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

Hi wight,

that’s a nice one. I like the idea of a “Nanjg 110 with modes”. I built some lights with the Nanjg 110 as it seems to be the best of the bunch of 1-cell-boost-drivers and I prefer Eneloop-torches for the kids.

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Some ideas for the layout:

Why suddenly PAM2805? 2803 and 2805 are not pin compatible and your circuit in post 13 follows mostly the 2803 datasheet circuit, except for the capacitor between Pin-1 and GND. No such with the 2803. The 2805 has its input capacitor there, as Vin for the 2805 is Pin-1.
The output capacitor for 2803 is between Pin-5/Diode/LED+ and GND, so it in fact is at the same position as for the MCU capacitor. This Cap might be disposable, one could as well use a higher value for output capacitor (22yF) as the datasheet suggests for “high power” LED - I think they a referring to 750mA.

Any particular reason for PWM using MCU Pin-5? As Pin-6 is the usual rail for pwm in our firmwares and as we’re not using multiple rails on this one we might just stick to pin-6.

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I want to do a test setup with a Nanjg 110 and a stripped Nanjg AK47 to see whether the design will work at all.

I have all parts except for the FET. Could someone please give me some specifications for the FET. I have only a faint idea what is needed here as up to now I don’t use FET/DD drivers.

One that I think might fit the pin layout and spec is
IRLML0030TRPbF
Power MOSFET
N-Channel
SOT-23-3
UDS 30V
UGS (th) +/-20V
Id 5.3A (4.3A at 70°)
RDS (on) 27mOhm (40mOhm at 4.5V)

That one ok, or any value that could be better than on this one? Or any other value that has to be observed?
Thanks a lot.

To make part selection easier I made a more detailed partlist according to wight’s design as of now and following the recommendations in the PAM2803 datasheet. Suggestions and corrections are welcome.

PAM2803
SOT-23-6

Inductor
min. 2.2yH, 4.7yH recommended, DC resistance (DCR) as low as possible
4mm x 4mm / 5.4mm x 5mm

Diode
Schottky, min. 2A, Vf as low as possible

Input Capacitor
min. 2.2yF, X5R or X7R recommended
SMD0805

Output Capacitor
min. 6.8yF, 10-22yF recommended, X5R or X7R recommended
SMD0805, perhaps increase to SMD1206 for 10-22yF on a 17mm board

Current Sense Resistor (Rs)
~0.120 Ohm for 750mA (2cell)
SMD0805

ATTiny13A-SSU (MCU)
Package 8S1

Capacitor for the MCU
(might be unnecessary as being in parallel to Cout)
10yF, X5R or X7R
SMD0805

Off-Time-Capacitor (OTC)
1yF, X5R or X7R
SMD0805

MOSFET

This seems to work.

I hooked up a stock Nanjg110 to an ATtiny13a, and a Cmcu, both remainder of a Nanjg AK47. I added an OffTimeCap between Pin-2 and GND. And I used the FET I described 2 posts before. I placed the FET on the pads for a 7135, cut the traces and rewired (better: re-blobbed) for the PWM signal from Pin-6.

I flashed a it with an offtime firmware with 4 modes.
And there was light.

First impressions:

It does work on two tested frequencies:
PWM at 4 kHz (9.6MHz CPU, divider 8, fuse 6a) had a strong whining, but mostly from the magnet on the Eneloop.
PWM at 18 kHz (4.8MHz CPU, divider 1, fuse 75) still produced a slight whining, hmm…

At 18kHz PWM values of 2 - 10 - 40 - 255 resulted in 12mA - 102mA - 198mA - 404mA with a single full and resting Eneloop. Keep in mind that this boost driver by design does not regulate anymore with 1 NiMH cell. See HKJ’s test for the Nanjg110, especially the first graph. So the current does degrade straight from the beginning in all modes. Results with 2 cells will be better for sure, but those later.

The 404mA at PWM 255 is about the same that resulted in driving the bare Nanjg110 on that LED, which I did before I hooked the setup together. So the FET with PWM does not seem to loose much energy here.

So far, so good.

Short version: nanjg 110 is boosting voltage fed to mcu and FET whose gate is pwm controlled by Attiny13A, correct? Could you use a BLF tiny10 DD (or any BLF DD) stacked on the 110 this way?

