I can’t help with the design but I’d love to see this project happen. I would also hope a bigger than 1k MCU is chosen.
I can’t help with the design much either, but I can sure stuff em in a light and put lots of power to em to see how they work! 
Carry on…
No, you’re not an EE but you make very nice crash test dummies.
I prefer CC as well. I’ve been planing to add a turbo DD fet mode to a standard 7315 design. Sometime. 
When I’m through with other projects.
I think this can work, even with the attiny13a although I haven't tried it yet. I imagine you would use PB0 and PB1 as the output pins, driving the 7135s using PWM on the lower modes then switching PB1 off and PB0 (connected to FET) on to 100% PWM for the highest mode, or even at partial PWM for in between modes depending on how many 7135s you are using.
Attiny13 has a 2nd pwm capable pin so you could add pwm FET.
I have the urge to move up from the attiny13 though.
Just looked it up the 25 (2k), 45 (4k) & 85 (8k) are all the exact same package/pinout.
Attiny13 is SOIC 150mil. Others are a bit wider SOIC 208mil. If needed you can squeeze them onto attiny13 pads by bending the legs down.
I use Attiny25's on almost all of the drivers I make but I use the 13's footprint when designing the boards (no particular reason why other than I had that library already). I've also used 25's on NANJG drivers without any problems.
Simply put, they are interchangeable.
Just need some of these coding geniuses to whip up custom firmware for the Tiny25 2k platform
Like 4 group driver like the 2 group Nanjg
1 group Lo/Med/HI w/ turbo timeout
2 group Lo/Med/HI
3 group ramping w/ double tap(or long press) turbo w/ timeout
4 group whatever they can think of
(hidden strobe in all modes)
Attiny25 comes in both 150mil & 208mil width. :zipper_mouth_face:
Yeah the package is the 20SSU from memory.
What is 150 & 208mil measures of? Not doubting as I’ve never even seen any of them other than the 13A but I looked up the datasheet’s earlier and according to them the dimentions (of the SMD variants) are exactly the same.
Body width. 208 mil = 0.208 inch or 5.28mm. The title box on that datasheet page says 8-lead, 0.208” Body, Plastic Small Outline Package.
Its easier to see what package they are available in at each chip’s page on atmel.com under the “ordering codes” section. Attiny13 & attiny25 150 & 208, attiny45 & attiny85 208. Here is an attiny85 with bent leads on a nanjg driver The TV-B-Gone flashlight build post #19.
When I lay out a board, I try to stack both the 150 mil and 208 mil footprints on top of each other… that way I can use either package without having to resort to pin-origami.
Ah yes, my mistake. Only the 25 has a footprint that will fit NANJG boards. The others are too big.
- Matt
When I’m making a board for myself I like to squeeze things in. Pin-origami for me. 
QFN? Na.
Yeah I can solder QFN, but I try and always fit leaded packages first. Makes programming easier too as I don't need to worry about breakout pads.
There is a 'wide' version of the tiny13, which is the same size as the tiny85. But there's no 'narrow' version of the tiny85. Or something like that.