Well, sh*t… As it turns out, a DIY modification of the indicator LED color scheme might be a bit more difficult than I anticipated:
I was hoping the reassignment of LEDs would be possible by simply swapping some of the wires connecting the driver (BLF-LT1-A2) and switch PCBs. Or at worst case, swapping the SMD LEDs themselves on the switch PCB assembly. Plus if necessary, replacing the current limiting resistors. The datasheet of the powerbank IC also supported this theory.
Boy, was I wrong, though…
Here is the reverse-engineered schematic of the switch assy and its connections to the driver PCB:
The circled numbers denote the identically numbered wires between the driver and switch PCB
As you can see, the LEDs controlled by the PB controller are connected antiparallel to each other and driven sort of “differentially”. Which makes wire swapping not feasible.
What’s even worse, the blue and amber LEDs Sofirn chose are in fact not separate components. They are part of the same 0606-size duo-LED. (The green one on the other hand, is a plain 0603 single-color led.)
The different package sizes and the fact that the blue and amber LEDs are integrated means swapping the existing LEDs around is also out of the question.
At this point, the “easiest” option left is to buy new LEDs, 2 duo and 2 single with the colors you want, and replace the current ones with them. If you’re determined enough to do that, and you intend to use a hot air soldering iron for the removal part, be careful not to melt the tact switch (wall it off with Kapton tape or aluminium foil), as the clearances are awfully tiny here… If I were to go ahead with this mod, I think I’d just use 2 normal irons (or an SMD tweezer iron) instead, just to be safe.
Here are some examples of applicable replacements for the duo led:
https://uk.farnell.com/kingbright/kptb-1615surkcgkc/led-red-green-80-50mcd-smd/dp/2426238
https://uk.farnell.com/kingbright/kptb-1615esgc/led-red-green-7-12mcd-smd/dp/2426236
https://uk.farnell.com/lumex/sml-lx0606igc-tr/led-1-5mm-x-1-2mm-red-green-smd/dp/1789153
https://uk.farnell.com/dialight/598-8410-207cf/led-red-green-65-59mcd-633-570nm/dp/3548426
https://uk.farnell.com/w/search?led-colour=red-green&packaging=cuttape&st=150066
If you live in luckier parts of the world where the really big distributors (Digikey, Mouser, etc.) do not have absolutely ridiculous shipping fees, you might find more options.
Unfortunately, I am pretty much stuck with Farnell, and in the applicable package size, I found only the handful of LEDs above in their catalog.
Fun fact: the indicator LED driver configuration utilized in the LT1 is not documented at all in the IP5310 datasheet. Its 2-LED mode is supposed to drive the LEDs in a basic single ended configuration, with no series (current limiting) resistors, since the IP5310 itself has integrated current regulators:
So either Sofirn decided to use the driver “in a creative way”, or it is an intended, but undocumented feature of the IP5310, borrowed from its bigger brothers which support differential LED drive natively.
What I still cannot wrap my head around though is why the engineer at Sofirn chose to implement the LED drive this way in the first place. The usual argument for the differential approach is to save an extra wire (no dedicated GND needed).
Bun the LT1’s switch PCB needs a GND wire anyway for the switch and the green LED, so in our case the number of wires connecting the 2 PCBs were not reduced… It is also strange they went for the blue-and-amber duo LEDs, which are rather exotic, and I imagine more difficult and expensive to source, instead of the more ubiquitous red-and-green ones combined with standalone amber LEDs. I guess we’ll never know…
Anyway, happy modding!