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Driving a Cree Q5 LED with one NiMH cell - anything much better than an LTC3490?
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0xdeadbeef:
In an attempt to pimp up a cheap LED flashlight with a somewhat crappy driver, I first considered the obvious approach using a PAM2803 but then stumbled over the LTC3490 which seems a bit more efficient and doesn't need a shunt resistor or external diode.
I plan to use a voltage divider at its CTRL/SHDN input to be able to reduce the default current of 350mA to something in the 250mA-300mA range.
Admittedly the LTC3490 is quite a big more expensive than the PAM2803 but as I don't have any commercial interests, this doesn't matter for me. Plus, the LTC is actually easier for me to purchase.
My main concern is that I want to drive 250-300mA through the LED and the energy stored in one (!) 1.2V NiMH battery should be used as fully and efficiently as possible without depleting the battery below 0.9V.
Space is also a consideration as the PCB has a diameter of only 13.8mm and it needs to be single sided (placement wise) due to the battery/case contact on the lower side.
So in a nutshell: is there any much better step-up constant current LED driver for this purpose than the LTC3490?

The attached picture shows my current layout for a 13.8mm diameter PCB. Please ignore that DipTrace can't seem to display plated half-holes properly.
0xdeadbeef:
Well, OK, I guess this goes to show that nobody really shares my niche addiction ;)
Anyway, some pictures of the final layout with a more realistic render of the inductor used (WE LQS 5040). The model is a scaled down WE LQS 6045 though which doesn't fit 100% but is pretty close.
The voltage divider selects 250mA which I guess is bright enough and should improve efficiency and battery life when using a single AA NiMH battery (Eneloop).
There's also a spice model attached which indicate that an efficiency of ~80% is not totally unrealistic.
BravoV:
Subbed, keep us updated, especially the final result, thanks.  :-+

EDIT :

Just remembered there was an old discussion at CPF years ago, on adding a resistor at pin 5 and 6 (parallel with internal sense resistor) to increase efficiency, or boost the max current (2 cells configuration).
0xdeadbeef:
I can somewhat see how bypassing the sense resistor could boost the maximum current, but how would it increase efficiency in single cell configuration?

[EDIT]
Might take a bit longer. PCBWay suck. They let you select castellated holes with no extra price in the original quote but charge 5 times the original quote after the "audit".
I guess I have to remove the castellated holes from the design which is somewhat problematic.
0xdeadbeef:
The PCBs ordered about three weeks ago at OSH Park arrived today. I'm quite happy with the result, especially considering the price.
I paid $12.80 (free shipping) for 2x12 PCBs (smaller and bigger design for different flashlights).
I hope to populate a few of them this week.
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