[WIP] 15mm PAM2803 w/ ATtiny13A rough layout / possibility

Heh, maybe the “more striking” bit is a concentration aid for me. :wink: I use the default cursor which is “inverted” from whatever it’s hovering over (black = white, red = blue, green = pink, etc). Since I was curios I checked it out on both backgrounds just now. I actually find the cursor easier to see on the black background. Did you check out the “Large” cursor while you were in there?

No, just the background color. I’ll have a look next time I’m in there.

Liftoff, we have a liftoff…

15mm boost driver (v1) working

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Partlist and used Firmware below

Rebuilt on a 2nd board, running fine.
2x 2AA and 3x 1AA (Eneloops) drained so far, about 200 mode changes, all good.
It’s a HQb15 de-luxe with Coilcraft inductor and high value capacitors.

Board is the same layout as in post#72 above.

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Oshpark link for HQb15 v1 EDIT: Obsolete as HQB15 v2 is finished, see post#96


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Driver height with this inductor is 3.7mm (0.2mm less than with the FT inductor). Now take the new Oshpark 0.8mm boards and you’re down to 2.9mm. That’s a whopping 3.0mm less than a Nanjg110.

Enough space around the Attiny13a for the clip after driver assembly.

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Partlist
(source in brackets; see post#25 for more info on the parts)

Switch: PAM2803, SOT-23-6 (FastTech driver)
L1: 2.2yH, Coilcraft XFL4020 (electr. supply)
D1: BAT60A (electr. supply)
C1: 10yF, 0805, X5R (electr. supply)
C2: 20yF, 0805, X5R (electr. supply)
C3: 4.7yF, 0603, X5R (electr. supply)
R1: 0.120Ohm, 0805 (FastTech driver)
R2: 150kOhm, 0605 (FastTech driver)
R3: 33kOhm, 0605 (FastTech driver)
MCU: ATTiny13A-SSU, Package 8S1 (electr. supply)
OTC: not yet
FET: (FastTech driver)

C2 and C3 are by design in parallel (C2 for PAM2803, C3 for ATtiny13A). In this built I used both caps and with high value.

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Firmware

An adapted Dr. Jones MiniDrv firmware for starters.
Frequency changed to 18kHz, on-time-memory, 9 modes

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Output

Eneloops fresh from charger (no resting time)
With 2AA holding ~780mA for quite some time (R1 (=Rs) = 120mOhm)
With 1AA starting >550mA, continuously going down, but surprisingly slow in comparison to Nanjg 110

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loose threads…

no OTC yet
adapting R1 to change output
output at PWM1 is 16mA with fresh cells (1AA and 2AA)
trying different components (inductor, FET)
17mm version

15mm V2, will be a fine tuning of the layout after having built them twice
V1 has an overall size of 15.4mm, the GND copper layer by Oshpark is only 14.8mm. V2 will be increased to 15.6mm.

(EDIT needed after Drupal overhaul)

Wow! Wow! Can’t wait to see the progress!

Looks great. Will you be testing efficiency?

Nice!

Maybe add one or two more gnd vias at the fet for the next version.

@HarleyQuin

That is some really outstanding work! I’m excited to watch as you develop the design.

Good work! Looks like your motivation has been boosted a little. :wink: Did you use fresh components or are these just moved over from the badly behaving board in post #57? Clearly it is a different inductor of course. Have you developed any idea of what went wrong with the last build?

Now I’m pretty excited while waiting for parts to show up. My layout definitely needs some work to accommodate the two ‘extra resistors’ discussed recently… unless it just works and then I don’t care. :wink:

Efficiency is kind of a moot point if you can’t find a driver with these capabilities elsewhere. The PWM modes + PAM2803 are the same way DQG handles the situation IIRC. It’s also difficult to “test efficiency” when you’re doing PWM like this, except on 100% PWM (always on / high mode).

That said, I’m sure we’ll look into that at some point. (at least for 100% PWM)

Once we get a handle on this stuff the next questions are:

  • whether we can use PAM2803 on a larger PCB (17mm etc) to drive a P-Channel MOSFET. (so the internal MOSFET or FET or whatever in the PAM2803 would act as a gate driver I suppose). If we can get that to work we may be able to squeeze a little higher current out of a larger board but still work with 1xNiMH or 2xNiMH
  • whether we can remove or tamper with “VOUT” to get >5v output. Of course this is automatically a problem for the ATTINY and so might not be a great idea… but it’s an interesting question and if it came down to brass tacks a few diodes of the appropriate type could drop the ATtiny’s supply back from say 6.5v down to a safe 5.5v. That might be a workable way to get ~6v out of 2xAA or 1xLi-ion. Realistically I don’t think we’ll be doing much along those lines. Boosting from 2xAA to 6v isn’t going to be efficient at all and will be harder to spec components for I think, besides the fact that we’d be running stuff out of spec. Boosting from one li-ion to 6v can already be handled with a different boost IC.

