Single-Board Universal Module

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30 Mar 2015 21:31 - 30 Mar 2015 21:33 #30487 by moss
Replied by moss on topic Single-Board Universal Module
you are right, I'm wrong.
A second filter can be thrown in if needed. The "filter" in the data sheet is just the typical buck output circuit. Leave room on PCB and populate if needed. There are also special SMT LC filters that may work. I kept it simple.
Last edit: 30 Mar 2015 21:33 by moss.

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31 Mar 2015 03:44 #30516 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
Well, I tried, but I just don't have room for an additional LC filter on the board.
I was able to replace the LDO with the DC/DC converter and added in the required Inductor:

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31 Mar 2015 05:27 - 31 Mar 2015 05:29 #30518 by octagon
Replied by octagon on topic Single-Board Universal Module
If you follow the suggested TI layout to a "T" it should work as advertised, thermal vias "22uF" output, and all.

I guess you have the diode leakages under control.

Should additional filtering be needed, it looks like you could fit it on the layer one? A zero ohm jumper after the switcher can also be useful in troubleshooting, and can be used also for an inductor or a ferrite bead.
Nice work.
Last edit: 31 Mar 2015 05:29 by octagon.

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01 Apr 2015 04:18 #30602 by mwm
Replied by mwm on topic Single-Board Universal Module
I stumbled across this while looking for servo controllers. They seem to have found a way around getting FCC certification for their DYI RF board.

I'm not sure how legal this is, or if it would apply to the universal module, but if someone were serious about making and selling universal modules, it would probably be worth their while to discuss this option with a lawyer.

Do not ask me questions via PM. Ask in the forums, where I'll answer if I can.

My remotely piloted vehicle ("drone") is a yacht.

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01 Apr 2015 04:54 - 01 Apr 2015 04:55 #30604 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I think it may be perfectly legal. The problem is that the FCC regulations aren't clear, so there is no way to know and the penalties for selling a non-compliant device are very steep. That is just too much risk for me to personally bear.
Last edit: 01 Apr 2015 04:55 by PhracturedBlue.

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01 Apr 2015 07:52 #30606 by Fernandez
Replied by Fernandez on topic Single-Board Universal Module
b.t.w. They use also rf filter at the output;
www.pololu.com/picture/view/0J3333

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01 Apr 2015 14:54 - 01 Apr 2015 15:03 #30619 by octagon
Replied by octagon on topic Single-Board Universal Module
I took a look at the switch layout, and the new one is not in the repo, so I cannot see everything well.
But from what I can see there are a couple of things I'd do differently.
The footprint for the TPS62172 looks different than the datasheet, which also include two vias in the center pad. This I got burned on, trying to eliminate on this size part. With vias in the center pad excess solder will suck down the part to the pad, which otherwise may be rocking and rolling on the center blob, not making contact with an edge.

The two larger holes for the USB connector can be vias, tied to ground for better thermal and electrical grounding, I think these are holes for the plastic bosses in the USB connector.

The footprint geometry in the datasheet looks different, and I would follow it exactly, paste mask and all. There is not too much wiggle room on 2x2mm parts.
( Making the pads a little longer helps if you have to hit the lead-less part with a soldering iron tip.)

The traces on the VIN and EN can be combined and made wider, like the app-note.

The grounds on the CIN and COUT and very close to each other, there may be a circulating current between them so I'd keep the as close as possible.

Here is rough sketch.
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Last edit: 01 Apr 2015 15:03 by octagon.

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01 Apr 2015 17:08 - 01 Apr 2015 17:28 #30629 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
Sorry. I checked in the latest design. You can take a look now.
I have tried doing a layout as you suggest, but I end up with a longer node attached to SW, and the loop from SW->L->Cvout->PGND is significantly longer. the layout guidelines do not specifically call out sharing the Vin and Vout cap gnd, but do indicate a single-point ground, as well as that the Vin Cap should be close to PGND and also (from above) that the Vout cap should be close to PGND.
getting vias on the pad will be challenging as well.
Here is what I was able to do (it isn't yet clean, just a proof of concept)

FYI, I used the SparkFun library for this device. I agree that it'd be better to use elongated pads like we did for the other QFN parts
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Last edit: 01 Apr 2015 17:28 by PhracturedBlue.

