IC: Modular USB Power Supply
Mar 28, 2009 at 12:03 AM Post #47 of 66
This is where it's at now; there's no nice way (that I can see) to have the USB connectors coincident and route them cleanly. I'm reconsidering having double capacitors on the outputs; it seems like there's less benefit there than on the input side.

Still, with the dual SMD capacitors, the best I can manage with regards through-hole caps is this:

mups-eagle-101.png


Removing the extra SMD caps allows me to move the film caps around enough that you should be able to squeeze in 6mm wide box caps in each position:

mups-eagle-101c.png


As you can see, there's not a lot of real estate to play around with...

Thoughts? I'm leaning towards the lower design, because it better accommodates the "boutique cap" crowd...
 
Mar 28, 2009 at 1:23 AM Post #48 of 66
I prefer the original design you started with, small simple and does the job.

Will there be room for the battery snap if the board is the same length as a 9V battery?

And is the mounting hole still in the right position, or has it moved to far back?
 
Mar 28, 2009 at 5:28 AM Post #49 of 66
The mounting hole is still in the right spot, and there's still plenty of clearance to do the battery-snap thing. Basically, nothing from the IC and "right" has changed from the prototype I've tested, and which others will be playing with shortly. Everything left of there got a bit more crowded, either to accommodate the "I want through-hole caps" crowd, or the "omg a cheap flimsy mini-b connector would be teh roxorz" camp, or because - in the case of the extra SMD caps - it might improve measurable performance, and basically adds nothing to the overall cost of ownership.

So, yeah, to recap:
  1. Still fits a Mini3, and mates nicely with its "ribbon" hole;
  2. Still accommodates single or dual-output 1W or 2W TI isolated DC-DC converter chips, through-hole or SMD;
  3. Still fits wherever a 9V battery goes, with room to connect it with battery snaps;
  4. Still will cost around $25 USD to build;
  5. Still supports an LED powered either off the USB 5V supply or the isolated output of the converter IC, or both;
  6. Still supports the recommended high-quality 1206 SMD capacitors;
  7. Still supports high-quality, rugged, easy-to-solder B-type USB connector;
  8. Still supports modular use in a variety of installations through the use of small Molex-style connectors for input and outputs;

...and now, in theory, could:
  1. ...provide the option of using low-profile, through-hole mini-B USB connector;
  2. ...allow the use of small film, tantalum, or ceramic through-hole capacitors with 5mm lead spacing;
  3. ...allow the use of paralleled 1206-size SMD capacitors on the input, providing theoretical better measurable (but probably not audible) performance;

...at the expense of a less-elegant layout and more confusing assembly.
 
Mar 28, 2009 at 1:49 PM Post #50 of 66
I wonder if this will even fit inside a 9V battery case. I'm thinking of that CMoy that fit into the 9V battery and snapped with an actual 9V for power. Was it Apheared that made it? I think it would be pretty leet since it's already pretty much the size of a 9V it'd be cool to fit it inside of one. It'd definitely be a challenge though, but it would be pretty flippin' sweet. Of course, it'll have a USB connector on the other end...

I'm not suggesting more work for you to do, Nemo. I'm just thinking of the possibilities. Using the DCP020509 at 82% efficiency at full load, you should get 182mA max output current. The Maha battery safety sheet says it can combust if you open it up, so maybe that brand of battery would be a bad candidate. It would work in applications like the PIMETA as well. PPAS? And I guess maybe for legacy portable designs like the CMoy, A47. Maybe even with commercial portable amps like the Graham Slee Voyager. Basically anything requiring a 9V battery, nothing keeping us just to audio too. Call me a dreamer.
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Edit: Also, how sure are you of stacking chips on top of each other? The USB 2.0 spec gives 2.5W although you can probably draw a lot more than that, but have you read TI's application note SBAA035A? I'm not sure of when anyone will be drawing more than 2W, so I don't think there'd be a case in which one will be stacking chips as you describe except for if they wanted 2W at 12V. Perhaps it will work by just stacking the chips, but the application note never mentions anything like that.
 
Mar 28, 2009 at 5:57 PM Post #51 of 66
Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif
I wonder if this will even fit inside a 9V battery case. I'm thinking of that CMoy that fit into the 9V battery and snapped with an actual 9V for power. Was it Apheared that made it? I think it would be pretty leet since it's already pretty much the size of a 9V it'd be cool to fit it inside of one. It'd definitely be a challenge though, but it would be pretty flippin' sweet. Of course, it'll have a USB connector on the other end...

I'm not suggesting more work for you to do, Nemo. I'm just thinking of the possibilities.


It is for all practical purposes as small as it can get and still support the full-sized b connector. That said, it may not literally fit inside a 9V battery shell, but if someone got creative with epoxy resin it could certainly be cast into something with the dimensions and appearance of a 9V battery, albeit with a USB connector on the bottom.
smily_headphones1.gif


But, yeah; it'll fit in any 9V battery compartment, like on the Serpac case of a portable Pimeta, or whatever. In an Altoid tin (as long as you take care not to short anything!)... basically anywhere a 9V battery goes. You'd have to make a hole for the USB connector, but those using the mini-b connector might not find that too objectionable.