Short version: Yes, that’s what it does.

BLF DDs: I can’t say, I didn’t follow the development and specs of the DD/FET drivers. But in theory, if you isolate the needed parts and feed them with the 110’s output, perhaps.

So is your test (above) essentially a mockup of wight’s board, or is it a different design altogether? Could wight’s board be mostly populated by stripping a 110 and an AK47?

Basically my test is derived from wight’s idea.
But I went along the datasheet of the PAM2803, as it seems wight has somewhere along the path mixed up the PAM2803 and the PAM2805 (see my comment in post#23), which are not pin-compatible.
The Nanjg110 seems to have the PAM2803, as the board is designed after that datasheet.
So I took

- a Nanjg110

- a stripped AK47 (for ATtiny13A, Cout)

- added 1yF OffTimecap (but the standard STAR firmware values dont work and need to be tweaked)

  • added a IRLML0030TRPbF N-Channel MosFET
    and that was it.

In the meantime I tested the stock Nanjg110 with several other diodes and inductors with interesting results (gaining efficiency with 2 cells and gaining output with 1 cell). Got a last diode today, will post altogether in some days.

I’d be interested to know if there is a better FET that could be used.

Hmm Interesting. I might have to start playing around with this too.

Unfortunately I can’t help with Fet options, I’m a blind bat when it comes to reading spec sheets.

I am not sure but dont these things tend to overheat , anything over 1A the IC’s need to be thermally bonded to the pill… I used to have a bunch of constant current boost drivers for lasers and even for the 2.4a output two of them needed to be paralleled.

here’s a pictorial.

P.S: not my image.

We’re talking about 1A output here, not more.
The PAM2803 is specified for 0.75A output. The Nanjg110 is overdriven already with a lower sense resistor (R100 instead of “R127”) and puts out ~1A in 2AA config. But this seems to be safe ground.
I have several Nanjg110 in household use (bunch of silver L2m with 1AA, 2AA in MiniMaglites) and none of them has died yet.

Any chance of paralleling 2 boost circuits on one pcb and controlling them with one attiny 13A?

I hooked up the full setup (110, ak47, FET) with 2AA and got magic smoke from the PAM2803 :frowning:

The boost controller simply blew up. |(
It occured after one of the first mode changes, I’m not sure from which to which, it happened fast and unexpected to be honest. There seem to be some spikes…
It’s surely the controller that died, I just swapped this single component from a new 110 and everything is working again (with 1AA).

I’ll stick to 1AA for the moment unless anyone has a convincing idea what might be the cause and how to avoid this.

I found a nice diode for the job.

The stock SS14 is incredibly large while being not quite up to the job to boot (only rated for 1A while datasheet recommends 2A). As I looked for 2A diodes - all large as hell - I stumbled upon the BAT60A (datasheet).

Even rated 3A, only 370mV forward voltage, and SOD-323 package. It’s the teeny-tiny component on the right, where the cathode line uses up almost half the component. Oh, and the price… 10.5 ct.

I hooked it up in replacement and in the last days I drained 5x 1AA and 6x 2AA (Eneloops) on this driver, while monitoring input and output current. Works perfectly fine. Even increases output current in 1AA config and efficiency in 2AA config (needs a lower input current to reach the 920 mA). I’m truly impressed.

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^ Nice discovery. You're doing some real R&D. Thank you for reporting this.

EDIT: So far in my search pretty expensive with shipping. Best I've seen so far is on Ali for $1.06/each.

Wow, impressive indeed. So what’s the current parts list?

Found some at a good price here (50 for 4.95USD shipped). Thanks for the info again.

Boost converters in parallel to the same load don't work (unless they are the type that are meant to be synchronized).

Received my order of 50 BAT60A's yesterday. Won't have a chance to try them out until I wrap up my current project, but I'm excited about them. They're so small. Hard to believe they can handle 3 amps.

Thanks again for reporting your find HarleyQuin. :)

Thanks for the work on this driver guys, I do not have the background to be of any use but I sure would like to see this little 15mm boost driver come off the ground :-)

As djozz says. I appreciate the effort as well.