I played around a bit with that, and managed to get the '3680 ground on one layer. The other layouts will be a bit tougher to do, especially the '3652. Also put a better ground on the '3103.
But for all layouts, there's plenty of ground pour on the top, lots of vias connecting top and bottom ground, and the bottom ground plane has very few cuts in it. So I think I'm good, at least for "ground to ground" inductance and avoiding magnetic loops.
I was playing around with a Eagle plugin that generates a Sketchup model of the board, which is pretty slick. The board fits perfectly in a Hammond 1590N1 box, with a fraction of a mm from the sides and screw risers of the box. However, there's only about 8mm from the wire entry of the terminal block and the long side of the box. You'll basically need pliers or tweezers to stuff wires into the terminal block when you're wiring the thing up, unless I go with a 2 piece block.
Saturnus, how'd you run wires in and out of the Hammond box in your system?
A bit better explanation of what I meant, with some basic pictures to help illustrate. Plenty more examples of SMPS design as I do an awful lot of them and have worked closely with National Semi, Ti and Linears application engineers and others to get my layouts as near as perfect as I can and reduce any EMC problems. As stated I have just finished a LTC3789 design and spent monday with a Linear engineer going through every aspect of my layout.
Depending on the controller, the following notes are to help minimise the EMC effect of any switchers on the rest of the layout. With reference to the attached picture that help illustrate the points.
The GND that is part of the switching loops should be isolated on the same layer as the switcher components and joined to the main system ground at one point only by several vias, usually the thermal pad of the controller IC. (In the attached pictures, the vias are either side of the thermal PAD, this was a the request of production who had some worries over solderbility, newer issues of this supply have all vias within the thermal pad). This limits the high di/dt currents from the main PCB ground plane(s).
Again depending on the controller, it is recommended in most cases to avoid ANY copper under any of the switching nodes copper and the inductor. This avoids capacitive coupling of the switching noise to any voltage plane or signal. This is not often discussed in detail in data sheets and app notes, but is considered best practice when doing SMPS's. There are some exceptions, but the majority of layouts benefit from this practice.
Feedback, keep the feed back resistors as close to the device as possible and the traces between these resistor to the controller IC as short as possible, these traces and resistors should be one of the first things placed during layout.
Any current monitoring traces should be routed as true thevorin traces and the lengths of iether leg kept as near as possible the same length.
Regards
Marc
Depending on the controller, the following notes are to help minimise the EMC effect of any switchers on the rest of the layout. With reference to the attached picture that help illustrate the points.
The GND that is part of the switching loops should be isolated on the same layer as the switcher components and joined to the main system ground at one point only by several vias, usually the thermal pad of the controller IC. (In the attached pictures, the vias are either side of the thermal PAD, this was a the request of production who had some worries over solderbility, newer issues of this supply have all vias within the thermal pad). This limits the high di/dt currents from the main PCB ground plane(s).
Again depending on the controller, it is recommended in most cases to avoid ANY copper under any of the switching nodes copper and the inductor. This avoids capacitive coupling of the switching noise to any voltage plane or signal. This is not often discussed in detail in data sheets and app notes, but is considered best practice when doing SMPS's. There are some exceptions, but the majority of layouts benefit from this practice.
Feedback, keep the feed back resistors as close to the device as possible and the traces between these resistor to the controller IC as short as possible, these traces and resistors should be one of the first things placed during layout.
Any current monitoring traces should be routed as true thevorin traces and the lengths of iether leg kept as near as possible the same length.
Regards
Marc
RCA phone connectors. There's room for 3 (maybe 4 with a squeeze) in a row on each end above the board. If you need more connections, use mini-xlr that are (roughly) the same size as RCA phono connectors.
If you're in a squeeze don't use ternimal block unless it is needed. Use pin headers instead. That'll save up some PCB space as well. If you're still in a squeeze, turn the ternimal blocks 180 degrees. It'll make it a lot easier to insert multiple cables in that case.
I also note that you still have stand-off mounting holes. What are those for? You're going to use double adhesive mounting anyways.
Last edited:
Thanks for the info Marc, that's a pretty nice layout. I'll put a bit more work into the switcher layout and see if I can put together something better.
Saturnus:
I'm planning to bolt my card to the case using the four holes, and use single sided adhesive gap filler stuck to the bottom of the card. This makes the card removable - if you tried to pry the card loose from the bottom of the case with double sided tape, I think you'd flex and damage the card. Plus the holes aren't really in the way of anything, and someone else might find a use for them, so they'll remain until I have a good reason to remove them.
