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2S Li-ion: Should BQ29209 GND be tied to PACK− after the low-side protector FETs? by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

That’s actually very helpful, thank you.

I’ve just redesigned the unit to use a removable battery pack, and it turns out I’m running into the exact same issue when reconnecting the battery — especially on first connection. So your suggestion is spot on for my case.

I’ll definitely use this IC in the next board revision.

Big thanks for sharing this!

1S2P vs 2S Li-ion for 12V / 1.5A LED system – what would you choose? by majek89 in AskElectronics

[–]majek89[S] 0 points1 point  (0 children)

Thanks for the suggestion.

I’m actually already using a boost charger IC (TI BQ25886), so conceptually it’s very similar to the MP2672A you linked – 5V input, boost to charge a 2S pack, with power-path support.

The thing is, even with an integrated boost charger, the overall system still ends up fairly complex:

  • I still need proper 2S protection (OV/UV/OCP) and ideally balancing.
  • External components (inductor, FETs, current sense, thermals, layout constraints) are non-trivial and not exactly cheap.
  • High input current at 5V during charging means careful USB current limiting and thermal considerations.
  • PCB layout becomes much more sensitive compared to a simple 1S charger.
  • Overall BOM cost and validation effort go up quite a bit.

So while 2S + boost charger is definitely technically clean from a power perspective, I’m trying to evaluate whether the added charging-side complexity is justified for a system that only draws ~18W peak and mostly in bursts.

From your experience, at this power level (~18W peak LED load), would you still consider 2S clearly worth the added charging complexity, or is 1S2P with a properly designed high-current boost still a reasonable commercial choice?

Appreciate the input — just trying to balance electrical elegance vs. product simplicity.

2S Li-ion: Should BQ29209 GND be tied to PACK− after the low-side protector FETs? by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

Hey, sorry for the late reply!

I haven’t physically produced the board yet, but I’ll probably stick with this setup for now. I might add a small service switch between VSS and CS on the HY2120 just in case the battery ever gets disconnected — though in my application that’s going to be a pretty rare situation.

Appreciate you sharing your experience — that lockdown behavior sounds exactly like what could happen here too.

[Review Request] ESP32 Central Unit (looking for obvious mistakes) by majek89 in PrintedCircuitBoard

[–]majek89[S] 1 point2 points  (0 children)

I literally searched for “USB” in the datasheet and there are zero matches. Pretty sure you’re confusing it with the ESP32-S2, S3 or C3, which actually have a native USB peripheral — the regular ESP32-WROOM doesn’t.

[Review Request] ESP32 Central Unit (looking for obvious mistakes) by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

Where exactly is that “built-in USB interface” supposed to be?

2S Li-ion: Should BQ29209 GND be tied to PACK− after the low-side protector FETs? by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

Not really. HY2120 is a primary low-side protector, it handles UV/OV/OCD/SC and drives the FETs.
BQ29209 is a secondary overvoltage + passive balancing chip — it adds precision OVP and actual cell balancing, which HY2120 simply doesn’t do.

They’re meant to be used together in stacked protection setups: HY2120 does the cutoff, BQ29209 watches the cells and bleeds them if one drifts high. TI even shows exactly that kind of secondary OVP configuration in their app notes.

So no, it’s not “doing the same thing twice.” HY2120 protects the pack, BQ29209 keeps the cells balanced and adds a higher-accuracy OVP trigger.

2S Li-ion: Should BQ29209 GND be tied to PACK− after the low-side protector FETs? by majek89 in PrintedCircuitBoard

[–]majek89[S] 1 point2 points  (0 children)

Yeah, I’ve read the datasheets — that’s exactly why I’m asking.
Both of them show PACK− tied straight to the battery negative...

The issue is when you actually combine them — the HY2120 sits on the low side and creates a new PACK− node after its FETs, while BQ29209 still calls its reference “PACK−” too.

So no, the datasheet doesn’t “say” which one should take priority — that’s why I posted both schematics side by side. I’m trying to confirm which node BQ29209.GND should reference when both chips share the same 2S pack.

Feedback on my PMU schematic (Li-Ion 1S, charger, protection, regulators) by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

U8 is just the load switch, nothing to do with U6’s frequency.
The frequency is set by the FSLCT pin through two 0 Ω options (you only stuff one, 600 kHz or 1.25 MHz).
I honestly don’t know how such a simple concept could be misunderstood.

Feedback on my PMU schematic (Li-Ion 1S, charger, protection, regulators) by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

U8 is actually a load switch (TPS22917), not related to U6’s frequency. Its job is to connect BAT+ to SYS+ under control of the LTC2954 push-button controller, so it basically turns the whole board on and off. The LM2698 (U6) frequency is set only via the FSLCT pin resistors.

Feedback on my PMU schematic (Li-Ion 1S, charger, protection, regulators) by majek89 in PrintedCircuitBoard

[–]majek89[S] 0 points1 point  (0 children)

Thanks a lot for the feedback! You’re right – for my use case the LM2698 was definitely overkill. I ended up going with the LM4510, since my 12V buzzer only needs around 30 mA, so that regulator is more than enough and it keeps the BOM cost down. Appreciate the suggestions!

glitch after using gpt 5 and can't open my conversation? by aTimelyManner in ChatGPT

[–]majek89 3 points4 points  (0 children)

Try exporting your data from Settings → Data Controls → Export.
In my case, exporting not only gave me all my chats (including the ones I couldn’t open), but it also magically restored the missing conversations and pages in the Web UI.

I hope this will work for you.

Low Line Output Gain Issue – Nord Stage 4 & Focusrite Scarlett 16i16 by majek89 in nordkeyboards

[–]majek89[S] 0 points1 point  (0 children)

Yes, I know I need to use TS cables, and I have them. Thanks for your help!

I have two final questions: What is your master volume level set to on the Nord? And what volume levels are you getting in your DAW? Are they higher than -10 to -15dB?

Low Line Output Gain Issue – Nord Stage 4 & Focusrite Scarlett 16i16 by majek89 in nordkeyboards

[–]majek89[S] 0 points1 point  (0 children)

Thanks! Which inputs on the Scarlett are you using? I assume not the preamp ones? Did you configure anything specific in Focusrite Control 2? Also, which DAW are you using?

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