Ultra-low power switching boost converter - in a DIP

LTC3803 is a nice little boost converter in a leaded package. Supply current is a little higher, and it needs an external fet, 2N7002 maybe.

Or you could design your own circuit.

Various outfits sell SMT breakout boards fairly cheap. I like the Bellin Dynamic Systems ones, available from Newark. You might have to use paste and a heat gun to get it onto the breakout, but after that it's plain sailing.

Cheers

Phil Hobbs

Data sheet says it's optimized for high input voltages. What low voltages have you used it for, and how did it cope?

Clifford Heath.

upside down. put a 1mm wire across the centre pad and solder the ends down, use finer wires for the other pads.

George H.

Do they make QFN adapters? There's a post-it on my door that says NO QFNS. Everybody hates them.

I would never have thought of that, I'm ashamed to say. Thanks very much.

The problem with all those that I've found so far is that they don't provide for the thermal/ground pad underneath the center of the chip. But I'm not sure I really need that. The data sheet is pretty clear in saying that that pad "must" be soldered to the PC board, but if I'm only looking at a few milliamps of output current, I'm not sure that's really necessary.

I've been watching videos on Youtube of guys using soldering paste and heat guns to do actual reflow work. But I still wonder about the themal pad underneath - I guess it would reflow there in a legit oven, but not sure about a heat gun.

Jason Betts says mount it upside down. and solder thin wires to the pins, and a thicker wire across the thermal pad. I'm liking that idea more and more, subject to it broadcasting too much noise.

Anyway, thank very much for the replies and suggestions.

Yeah I've done the upside down "trick" to the thermal pad with some copper tape. (onto copper clad.) I've also made a big hole in the pcb and soldered to the pad from the bottom. (with an iron)... hole big enough for a solder iron tip to fit through.

George H.

Yes it should be doable though not much fun. Similar to one of my masterpieces

I don't know about this chip, but some use the thermal pad as an electrical connection. I've seen one that uses it as the *only* ground pin.

Yeah, those who aren't very good at manufacturing don't like them. That's why I'd never consider building my own assembly line. Contract manufacturers don't seem to have any problem with them... or the big builders who have to save every penny they can, like in cell phones, etc. QFNs are very common and very useful.

That's your output voltage. What's the lowest input voltage you've used it with?

True, but we can assume less than 24 is likely.

I love QFNs! Good thermal performance, smaller than QFP and more reliable, and impossible to short between pins (which was interesting as I had some rework recently where I had to add a short between pins..).

What I don't like is the MCUs that invariably have pins coming out every which way. MSP430s do it. STM32s do it. The hell is up with that? Why would 32 bits of bus end up jumled!? It literally takes as much PCB space to rout such a QFN, as the QFP takes up! (The QFP would still be worse, though routing underneath is easier at least, not needing to allow for a ground pad.)

Tim

Also, the RF emissions should be lower as there should be less ground bounce.

John

For the most part, QFNs are just QFP packages with the leads cut off. I suppose there are some smaller pin count packages which have not corresponding QFPs and they can be uniquely small. But a 100 pin QFN has the same body size as a 100 pin QFP. I have seen QFNs with multiple rows of pads, but technically, I believe they become LGAs, no?

Not sure what you mean, "every which way". Are you talking about pads on all surfaces like a porcupine? The QFN parts I have seen were still all planer.

I suspect he means that pins that would naturally be grouped together, like a data bus are spread out in a seemly random fashion, so to route a memory bus you need to get to all four sides of the chip and swap the order on the way

-Lasse

Why would that be any different from any other package? The order of pins on the package is usually the same or close to the order of pins on the die.