Really I’m just interested in the second bullet point from an academic standpoint. The first though… that could get fun!

Hi Alex, just looking to get a baseline since hopefully there will be others to compare it with at some point.

Thanks for the encouraging comments.

True.
Knowing there is test-personnel standing by :wink:
It’s only that wife and kids are now wondering why I’m so absent minded again, not paying attention, mumbling strange words like sense resistor and redundant components.

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I can’t provide data as HKJ does in his tests. Best I can do is I-in vs I-out. Even this has already proven to give different results depending on the eneloop used (hot from i4 charger or resting from Opus-charger). My testing procedure isn’t remotely accurate enough to invest time here.

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The working second HQb15 v1 has no parts of the first one. I laid the 1st one aside after already checking continuity and having resoldered where I could with the iron - to no effect.
The 2nd one was a complete fresh start. New board, new FT driver, new components. Testing continuity on the complete board, testing the FT driver before desoldering (hadnt done that with 1st one) and taking unused additional parts.
My best guess for the 1st one: Bad solder connection / not enough solder paste somewhere. Perhaps a faulty component as a distant second.

For now I’ll leave R2 and R3 in the design, but I’m couriously expecting your test results.

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Could you kindly explain the reason behind this. Unless I’m mistaken (and I could very well be) in this boost circuit the FET does not draw current directly from GND. It’s coming via Pin3 and Pin2 of the PAM2803. I might thicken this path, though.

V2 inbound, thatfor I’ll skip V1 link.

@HQ - sorry if this seems obvious or I’m missing something but if the negative connection to the battery tube is on the spring side then current from L- goes through the pwm controlled fet from drain to source and then through the board. Other components are grounded as well but the vast majority of the ground side current follows this path and just as the positive side needs short, generous traces/vias along the Vin - Led+ path, so does this. There are other gnd vias sure but straight through from the fet is the shortest path. Not a big deal at low current but still something I would normally suggest.

This is where I have more interest.

But it’s great to see the drivers built by this community growing!

@RBD
Thx for explaining your thoughts. The through the board part was indeed obvious to me. It was the at the FET part, which I translated to: bottom right of the driver, that made me wonder. I think the current goes from L- to FET to PAMpin3-pin2 to the left center of the board, so vias at the FET sounded odd.
Anyway, I added vias. Doubled them, actually. Even made them symmetric…

So here is HQB15 v2.
This board is provided as is, and yet untested

Oshpark Link

Partlist and Firmware see post#84

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Changes from v1 to v2:
Size increased to 15.6mm, the copper GND ring should now result in full 15.0mm
PAM2803 now has a Pin1 dot that appears on the board
Several component positions slightly adapted
A lot of paths widened
GND vias doubled and rearranged

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The yellow circle is not in the actual board, it just indicates 15.0mm

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Will this driver survive a liion like most other boost drivers nowadays, or will it release the magic smoke?

@gisewhcs - It’ll probably survive, but for now that is certainly not important to me. I can’t speak for the others who are working on this. As far as I know, this normally results in unregulated PWM-adjusted output levels which aren’t as bright as DD. I should already have a 15mm DD+1 driver somewhere, check the list in my signature. This driver also does not have a voltage divider. It cannot measure battery voltage and has no LVC / LVP.

If we achieved programmable regulated no-PWM output on a double sided or 17mm board (by biasing the feedback pin) I think that a li-ion cell becomes more of a problem. In that case the li-ion would probably eliminate modes in addition to it’s other drawbacks. I haven’t fully considered this statement, so it may not be true.

I just had an idea. I know this idea I just had is nothing like the intended purpose of this driver, but I don’t know a better place to ask about it. What would be the feasibility of building just the boost circuit into a tailcap pcb? I was looking at PD’s lit tailcap thread, and lots of things are going on there, but this idea wouldn’t fit there at all. If the boost driver could be fitted to a tailcap pcb, then the actual control driver in the head could provide all the modes and such that we’re accustomed to having in our lights. The tailcap would be the only part that would have to be modded, and the “danger” of li-ion going “direct drive” through the boost circuit would be moot, since the drivers we use take “direct” power from li-ion on their inputs anyway. Can this be done? Is it worth doing? I just thought being able to simply add boost capability to any light at the tailcap would be a neat thing to do.

That puts the LED on the low voltage/high current side of the boost circuit. Not sure what the point would be.