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02 Apr 2015 01:07 - 02 Apr 2015 01:13 #30659 by octagon
Replied by octagon on topic Single-Board Universal Module
The extra trace length on the SW pin to inductor could increase inductance which is OK, but loop size, and DC resistance is more important, generally, but for this little guy I'd think its OK.

I did not update the PS1 lib's smd sizes, according to TI, just added two vias and a larger center pad.

USB holes I changed to (0.9mm) vias. Top side routing changed a little.

I'm ignorant of the mechanical constraints. Do you have a .step file of the case?

bitbucket.org/deviationtx
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Last edit: 02 Apr 2015 01:13 by octagon.

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02 Apr 2015 01:26 #30662 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
can you provide your lbr/sch/brd file?
It looks good to me.
I don't have a case design. There aren't really any mechanical constraints other than thatthe board cannot shange size, and noen of the connectors can move. The USB can move a small amount if neededas it isn't critically placed, but I'd rather move it as littel as possible.

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02 Apr 2015 02:04 - 02 Apr 2015 02:08 #30665 by octagon
Replied by octagon on topic Single-Board Universal Module
If you want a better isolation between the power sources, with "no" loss, smaller, and maybe same price, you could use two pmos FET's.Gates can take +-20V, drain 30V. www.digikey.com/product-detail/en/SI2369...-T1-GE3CT-ND/4327755
I could upload those files, but I want to fix that TI layout first.
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Last edit: 02 Apr 2015 02:08 by octagon.

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02 Apr 2015 02:39 #30666 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
cross coupling the devices means no power if both USB and devo power are on at the same time. I prefer the current solution where the board can function in this mode.

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02 Apr 2015 03:18 - 02 Apr 2015 11:21 #30667 by octagon
Replied by octagon on topic Single-Board Universal Module
You probably solved the Schottky diode issue.
If both supplies are ON, the the intrinsic diode takes over, cutting out like 0.55V. The file below can be used with LTspice.
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Last edit: 02 Apr 2015 11:21 by octagon.

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02 Apr 2015 18:06 #30702 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
Recently I've been trying to get the PPM input working on the UTx board with Bluetooth & Smartphone integration. It has been mostly working, but the servos were jiggling like crazy. I finally root caused this to the PPM ISR not providing accurate timing. This has to do with interrupt priority. The PPM input is supposed to have highest priority so that it can accurately capture the time that an event happens. After screwing around with it for a couple days, I figured out that the libopencm3 set_nvic_priority doesn't actually work on the STM32F0. That means that the PPMIn timer is waiting until the SPI transmit completes which significantly impacts accuracy of the pulse-width. I think I have it all resolved now. This was the last major feature I needed to ensure theboard design is suffcient for all use-models.

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02 Apr 2015 22:28 #30713 by Jasenk
Replied by Jasenk on topic Single-Board Universal Module
Excellent news!

-Jasen

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02 Apr 2015 22:32 #30714 by JustenCase
Replied by JustenCase on topic Single-Board Universal Module
+10 :woohoo:

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03 Apr 2015 14:30 - 03 Apr 2015 16:44 #30748 by moss
Replied by moss on topic Single-Board Universal Module
Using two p-MOS-FETs rather than two schottky diodes would also eliminate the need for a solder-in "LDO bypass" component, as the loss of the FETs (~30mΩ) and the 100% duty cycle of the TPS62172 (with a 430mΩ @ 3V switch) would be low enough not create too much voltage dropn (~100mV) with a 3.3V input.
Of course with both power supplies active, the p-FET diode drop takes over.
Last edit: 03 Apr 2015 16:44 by moss.

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03 Apr 2015 15:16 #30749 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
That is a good point. I like the idea of supporting 3.3V to 12V with no board modification.

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03 Apr 2015 22:03 - 03 Apr 2015 22:09 #30770 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
I've updated the board with x-coupled pfets. The files are all checked in. I think I made all the changes octagon recommended as well Please let me know if you see anything wrong.

Last edit: 03 Apr 2015 22:09 by PhracturedBlue.

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04 Apr 2015 00:53 #30774 by PhracturedBlue
Replied by PhracturedBlue on topic Single-Board Universal Module
Is there a significant difference between band-pass filters?
The RFAxis comparative analysis recommends a TDK DEA162450BT-1260B3, however, Murata makes a LFB182G45SG9B740 with roughly similar specs which is much cheaper. I don't know how a band-pass filter will compare to the Pi-filter I've currently got on the output

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