Nice work. I’ve also designed a driver around the TPS61288, it’s a bit different than yours though, it’s 17mm dual sided and intended to work with both E-switch and clicky switch. Parts are ordered and on the way.
One thing I don’t quite understand is why you are using a LDO? Are you using PWM though a RC filter? I’m not sure why you would do that with the ATtiny1616, is it to maintain Anduril compatibility?
It’s to give the MCU a fixed voltage supply so that the output PWM signal is also a fixed voltage (2.8V in this case), which is then filtered and divided down to Vsense.
But I have barely any knowledge of the MCU/firmware part, do you mean that with 1 series Attiny you can output a fixed voltage PWM no matter the supply voltage ? Or use the DAC maybe ?
Yes, the DAC. It’s what I use. I have not been using the 1616 specifically, I have used the 3217, but by looking at the datasheet it works the same way. I have just received an order with 1616s for my 61288 driver so I’ll find out soon enough anyway.
When using 2.5 voltage reference the DAC output is capped at 2.5V if MCU voltage is higher. Another benefit with the DAC is that it has better resolution than 10 bit PWM on the lower modes when using the 0.55 voltage reference. If requires some coding for smooth transmission between these voltage references if you want smooth ramping all the way through, but for me it’s worth the work to avoid LDO and RC filter.
That’s very interesting, indeed that means several parts fewer, unfortunaltely I really have trouble with coding in general, maybe one day I’ll have to learn, but for now I made it compatible with Anduril which output a PWM signal.
Are you getting reliable low levels when Vsense gets very low ? (See the discussion just above)
I do get a little instability on the lowest modes with 0.55 vref on my previous boost driver with MP3429. However, I did take your suggestion in the LumeX1 thread and added a second sense resistor and mosfet, so thanks for that. Space is a little tight on my 17mm driver after fitting the mosfet so I have been forced to “downgrade” to 1616 for this new driver, I couldn’t make it fit with the 3217.
Cool, glad it could help. But now with 2 sense resistors, one vref for the 8bit DAC should be sufficient ?
Are you going to use anduril with it (in e-switch mode) ?
Yeah, it’s a good suggestion, and looks like Loneoeceans method is the same. I could actually fit a tiny charge pump I’ve used before to keep mosfet resistance low, so I squeezed it in for the mosfet gate.
I only use my own firmware, for me it’s the fun part of the hobby. My firmware is E-switch, clicky switch and dual switch compatible as it is so no need for different firmware files for different lights.
I hesitated to use a charge pump gate driver like mic5019 to get a very low resistance, but I thougt that there was already enough parts, so I chose a mosfet that have arround 2.5mΩ at 2.8V, a bit expensive but not more than mosfet+driver. Ah but I forgot, the LDO is also to keep the mosfet resistance constant, without it the charge pump should virtually eliminate that resistance variation.
Ok, without the charge pump the LDO is probably a good idea. It’s the MIC5019 I have used, it works well but if you use it, make sure to put a pull down resistor on the enable pin. At first I didn’t, and the datasheet states that it can be unpredictable if the pin is floating. The datasheet was right.
Which mosfet did you choose? When do you expect your parts? I’ll follow this project with interest.
BSZ010NE2LS5
Good to know for the pulldown resistor.
Not sure, depends how much time it takes for shipping from Oshpark, also I haven’t made my order at Digikey yet, it’s the only place where I see the TPS61288 in stock, and it’ll have to go through customs unfortunately.
Ok, it’s the same mosfet that was in your schematics… I have ordered the same.
What’s the issue with Digikey? I ordered mine from Digikey.se, I got free shipping when buying over 50€ and UPS take care of all the customs. I only have to pay added 25% tax, but I have to do that when buying from Mouser too. The only difference is that Mouser add the 25% to the invoice that I pay. Digikey doesn’t add that, I get a separate tax bill from UPS with only taxes, no additional costs, end cost is the same. They don’t offer this service with Digikey.fr?
Hmm, I’ve never had a package with UPS coming outside of EU, but looking at other French feedbacks it is the same as DHL when the seller doesn’t take care of the VAT, they charge some customs clearance fees (like 20~25€) on top of the VAT, and it takes more time. Mouser is much better since they take care of everything, it’s like buying from the EU, initially I planned to wait until they receive the part, it was predicted for the end of March but got delayed to the end of the year 
Same in Sweden, if the seller doesn’t take care of it there is additional fee regardless of courier.
But in my case the seller (Digikey.se) takes care of the VAT via UPS. Only difference from Mouser is it’s a separate bill for the VAT. So for me ordering from Digikey is as easy as Mouser. UPS send me the VAT bill which I pay with Swedish bank app for quick money transfer, very convenient. Check with digikey.fr, send them a mail and ask. I would be surprised if ordering from Digikey.fr is more of a hassle.
I didn’t think to ask because on a local forum people advise against digikey due to that. They do ship with VAT paid when you’re business (have a VAT number).
For a long time I avoided Digikey for that reason, my first order in 2014 was indeed a hassle. But since then Digikey.se was introduced and last year I wanted some stuff that only Digikey had so I decided to give it a go and was pleasantly surprised. Now I don’t care weather it’s Digikey or Mouser, I order where the parts are which is very convenient.
Nice project! Anti flicker in moon level is the first problem solved in your driver? 
I think I ordered more 61288s than I need. If you want, send me a PM once your driver boards arrive from OSH Park and I can send you one or two. You can paypal me the cost once you receive it, no need for pre-payment.
Thanks you for the offer, I may still make an order from them as they have other a few other thing I’d like, but If I don’t I’ll PM you. 
Some news!
I received the last parts Wednesday (at last), yesterday I made one board, first time reflowing anything else than an LED but it turned out well :
This morning I tested the driver, only the hardware by bypassing the MCU :
And it works! The output voltage/current is stable, here is a quick output voltage waveform with the scope I just bought :
The only issue is that I got less current than expected, with 44mV ref voltage and 9.2mΩ (7+mosfet resistance) I should get ~4.78A, but I only get ~3.7A. After a quick check the real ref is ~43mV and the mosfet resistance is ~4.4mΩ which explains the difference. Swapping the resistance with a 5mΩ one should do the trick, but I’m worried about the ON resistance variation of the mosfet between parts.
Next I need to adapt Anduril for it.
