Finally ! 
But why not attiny1616?
Wow, very nice!
Also, your KR1 looks freaking sexy with that optic!
The choice of the MCU is not too important; I chose the Attiny1634 because it seems like lots of people are fairly familiar with it now, given that it's in a lot of new flashlights like the Emisar / Noctigon ones, and the firmware development for it (Anduril 2) is fairly well supported and approaching stability.
However, you are right that I have my eyes on the Attiny3217 or any of the 1-series MCUs. Fairly simple change and perhaps I'll roll it in the next revision, but does require additional hardware for flashing as well which most folks probably don't have (many people already have the flashing kit provided by Intl-Outdoor).
Thanks, it is mesmerizing indeed, I'm glad with how it turned out. You need to see it in disco-mode with the Aux-LEDs (video in progress).
1616 is more recent, 3x3mm , cheaper and have everything we need.
Not a bad choice, and has a bunch of extra peripherals maybe I can take advantage of for future designs. 3x3mm QFN is useful for smaller drivers (e.g. 17mm), 3216 will have more flash for more features too. Thanks for the suggestions!
Very nice, I am also designing a boost driver based on the TPS61288, it’s similar to the MP3431 but with lower but still largerly sufficient 15A switching current, and a smaller package which is good for our small boards.
It’s taking quite a bit of time for me because I need to learn basically everything about electrical and board design.
Anyway I’m curious how you implemented ultra low level. What I came up with is to switch between two sense resistors with a NMOSFET, a low value one for the higher range, and a higher value one for the lower range, achieving a very large range.
Could you detail how you implemented it ?
Edit : where did you buy the TPS61288, I only see it on Mouser and they will have it only at the end of March.
I’ve been waiting for years for a driver like this and I’m extremely pleased to see it.
What’s the diameter?
ADDED: also, any chance of it being mass produced? 
EDIT2: I see XAL7020 on the pics but you mention a ~3 mm inductor. Could you clarify?
Markings are the same on a 7020 or 7030 for 2.2μH
Ah, so the number is inductance. Thanks for the clarification.
EDIT: Looking at the pictures I think that actually it may be a 6030 sized inductor. XGL6030?
Saturation current for XGL6030 2.2μH seems to be too low though.
Wow :+1: :+1: :+1: :+1: :+1:
Good lord, you continue to astound with your builds loneoceans. I’m most impressed that you managed to get such a low output using a current regulation scheme without any kind of circuit noise making it to the output. All my experiments in current-controlled low outputs have resulted in candlelight flickers as the switching noise makes it to the output. You must have a rock-solid control circuit going there - my hat’s off to you!
I also thinked these days that new TPS61288 is good candidate for future boost drivers and loneoceans just released today that new driver. Also is very interesting what type of feedback is used for measurement of such low currents. It is need to be very precise. I think is used very precise current sense amplifier and not just single low offset zero-drift opamp like in lume1 and GXB drivers where is work more like just current comparator. Critical here is the feedback compensation for stability of system.
Digikey have it in stock. I assume he buy from them or is used maybe free samples from TI.
Ah indeed they do, unfortunately they don’t do the paperwork to clear customs so I would get large fees upon delivery. I guess I’ll have to wait for Mouser.
Ho - lee - sheet
!
Very nice write-up and cool build. 
Will it be possible to build this driver like the GXB172 with a parts list and the PCBs?
Well great. Beside GXB172 that i cannot build, there is another one grail driver I will just watch in posts like these... bummer
What would the maximum power be that this driver can handle?
You said that you’ve configured it for 40 watt max for a single cell. But if you have multiple cells in parallel you can increase its power.
The input peak current is limited to 15A with the TPS61288, for a maximum fully regulated output down to LVP it doesn’t matter how low the DCIR of the battery is since you set the output current so that you hit 15A Iin peak at Vin=2.8~3V, maybe a bit higher if you’re fine with a dip at the end. That should be arround 35~40W depending on the efficiency and the inductor value. Or if you’re fine with a basically unregulated turbo it can be a bit higher.
But if you’re going to have several cells in parallel in a bigger light then you would use a more powerfull controller/converter or put several in parallel (the MF01 uses 4 boost converters for example)
This is so nice! Where do I sign up for few?