OPEN Source: Tiny, high-current, boost driver (that is starting to work)

OPEN Source: Small high-current boost driver (that doesn't work yet.... EDIT: that is starting to work)

(my initial board design is under 12 x 8 mm)

I realize this is like opening presents on Christmas and finding a bunch of broken toys. I had good intentions for this boost driver design, but beyond testing the first iteration (which didn't work), I just haven't had (and won't have) time to revisit it. So, for whatever it's worth (and I apologize that the worth may not be much), I'm open-sourcing the initial schematic and board layout I created. However, to perhaps save this thread / driver from absolute uselessness, I will make one useful offer:

If anyone iterates this design and contributes a version back to the thread that the forum (or at least the thread participants) think is worth testing, I'll send them a couple of the ICs for free to help that testing along.

I have a small handful left, and I can probably send a few, to a few different people. This will at least give someone a slightly easier path to tinkering, because the IC is the only tough part to get a hold of. That IC by the way is the FP6298, a Low-Noise 4.5A Step-Up Current Mode PWM Convertor. As far as I can tell, this IC hasn't been discussed or used on LPF before, so we're not stepping on any toes. Datasheet here:
http://www.feeling-tech.com.tw/km-master/ezcatfiles/cust/img/img/24/fp6298v063.pdf

Schematic and board files are attached (but remember, there's likely something wrong with my implementation, because the initial prototype didn't work as expected). Digikey part numbers for the inductor, diode, and capacitors I used are added to the schematic as text comments.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

This is neat. I've had a few of these kinds of ideas before too, unfortunately. Not this specific IC, mind you, but boost drivers that should have worked but didn't. But I typically try to stay away from the ZXCT1009 nowadays because of the overshoot.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

^I'm sure you could get rid of the overshoot by adding a filter of some kind. A cap from the load to the feedback pin for example would cause the FB pin to read higher at startup and therefore lower the output current until the cap charges. Fine tune it with resistors in parallel and/or series with the cap.

rhd, I looked at the datasheet, and I'm not sure what "floating available" means, but later on they explicitly say you need a resistor on the over-current pin - 26k in this case.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Cyparagon said:

rhd, I looked at the datasheet, and I'm not sure what "floating available" means, but later on they explicitly say you need a resistor on the over-current pin - 26k in this case.

Click to expand...

Good spot.

Let's try this - let's walk before we run (or crawl before we walk?). Instead of trying to get the ZXCT1009 incorporation perfected before we know if the underlying driver setup works, why not try the driver configured as a simply (if less efficient) traditional constant current setup, with all of the current going through a sense resistor to generate the full 0.6V feedback drop. Here's a simplified board.

It will waste 1 to 1.5W of power as heat, but that's okay if we use a 2512, and it's just for testing / development purposes anyway.

I've included digikey part numbers for everything (except the IC which they don't sell) in the schematic.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

You're just asking for oscillations by putting a cap from output to feedback. Leave it from output to ground.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Cyparagon said:

You're just asking for oscillations by putting a cap from output to feedback. Leave it from output to ground.

Click to expand...

I set it up in that configuration because I believe we found that in testing the original Open Boost (or "Ben Boost") that a cap to GND was less effective.

In any event, I made a variant for testing that connects the cap to ground.

I also changed the dimensions from 16x9 to 12x12

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Hey rhd, I think youve got it the wrong way around, we found that the cap between LD+/LD- caused oscilations and only the cap to gnd should be used.

Heres my foolproof zxct1009 schematic, its never given me any trouble before:


Seems to be in line with your usage in the first post. I need to look over the datasheet again, but the voltage you are getting from the 0.02 resistor might be too small for the zxct?

Did you ever get a chance to test the last board you posted(direct resistor current set)? This IC looks promising if you can get it to work.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

slightly off topic:

You can use the export function ( file → export → image ) in Eagle so that the screen capture won't show the origin ("+" near all parts and added texts) and results to a cleaner, more professional looking drawing.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Thanks for prompting my interest in this again Ben, I've had the boards sitting here, but haven't had the time or interest in reflowing any for a while.

But I did this morning over breakfast, and I have some good news. This design (attached) works! I reflowed one board set to 600mA and it worked great, so I added some resistors in parallel and kept increasing the output current to 1.6A, and it was still doing just fine.

This version uses a simple resistor to set feedback, and with a 0.6V reference voltage, that takes a hit on efficiency (but it's perfect and usable for 520 B1s, and 5.6mm 445s even as-is. I was crazy for not kicking the current up to 1.8A this morning, because I'm sure that's the current point everyone wants to know about, but I wasn't thinking. Still, I'm sure that if it did 1.6A, 1.8A is fine too (heck, 2.4 might be).





Next step, lets get the ZXCT in here

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

(intentionally double-posting to add clarity to which version I'm discussing)

Here's a potential V06 that takes the version I just tested above, and integrates the ZXCT1009 back into the design.

The reference voltage of this IC is 0.6V and I'm using an RSENSE value of 0.05 ohms. If I've done the math correctly, I think the RSET value calculation can be simplified to:
RSET = 1200 / Current
(where the units are ohms, and amps, respectively)

If this schematic looks logical to everyone, I'll do the board layout:

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

rhd, you said you had a few of these ICs, and I was wondering if I could get a couple from you? I would happily pay you and shipping. I want to see if I can get some lower current out, which is the opposite way you are going on this. I see real potential for a lower current driver in the 400mA to 900mA range. If this is doable, PM me and we'll get together on it. Thanks.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Awesome, if it works with the fixed resistor we can probably get it going with the zxct just fine. I'm going to put in an order at oshpark for that board. When I get some free time later I might try to throw together a pot adjustable revision.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Here's the board with ZXCT1009. It's V07. Unless anyone spots problems, I'm going to order a couple later tonight.

At 12x12 mm, it's not tiny, but if you take a look at the layout, there's lots of room for miniaturization / optimization. We may be able to find a smaller inductor and diode, and going to 4-layer would allow for the removal of at least one space wasting trace. But that's not really a priority for me until at least this revision is tested.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Ben, my thought exactly. I think this can easily converted to an adjustable driver. I'm not sure I will need the ZXCT1009.

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

paul1598419 said:

Ben, my thought exactly. I think this can easily converted to an adjustable driver. I'm not sure I will need the ZXCT1009.

Click to expand...

How would you make it adjustable absent the ZXCT ?

Re: OPEN Source: Tiny, high-current, boost driver (that doesn't work yet)

Well, this is just a thought right now, but I'd put a 220K resistor in series with a 500K pot at pin 2 to ground. At the cathode of the schottkey diode I'd put two resistors and a pot in series to ground. First from the cathode would be 10K, then a 27K pot, then a 64K resistor to ground. The 10K resistor would be tied to pin 6 of the IC. You should be able to get 2.2volts to 6 volts out, at around 350mA to 900mA out. The LD would be tied to the cathode of the diode and ground. There would be a single cap to ground on the LD positive lead.