Reccomend a high efficiency 5V buck converter IC - Page 1
Forum section: electronics / beginners

author: fubar.gr
author_rank: Unknown
timestamp: August 09, 2014, 11:50:48 am
content: I want to make a super efficient, high output current (3 Amps or more) 5 Volt USB charger, powered from 12V lead acid batteries.I am thinking of using a synchronous, single phase topology with external mosfets.Can you recomend a suitable IC? Cost per unit is not an issue, this will be a one-off project for my personal use.Also it would help if it is available through Mouser.Thanks!

author: mariush
author_rank: Super Contributor
timestamp: August 09, 2014, 12:05:09 pm
content: See LT1374 if money is not an issue:SOIChttp://www.digikey.com/product-detail/en/LT1374CS8-5%23PBF/LT1374CS8-5%23PBF-ND/888771TO-220http://www.digikey.com/product-detail/en/LT1374CT7%23PBF/LT1374CT7%23PBF-ND/889614Not on Mouser though.

author: miguelvp
author_rank: Super Contributor
timestamp: August 09, 2014, 09:30:54 pm
content: Buy one from Ebay?Not sure about efficency (they quote 92%), but look very versatile and reusable for other projectshttp://www.ebay.com/itm/DC-DC-0-30V-8A-Digital-controlled-Step-down-Module-Power-Supply-Constant-CC-CV-/200978486442QuoteOr the cheaper one up to 3A (there some thread in the forum about this one with a video review)http://www.ebay.com/itm/Digital-controlled-Constant-Current-Voltage-LED-Driver-Step-Down-Power-Module-/171095601976QuoteEdited for unsuported characters

author: rob77
author_rank: Super Contributor
timestamp: August 09, 2014, 09:50:48 pm
content: does "powered from lead acid 12V battery" mean that it will be installed in a car ? if yes, then pay attention to input protection (~90V transients..etc...) otherwise you might burn down the car.

author: rs20
author_rank: Super Contributor
timestamp: August 10, 2014, 03:23:13 am
content: Quote from: rob77 on August 09, 2014, 09:50:48 pmI really like theTI WEBENCH online toolfor designing (or at least, finding some good starting part numbers for) this sort of thing. It has an "automotive" checkbox which presumably means "design must tolerate ~90V transients", so you end up only with controller chips that can handle that. Even with the automotive constraint, it's generating designs that produce 5V @ 3.5A @ 97% efficiency, although that's a 26-part design. A 10-part automotive design using the TPS5450-Q1 gives 91% efficency using only 10 parts. Even generates ripple voltages, efficiency curves, thermal measurements... the only thing I don't like about it is that it kinda spoils the thrill of the hunt and makes it all a bit too easy.

author: Precipice
author_rank: Frequent Contributor
timestamp: August 10, 2014, 08:07:50 pm
content: Quote from: rs20 on August 10, 2014, 03:23:13 amGood grief, no. It means that there's an automotive standard papertrail, and probab;y some promises on temperature range, nothing directly to do with being able to handle an automotive power system at all.The first part I picked - TPS62242-Q1 - tops out at 6V!And your faith in Webench is touching. It's been known to generate comedy designs from time to time. It's a good tool, for sure, but still check its working, and then prototype and test!

author: rs20
author_rank: Super Contributor
timestamp: August 11, 2014, 08:31:43 am
content: Quote from: Precipice on August 10, 2014, 08:07:50 pmI stand entirely corrected. I guess I only thought that because last time I clicked that checkbox, I was handed a component that did mention automotive-grade input transients on the datasheet.Here's a component that handles input transients according to "ISO 7637-2:2011 - Road vehicles -- Electrical disturbances":TPS54340-Q1. Apparently ISO 7637 only specifies 45V, so clearly there must be some cars out there that don't adhere to ISO 7637 if 90V is something to be cautious of; or perhaps a TVS or similar is advisable even with one of these parts. Over 90% efficiency most of the way from 0 to 3.5A.Quote from: Precipice on August 10, 2014, 08:07:50 pmI repeat myself, "...or at least, finding some good starting part numbers for...". Never said anything about blind faith or not prototyping, although I do have a 100% success rate (1/1 = 100%) with its design(s). It's an awful lot better than trying to trawl through digikey's or element14's options that have no idea about efficiency! Except of course, the restriction to a single manufacturer.

author: Precipice
author_rank: Frequent Contributor
timestamp: August 11, 2014, 09:27:03 am
content: Hmm - ISO-7637-2 contains quite a lot of voltages, not sure where that 45V came fromPulse 5a (load dump) is a sort of triangular thing, starting at battery voltage, going up to 65-87V in 10ms, then back down, total pulse time 40-400ms, with a source impedance of 0.5-4Ohms. And that's for 12V electrics - 24V is worse!So, basically, your choice for load dump is to either ride it out by having a PSU that's OK with 90V (plus a bit, as headroom is good...) (and you also need to keep working on cold cranking, which involves being powered off 5V for up to 40ms, so a wide working range...) Or you can turn yourself off and hide until it's over (if that's acceptable), or you can try to soak up the load dump pulse with some device that doesn't mind that much energy, over and over again. (That way lies madness, by the way)And then there's the -100V transients, just to really annoy your input stageAnd then there's the fact that individual manufacturers like to raise the bar a bit further, to avoid getting a reputation for dodgy electrics, and it's the OEMs who have to meet this stuff, so who cares...I've not got a multi-manufacturer pulse5 table, but here's a pulse1 one:TI'swww.ti.com/lit/an/snva681/snva681.pdfis probably worth a quick look for how much effort it takes, and I'm not convinced about the bridge stage on the front - that's a bit brave if there are any other ground-relative connections coming out of your box...(Blind faith reference wasn't really aimed at you, more at world in general!)Edit: I've just noticed this is in 'beginners'Much of this stuff can safely be disregarded if you're building something for yourself, and don't mind much if it fails from time to time! OEM standards are painfully high, and a lot of the time defend against unlikely scenarios. The worst case load dump shouldn't happen, and if you're dumb enough to get the jump leads backwards when you jumpstart, then it's your own electronics you'll destroy. It'll be educational. Stick a series diode in, and rate your PSU to survive 45V, and away you go. You might like a fuse, too, since fires in cars are annoying. A software watchdog or other reboot method is handy if you can't reach a reset button or unplug the power. And try to keep the standby current low, nobody likes a flat battery.That TPS54340-Q1 looks fine. (I imagine it's got an identical, apart from the papertrail) non-Q1 version that's cheaper and more available.

author: rs20
author_rank: Super Contributor
timestamp: August 11, 2014, 12:19:57 pm
content: Fubar (OP), is this for an automotive application? If so, read the post above and ignore me! If not, we've gone off on a bit of a tangent!Quote from: Precipice on August 11, 2014, 09:27:03 amAgreed on all points, including the bridge stage being a bad idea. I'd much prefer to use a PMOS connected on the +12V rail analogous to the diagram on page 4 there. You don't blow 1.4V immediately on losses, and you get a true ground.

author: fubar.gr
author_rank: Unknown
timestamp: August 11, 2014, 03:59:28 pm
content: Quote from: rs20 on August 11, 2014, 12:19:57 pmI was thinking of a UPS style battery, hence the 12V lead acid. But it would be nice if it could be powered through a car lighter socket.