I think I'll do a 3.5mm pin header at this point, instead of a terminal block. You can solder straight to the pins, or plug the "plug end" of a 2pc terminal block into it if you want a terminal block.
To get wires through the case, I think at this point I'll say "leave it to the end user". I think there's too many connections here for RCAs or even Mini-XLR, but there's plenty of circular connectors available in the Digikey catalog.
Saturnus:
I'm planning to bolt my card to the case using the four holes, and use single sided adhesive gap filler stuck to the bottom of the card. This makes the card removable - if you tried to pry the card loose from the bottom of the case with double sided tape, I think you'd flex and damage the card. Plus the holes aren't really in the way of anything, and someone else might find a use for them, so they'll remain until I have a good reason to remove them.
I think I'll do a 3.5mm pin header at this point, instead of a terminal block. You can solder straight to the pins, or plug the "plug end" of a 2pc terminal block into it if you want a terminal block.
To get wires through the case, I think at this point I'll say "leave it to the end user". I think there's too many connections here for RCAs or even Mini-XLR, but there's plenty of circular connectors available in the Digikey catalog.
Make a list of needed and desired connections.
But I agree. Too many variables on how people wish to make connections, and what sort of connectors they want to use. It's fairly easy to fit 3 (or 4) 12mm holed connector holes to the case. 3 is best for case stability.
But mini-xlr comes in 3,4, and 5 connector types so there should be plenty. For example one 5 connector one for input L, input R, GND, SW+, SW- (the SW for the Awake switch which is either built into the input connector or separate).
List of signals...
Class D outputs = 8
Solar positive/ground = 2
Battery positive/ground = 2
USB power/ground = 2
Left/right/audio ground (different from power ground) = 3
Audio enable (tie to ground to enable) = 1
USB enable (optional - tie to ground to enable) = 1
Bicolor status LED (optional) = 2
Analog volume control (optional) = 2
Ground for the above four signals = 1
Class D outputs = 8
Solar positive/ground = 2
Battery positive/ground = 2
USB power/ground = 2
Left/right/audio ground (different from power ground) = 3
Audio enable (tie to ground to enable) = 1
USB enable (optional - tie to ground to enable) = 1
Bicolor status LED (optional) = 2
Analog volume control (optional) = 2
Ground for the above four signals = 1
Solar/battery share a common ground. Same ground is also used for USB power and user interface, but I'd suggest keeping solar/battery, USB and UI grounds separate if possible.
As of now, outputs can't be paralleled. I never really saw a need for the feature, the card can duplicate the same output on both channels accurately enough that you can drive two 4 ohm speakers in the same airspace. But if it saves four holes in the box, I'll give it a try.
As of now, outputs can't be paralleled. I never really saw a need for the feature, the card can duplicate the same output on both channels accurately enough that you can drive two 4 ohm speakers in the same airspace. But if it saves four holes in the box, I'll give it a try.
Don't bother. I won't be necessary for the vast majority of users, and for those that would potentially need it (half-boominator builders) they're probably better off using an amp more suited directly at their purpose instead. I think you've Swiss Army knifed it enough already.
Layout finished again! (ha)
Spent an hour toying with EagleUp/Sketchup, here's a render of what the final board should look like. Created a few parts for fun, couldn't be bothered to do all of them.
Tallest part on the board is the capacitor, which is 12.5mm.
In the process right now of going through passive component values, making sure everything is kosher and trying to minimize the number of unique values. I'll post the Eagle files when I'm done that.
Edit: The card is now called "the shiznit", on a co-worker's recommendation. "Dude, you gotta call it the shiznit. Why would anyone want to buy anyone else? It's the freakin' shiznit."
Spent an hour toying with EagleUp/Sketchup, here's a render of what the final board should look like. Created a few parts for fun, couldn't be bothered to do all of them.
Tallest part on the board is the capacitor, which is 12.5mm.
In the process right now of going through passive component values, making sure everything is kosher and trying to minimize the number of unique values. I'll post the Eagle files when I'm done that.
Edit: The card is now called "the shiznit", on a co-worker's recommendation. "Dude, you gotta call it the shiznit. Why would anyone want to buy anyone else? It's the freakin' shiznit."
Attachments
Olimex took too long, sent me a bad PO and then went on vacation... so I ordered from Seeed Studio's "Fusion" service instead. Getting 10 boards made for about the same price I was getting 2 Olimex boards for.
Crossing my fingers that the prototype boards work, so I have boards I can populate/sell.
Crossing my fingers that the prototype boards work, so I have boards I can populate/sell.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.