I’ve worked on this before and the layout did not work decently. In the past I depended too heavily on the LFPAK outline I grabbed from the internet. When I saw RMM take a crack at the problem (#3441) the truth is I initially dismissed his work: I thought to myself “shows what he knows, that stuff won’t fit.” Later the idea kept rattling around in my head again and it occurred to me that both RMM and I have built the A17DD-SO8 drivers and know exactly how much space each component needs. Clearly I needed to reconsider. Knowing how large the actual components are once installed on a driver like this makes a difference (as one might imagine :p).

Features:

• 0.5mm component keepout around edge. I may trim this up to a larger number in future revisions..
• FET + 1*7135: alt PWM is hooked up to the single 7135 so it may be possible to get this working with an unmodified version of STAR.
• No Zener! Sorry MT-G2 folks, you’ll have to stack a Zener across C1 or between D1 and R2. Or maybe kind of wedge it between R2 and the FET.
• Offtime ready.
• Large 1.5mm GND ring on bottom and on top (where possible). Exposed copper is 0.5mm on top and bottom.
• Like some other recent drivers, this driver does have a reverse-polarity protection diode but bypasses the diode for the voltage divider. Due to this we are able to use any diode desired. Ideally we use a protection diode with as low a Vf as is reasonable.
• The exposed spring pad is 10mm. Total pour diameter is 12mm.
• LED +/- pads are 2.0mm in diameter. They’re on much larger pours and diagonally across from one another.
• Some symmetry & stuff here and there.

v003:

https://oshpark.com/shared_projects/I16olxS2

v002 WIP screenshot (just for show-and-tell):

• Pulled components back in for an ~1.0mm ‘tall’ component keepout around the edge. (7135 tab extends to no closer than 0.5mm of the edge.)
• Changed LED+/- pads from 2.0mm to 2.5mm
• Revised silkscreen (added orientation mark for MCU, moved identifiers, increased text size, etc)
• Removed ‘stop’ designation on BAT+ vias for aesthetic reasons. (.. aesthetic reasons is also why they were on the stop layer in the first place, heh.)
• Changed 7135 outline to one which has a center pin.

v006:

https://oshpark.com/projects/s0JdAzw7

pilotdog68 wrote:

So it’s titled WIP, but how close is this to “release” status?
.
.
My X6 triple project is begging for it…

As far as I’m concerned it’s a WIP until at least one revision is actually assembled and working.

Exactly the same cart as the A17DD-SO8, plus a single 7135. Refer to page 2 of the AxxDD-SO8 thread for the cart links.

I forgot to mention that those vias are extremely close the the edge of the board. If there was a problem, that’s where I’d expect it to be. That’s something I expect to tweak. I don’t think that OSH Park will fail to plate the vias, but the GND vias do not meet OSH Park’s design rules. Assuming that the vias are drilled and plated this could result in only partial plating of the through-hole itself. It will certainly result in the vias not being entirely surrounded by copper on at least one side of the PCB (the bottom side). I expect the line to cut directly through the middle of the vias. What I expect is to see something like what led4power gets over here (but slightly worse): http://budgetlightforum.com/node/34812

pilotdog68 wrote:

Are the moon/low modes on the usual FET drivers really that bad?

WarHawk-AVG wrote:

Nice..single 7135 for low modes and a FET for DA POWAH! Awesome build wight…good job!

cajampa wrote:

Very nice wight, feels very balanced with the max POWAH and battery saving lows, i can’t wait to see someone build it, Would these work just like a A17DD-SO8 if the 7135 pad is not populated? It would be very interesting to see a comparison on run times for the FET on low from a A17DD-SO8 and this one. EDIT And Happy New Year guys

Yes, these will function like an A17DD-SO8 unless you do something to make use of the extra hardware.

DBCstm wrote:

Wight, for whatever reason the board outline doesn’t line up with the components when uploaded to OSHStencils.com. Really doesn’t matter as the actual cut out’s will be aligned with the pads to use it, just thought you’d like to know something is off somewhere. I don’t understand it, just use it and report it.

pilotdog68 wrote:

wight wrote:

Yes, these will function like an A17DD-SO8 unless you do something to make use of the extra hardware.

So theres really no reason to buy both boards right (except for Zener option)? I can just buy multiples of this one and use it for either driver?

• The A17DD-SO8 is easier overall to hand-build than this driver.
• One difference that stands out to me is the way LED+ bypasses are done on both boards. This PCB should be reasonably friendly to drilling a hole between C1 and the MCU without interfering with an SOIC clip much. The A17DD-SO8 can be drilled in the center of the PCB and hopefully not interfere with an SOIC clip.
• I don’t think that there is space for an LDO on this design, so I do not expect to produce a 17mm LDO version for momentary usage like I did for the A17DD-SO8.

Rufusbduck wrote:

Quote:

And i would think that if there is less resistance in the driver with this more expensive FET it should get less hot also.

Less resistance in the driver just allows higher current when the cell is fresh. The heat comes from the led so more current would mean more heat not less.

EDIT:

cajampa wrote:

Rufusbduck wrote:

Quote:

And i would think that if there is less resistance in the driver with this more expensive FET it should get less hot also.

Less resistance in the driver just allows higher current when the cell is fresh. The heat comes from the led so more current would mean more heat not less.

I meant that the driver should get less hot or is that never an issue on the FET drivers? i thought it was recommended to at least use a silicon cube on them. I know the led would get more current thats what i am hoping will happen.

cajampa wrote:

Thanks wight for clearing up my confusion, you are correct i had confused the two.
And now i know that a DD’s FET driver is stone cold, i had thought heat could be a problem nice that it is not. Is it possible to make a linear driver with this kind of FET and the attiny? or is that another animal altogether

Also note that led4power has built a linear driver called the LD-1 using this sort of FET and a PIC MCU rather than an ATtiny13A. All modes are constant current without PWM. Led4power’s driver is available for sale: http://budgetlightforum.com/node/34812

Crux wrote:

I’m still not used to the lack of a bypass cap at the aTtiny’s power pin (from pin8 to Gnd). My designs at work could save a lot of cost and space if IC’s didn’t require bypass caps… But, there are a million of these drivers out there – so its hard to argue. I’ll always find a way of adding these caps.

Crux

You can use the cap in the normal way (with positive connected between the protection diode and the MCU), but you’ve got that boost circuit problem at that point. To fix that you’d need a Zener diode pulling the boosted voltage back down on the MCU side of your bypass cap. By that time you might as well have implemented an LDO and used the output cap on that in lieu of the bypass cap.