[Oshpark] BLF SRK FET v3 (46mm / LFPAK56 / Dual+Triple Channel / ATtiny13A+85)

If you get rid of the FW need for an external voltage divider for LVP, you can just leave R1 unpopulated and use the current R2 pads to run an indicator LED off pin7.

Sorry, it’s fairly obvious, but I just thought of it so clearly I had to say something :face_with_monocle:

Would additional components on the board be needed/useful for an indicator LED off pin-7?

I haven’t used one yet, so my guess is you would take the R2-pads for a bleeder resistor. Connect the indicator LED to the MCU side of the bleeder resistor or the free pad on R1. What about the resistor in series before the LED (R5 on the Q8 board), not needed?

@TomE
Thx for the clarification on the 85/85V. Will order, can’t resist anymore

Just a small update.

I changed R1/R2 (still the build of post #1) to 330k/82k and that brought the current in off-state down to 11µA (0.011mA) with a cell that is 3.3V resting. With 33k/8k2 it had been ~68µA after the ADC_off() firmware mod. So in the end I’m down from ~200µA to 11µA which is very very good.
LVP is still working as before and triggering effectively at ~2.9V. But I’ll keep monitoring that. TomE, great help, the firmware changes made for the major part.

While at it I installed a 33R as series-gate-resistor (Rgate). Not sure if it’s needed, as the FET is not PWM’d, but it can’t hurt to have it in place.

HQ - just found out the LDO requirement is Vout on pin #5, not pin #3. That's an important spec, so I just found out. TA's LDO drivers are wired the same way. Think you got it from Richard's BLF SRK V2. Weird because Richard's other LDO drivers have Vout on pin #3. The LDO's I bought from Mouser, and one I got from Richard have Vout on pin#3, so of course there was smoke when I tested it . Fortunately the only thing that seem to smoke was the 4.7 ohm resistor, so easy to replace, but I have to wait on an order of LDO's with Vout on pin #5.

Thx for the hint, I’ll added a note to the partlist.

Vout on pin5 was to my knowledge the sole version here on BLF for the SOT-23-5. Mattaus used the LT1761 in his Knucklehead V3, wight proposed 4 different LDOs with the same pinout for his AxxDD-SO8+LDO and yes, RMM used it in the BLF SRK V2, I simply kept it so.

Such a pretty board… sometimes I come here just to look at it :wink:

It's also purty in the flesh, ahh, I mean FR-4 and copper, or whatever these things are made from . Wai'tn now for the LDO's.

Forgot bout that thread. The wrong LDO I bought Richard used in the TK61 driver he designed, listed in the OP here: https://budgetlightforum.com/t/-/31955

Figured it was well tested as he stated, so had to be a good one - PN# MC78LC50NTRG, spec here: http://www.mouser.com/ds/2/308/MC78LC00-D-110708.pdf

Again - this is the wrong one. Who knew?

Wait til you get a glimpse of her next sister :wink:

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@TomE, yes, that’s definitely a different LDO pinout on RMMs board. One can only guess why he changed to it, but at least layout did not dictate it.

Ohh - been working on this:

It's gonna drive this:

Firmware has been tested. It's Narsil as the baseline. The table of voltage levels have been updated to support the 360K/47K R1/R2. It comes straight out of the spreadsheet I used to calculate them. It's conditionally compiled in, as below. The calculated values work very well now. Found a bug in indexing these ADC values where indexing was off by one. Not sure, but thought I got this code from somewhere else, maybe Bistro?

