There have been several conversations about available buck boost drivers. So here ya go!
This is some artwork for a 17mm, 2.7-5.5V, 1A Buck Boost driver using the Linear LTC3454. The design is taken right from the data sheet. A PIC10F322 was added to run a bare bones kind of UI. Battery board copper on bottom layer/side. Man it was a tight fit.
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Parts are on there way, but it will be a few weeks at least before the boards would come in. I see this as an open hardware, open source, or even a BLF project. These switch mode drivers are still a bit of a mystery to me, so fingers crossed. Comments welcome!
Any chance of posting links for the parts and a file so we all can order some? Also, what is the advantage of this over a 7135 driver? As I understand it they are both very similar in operating range and in efficiency (both are linear).
I will work up a BOM with part numbers, and eventually the gerber files. Too bad OSH Park doesn’t have their share a project feature going.
The LTC3454 is a switch mode driver (not linear), and would be quite a bit more efficient?, than the AMC7135. The data sheet claims 85-90% efficient. Of course they cherry pick their data point voltage at 3.6V. I think the main advantage would be when fresh batteries are in play. The LTC3454 would buck down the extra voltage, while the AMC7135 would be burning it off as heat.
Click on the embedded link in the first post for the data sheet…
Oh, my bad. I just glanced at what you labeled the link as: "Linear LTC3454" ;) Once these start to become available count me in for one, I'm assuming this is one sided?
Now that I have stepped back from it, I see several opportunities to clean things up and get rid of some vias and bottom copper. That would be by moving the PIC and running the LTC3454 ground right thru the middle of the package.
Should allow the driver to run almost constant current so there’s no loss in brightness until the battery is depleted.
A amc7135 decreases in brightness once the battery voltage (taking into account battery sag) becomes lower than the vf of the led and other losses, at its set current becoming direct drive until the battery is depleted. If a quality battery isn’t used with high current draws the amc7135 can drop out of regulation rather quickly depending on current and the sag of the battery.
There are quite a few people here who have the ability to program the Atmel ATTiny chips and there are is quite a bit of source code for nifty drivers using it. Using that would be sweeter than a PIC design.
I anticipated this, and by some fluke the ATtiny six pin devices have the supply, gnd, and even the PWM pins in the same locations as the PIC. They both are SOT23-6 packages and should be a straight swap, although I haven’t tried personally. The spare pin is brought out to a thru hole pad. Lucky for the ATtiny folks who can use the MCLR/RESET pin as an analog input.
+1. Linear regulators seem to be a necessary evil these days. Many buck drivers need 2x16340 in order to regulate current to a white LED, and it’d be great to just use 1x18650 with a buck/boost driver.
All IC and passive components on the topside copper, but it is a two sided board. The bottom copper will accommodate a battery spring in the center, like a Nanjg 105C, and there’s the outside annular ground ring too.
Nickelflipper do you have a round about number on what the efficiency would be once the driver switched to boost.
Not going to hold you to it, just curious.
Edit: I guess I should have read the datasheet first. Says 90% from 2.7V to 4.2v
Read/look at graph a little closer and… at 3.1V in and 1A out it is around 78% efficient. 90% is only reached at 150 mA. At 1A the efficiency never gets above 85%.
Absolutely no room for an SOIC8 package. I can appreciate the programming situation isn’t so hot, no room for pads either, which is what I would prefer. The only thing that comes to mind is making up a SOT23 to DIP adapter gadget. I have SOT23 programming adapter for the PICKit programmer, which is kind of expensive to justify for the casual user.
My goal with a single board construction like this was to keep it simple, and top side only components. Maybe I’m not thinking hard enough?, I’m still listening.
Passives are 0603, with a couple 10uf caps 0805, inductor is 5.2mm which is a small form factor for 1.85A saturation current. The problem with some of these fancy LED drivers are is their high component count. My idea is to dap some solder paste on the pads, put it on the hotplate, done. So, a two sided component construction is not appealing to me.
Thanks Texaspyro, I guess I should have read on down the datasheet. At the top it says greater than 90% can be achieved. Well thats only at 150ma like you said. That was kind of the reason I was asking, boost circuits are usually not all that efficient.
No formal training in electronics, but have been doing it for my own projects for some time now. I have some parts coming for a 3A buck boost board, but getting the 1A board going is first up.
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