.
But yes, it is an answer to the question i asked. Thanks for replying.
It would be even better to find a similar chip switching around 1 MHz to minimize the inductor size.

P.S. Something like this: http://search.digikey.com/us/en/products/AP5100WG-7/AP5100WG-7DICT-ND/2277839. This is still over a buck (pun intended) in small quantities but better than 4 or 9 which was ridiculous.

If you're wanting to keep cost at a minimum and not necessarily space at a minimum then the lower frequency switchers are probably the way to go.  In addition to the cost of the IC, you need to consider the cost of the capacitors.  Some of the higher frequency switchers require crazy-large ceramic capacitors (22uF!?)  Which don't come cheap.

Point taken but at least i have had good luck paralleling 10 uF caps which are readily available at least below 25 V rating.
This exercise is far from completed so everything can be adjusted. Just now my priority seems to be minimizing the inductor size to avoid cumbersome boulders on the tiny PCB, possibly even causing grief during the reflow process (these will be mostly assembled with hobbyist level competence). But even that point is still open to discussion.

Edit: I did a quick naive calculation comparing the prices from DK for 1-10 units. While not scientifically accurate, it shows that the higher frequency solution would be some $ .3 more expensive if using the recommended single 22 uF ceramic output cap. Replacing that with 2 x 10uF caps reduces the price to just under the lower freq solution. The larger inductor is quite a lot more expensive than the small one, as i suspected.
Based on this i opt for the higher freq solution if only to conserve PCB area and minimize the component mass.


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