Quote:

Edit: Also, how sure are you of stacking chips on top of each other? The USB 2.0 spec gives 2.5W although you can probably draw a lot more than that, but have you read TI's application note SBAA035A? I'm not sure of when anyone will be drawing more than 2W, so I don't think there'd be a case in which one will be stacking chips as you describe except for if they wanted 2W at 12V. Perhaps it will work by just stacking the chips, but the application note never mentions anything like that.


I'm positive stacking the chips will work. It's not TI-approved, of course, but neither is stacking BUF634s.
smily_headphones1.gif
You'd want to double the input and output capacitance with every chip you added, but otherwise, yeah. Inputs, outputs, and - most importantly - sync pins all get tied together, and Robert's your father's brother. That app note is for external sync, from a microcontroller or whatever. If you look in the DCP0* datasheet(s), you'll see the instructions for multiple chips in parallel, which is what we achieve by stacking them.

The stacked chips really is not for USB use, but for anyone who might want to use this with an alternative power source (5V 1A wallwart, or something like that). The 5V-5V, or 12V-12V isolation characteristics might be the most obvious application where you'd want more than 2W output capability. Most of the time it's unnecessary, but it's something that one person, somewhere, might one day want, once, and it costs nothing to support, so...
 
Mar 28, 2009 at 11:38 PM Post #52 of 66
I got the board today and after looking at the datasheet and everything I've got a couple of comments. (From here on pins 5,6, and 7 are referring to the three output pins on the IC from top to bottom)

If you are going to use a single output IC you can bridge C3 to get your + and - outputs to the terminals like intended on the prototype board without having to solder to the IC. Pin 7 has no internal connection so shorting 5 to 7 is no problem, again, in the single IC.

I don't think the board as shown above will work. Pin 5 you have attaching to the ground plane, that ground plane connects to both output terminals and if you solder both of those terminals in you'll end up shorting pins 6 and 7 to ground. In the dual IC that means you are shorting V+ and V- to ground and in the single that shorts 6(V+) to ground.

I like the lower design though. Not only does it help with the boutique crowd but allows the insertion of more capacitance after the regulator to control ripple. Looks like 4.7-10uF is a good place to be, especially if the IC is going to be run above 50% load.
 
Mar 29, 2009 at 1:42 AM Post #53 of 66
Quote:

Originally Posted by DKJones96 /img/forum/go_quote.gif
I got the board today...


That was fast!

Quote:

I don't think the board as shown above will work. Pin 5 you have attaching to the ground plane, that ground plane connects to both output terminals and if you solder both of those terminals in you'll end up shorting pins 6 and 7 to ground. In the dual IC that means you are shorting V+ and V- to ground and in the single that shorts 6(V+) to ground.


Huh? Maybe I'm just sleepy from dinner, but I'm not sure what you're saying.

Pin 5 is the ground - "0V" in the datasheet. There are capacitors between it and pins 6 (+V) and 7 (-V), which are there for noise reduction, et cetera; the only things it connects to, via the ground plane, is one pin of each of the output connectors - the ground pin.

How is that going to short anything?
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I think maybe you misunderstand the intended pinout - the connector nearest R1 is, from the top, (+V, GND). The other connector is unused for a single chip; if there's a double-output chip, it becomes (-V, GND).

Quote:

I like the lower design though. Not only does it help with the boutique crowd but allows the insertion of more capacitance after the regulator to control ripple. Looks like 4.7-10uF is a good place to be, especially if the IC is going to be run above 50% load.


Yeah, more capacitance almost certainly won't hurt, all other things being equal; I'd be curious to see how much it actually helps, if any.
 
Mar 29, 2009 at 6:34 PM Post #58 of 66
So you can cross connect devices.
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Let's say I want to put an alien DAC in an amp and use this to power the amp.
If I have access to the "data lines" I can just omit the USB jack on the Alien DAC board connect a few wires to this board and away I go.
And if people have no interst in the USB power option they can still use the board as an easy to mount USB jack.

(like this---> SparkFun Electronics - Breakout Board for USB miniB except you can pick between a full size and mini USB jack)
 
Mar 29, 2009 at 11:50 PM Post #59 of 66
Wouldn't it be a hundred times better just to use the, say, Alien/Bantam DAC as the USB interface, and run the power to this, rather than running USB to this and then running (unshielded) data lines around a high-speed switching converter?

There's room - just barely - to add a breakout for the data lines, but I'm unconvinced it's a good idea, let alone a good/desired addition.
 
Mar 30, 2009 at 12:30 AM Post #60 of 66
Meh, I knew the Alien reference was a bad choice when I typed it.
(it has a couple of spots that you can reliably tap the Vbus and ground plane but the other doesn't)
 
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