Reccomend a high efficiency 5V buck converter IC

[fubar.gr]

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!

[mariush]

See LT1374 if money is not an issue:

SOIC http://www.digikey.com/product-detail/en/LT1374CS8-5%23PBF/LT1374CS8-5%23PBF-ND/888771
TO-220 http://www.digikey.com/product-detail/en/LT1374CT7%23PBF/LT1374CT7%23PBF-ND/889614

Not on Mouser though.

[miguelvp]

Buy one from Ebay?
Not sure about efficency (they quote 92%), but look very versatile and reusable for other projects

http://www.ebay.com/itm/DC-DC-0-30V-8A-Digital-controlled-Step-down-Module-Power-Supply-Constant-CC-CV-/200978486442

Input voltage: 6V ~ 32V
Output voltage: 0 ~ 30V
Output current: 0 ~ 8A
Voltage regulation/display resolution: 0.01 V
Current regulation/display resolution: 0.001 A
The minimum display resolution of power: 0.001 W
The minimum display resolution of capacity: 0.001 AH
Conversion efficiency: up to 92%
The output ripple: <= 50 mV
Working temperature: - 40 C~ + 85 C
Working frequency:150 KHz
Short circuit protection:Constant current
Input reverse connect protection:No, if necessary please install diode
Connection mode: Terminals
Size (mm):80 (long)* 66 (wide) * 33(high)
Weight: 116g

Or 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-/171095601976

Input voltage: 5V~42V
Output voltage: 0~40V
Output current: 0~3A
Voltage control / display resolution: 0.01V
The current regulation / display resolution: 0.001A
Power display resolution: 0.001W
Capacity display resolution: 0.001AH
The highest conversion efficiency: 92%
Output ripple: <= 50mV
Operating temperature: ~+85 C and 40 C
Operating frequency: 150KHz
Short circuit protection: constant current
Input reverse connection protection: No, if necessary please install diode
Connection: connecting terminal
Product size (mm): 66 (long) *50 (W) *21 (high)

Edited for unsuported characters

[rob77]

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.

[rs20]

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.

I really like the TI WEBENCH online tool for 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.

[Precipice]

I really like the TI WEBENCH online tool for 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.

Good 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!

[rs20]

I really like the TI WEBENCH online tool for 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.

Good 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!

I 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.

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!

I 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.

[Precipice]

Hmm - ISO-7637-2 contains quite a lot of voltages, not sure where that 45V came from
Pulse 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 stage

And 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's www.ti.com/lit/an/snva681/snva681.pdf is 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.

[rs20]

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!

...

Agreed 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.

[fubar.gr]

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!

I 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.