#ifdef USING_360K
// The ADC values we expect for specific voltages: 4.4V to 8.8V (2.2v to 4.4v). This is
//  for using R1=360K/36K, R2=47K/4.7K, and direct connection from Batt+
//  to R1, no diode in-between, with an LDO and a 2S battery configuration.
#define ADC_44     236
#define ADC_43     230
#define ADC_42     225  // 100%
#define ADC_41     220
#define ADC_40     214  //  75%
#define ADC_39     209
#define ADC_38     203  //  50%
#define ADC_37     198
#define ADC_36     193
#define ADC_35     187  //  25%
#define ADC_34     182
#define ADC_33     177
#define ADC_32     171
#define ADC_31     166
#define ADC_30     161  //   0%
#define ADC_29     155
#define ADC_28     150
#define ADC_27     145
#define ADC_26     139
#define ADC_25     134
#define ADC_24     129
#define ADC_23     123
#define ADC_22     118
#endif

That driver used to be a lot roomier. :confounded:

:person_facepalming:

@TomE
now we know where the driver got to…
just borrowing your picture :innocent:

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I hope you can fix the 7135 issue. Even if DEL more or less had ruled out a thermal issue I will make the connection of Q1 to GND wider.

Any other ideas or needs for changes in your book?

That mod sounds good. Dunno bout anything else - I like all the versatility this driver offers. There's plenty of thru holes for Batt+, but I'd still like to do something more there, but not sure how. I'd like to be able to solder fill the thru holes but not sure if the holes are wide enough. Hard to see but the holes themselves appear to be covered in purple soldermask but I'd like to see the entire holes to be bare ENIG. This way solder filling should work well.

This is what I did for the contact surface:

Got from here: etsy.com brass-discs-20-gauge (might be cheaper direct from their shop: https://boppermetalsupply.com/) in 1 3/8" size that fit well. All I did was drill the center hole and sand it down to get it flat, then reflowed to the driver. Bad thing was I added the brass disc only after reflowing the parts, so didn't get the PCB heated enough to use hot air, so had to use a torch.

Brass is preferred (to me at least) because it's harder than copper and I don't think has as much problems for electrically conduction loss from oxidation.

The thru holes seem to have filled up with rosin and not solder paste unfortunately. If I were to do this again, I'd apply solder paste maybe on the component side and apply the heat on the battery side to see if I could fill the holes first, before reflowing the copper disc.

From the picture above, clearly the larger ground thru holes are not coated with soldermask. I didn't closely look at the Batt+ thru holes though - I might be wrong there.

What is the rationale for calculating R1 and R2 in cases like a 12V SMPS input source, instead of battery cell(s)?

Huh? Dunno wut the heck a 12V SMPS source is. If you don't need LVP on it though, then you should disable the LVP in the code.

Well, i meant a wall adapter 6V or 12V or a battery, whichever the LED works with.

So i wonder what changes are required on the circuit, a different LDO for example, and also in the code. Btw, do you mean “low voltage programming” by LVP?

Low Voltage Protection - the firmware logic to read the voltage level, and act on it accordingly if it's deemed to be getting low. We typically use two thresholds - one for a warning, and to drop output amps, then the next threshold to turn off LED output completely in order to save the cell from going below it's "safe" level. The two levels can be 3.2/3.0V or 3.0/2.8V.

Well, the board I built/shown in post #51 above has 2S (2 in series) Li-Ion input, so it gets from 6.0V to 8.4V input. It uses this LDO: https://www.arrow.com/en/products/mic5235-5.0ym5-tr/microchip-technology that supports up to 24V input, and outputs 5V, so it can handle a 6V or 12V DC source. If you want LVP, then the R1/R2 voltage divider resistors would have to be picked accordingly, and the ADC values to match - listed this all in post #51 for the 2S setup. This design though passes the source voltage along to the LED(s) - it doesn't buck or boost voltage to the LED(s).

Thank you for the explanations. Also, is this driver really capable of driving 16 x XP-G2? I’m guessing the max. current is solely dependant on the FET.

I'm using 16 XHP50's so it's a lot more power than 16 XP-G2's. The FET I chose, the SIR404DP is capable, but I'm having problems with the 7135. I added a grnd jumper to help in heat, and added a heat sync on top of the chip, and it's surviving now, but not working normally - delays coming on, sometimes doesn't come on at all.

Don't have time to trouble-shoot it further now. Might get back to it, or eliminate the 7135 altogether