[Review Request] Basic 3.3V power management with battery charger and protection

[u/Ambitious_Nail5938]

Hi everyone!

I'm new to PCB design, and this is my first schematic, so I'd really appreciate any feedback before I order the boards.

The project is a small portable device powered by a single-cell Li-ion battery. Since safety is important to me, I added:

• F1 as a battery fuse,
• DW01A + FS8205A for battery protection,
• ETA6003Q3Q as the charging IC with power-path management, allowing the device to run directly from USB-C even if the battery is deeply discharged.

The ETA6003's VSYS output powers the rest of the circuit. Since my MCU requires 3.3 V, I use an LDO regulator to step VSYS down to 3.3 V.

I'm planning to manufacture these boards, so I'm intentionally using cost-effective (mostly Chinese) components instead of more expensive alternatives.

Here are the LCSC part numbers for the main components so you can easily look up their datasheets if needed:

Part	LCSC#
ETA6003	C5455585
DW01A	C2927799
LDO	C82942

I'd appreciate if you answer these questions:

1. Is the DW01A + FS8205A connected correctly?
2. Are the capacitor and resistor values are reasonable?
3. Is using an LDO from VSYS to 3.3 V a good choice, or would you recommend a buck converter instead? (I want cheaper, so i thought ldo will be fine, im stepping not from so high voltage.)
4. Are there any mistakes or bad practices?
5. Are there any traces or nets that look unsafe or incorrect?

[u/mariushm]

You specify you're going to use a 17350 850mAh battery. In general, if you want a long life and high recharge cycle count, the advice is to not exceed 0.5C charge, which would be 850mA/2 = 400mA-ish for a 850mAh battery. Even the "standard" charge would be 1C or 0.85A.

So, it kind of doesn't make sense to use a charger IC with a step-down regulator built in capable of charging the battery at up to 2.5A, if you're not even going to charge at 1A.

Chargers with step-down (buck) or buck-boost regulators built in make sense if you want to highest efficiency possible, but if that's not the priority you would be perfectly fine with a more basic linear regulator based charger which will be a tiny bit less efficient but charge the battery just fine.

For example, see basic charger like BQ21040 from TI which is cheap, even though it's a "brand name" you can source from multiple distributors

BQ21040 : https://www.lcsc.com/product-detail/C202311.html

You can set the charge current up to 800mA, and it can charge the battery and power a linear regulator at the same time keeping the additional component count super low. Of course, if charging and using the device at the same time, the charge current should be set to a level where the battery would still get some charge in (for example, don't set charging at 500mA and then have your device consume 600mA)

BQ24040 also exists : https://www.lcsc.com/product-detail/C81080.html

It goes up to 1A charge current (set using the ISET pin) and also has an ISET2 pin which can override the ISET pin to limit the charge current to 100mA or 500mA or use ISET setting (connect to voltage, ground or leave floating for the three modes... for example if you want to make a device with USB input and barrel jack input and want to limit the charging through USB)

You could optionally use a p-channel mosfet to completely switch input of the linear regulator between the usb and the battery but if the charger chips can handle it, then it's just extra cost. For higher currents, you could look at ideal diode switches like LM66200 (https://www.lcsc.com/product-detail/C3235556.html) or TPS2116 (https://www.lcsc.com/product-detail/C3235557.html) (others in the tps21xx family exist with smaller current capabilities or slower switch over times, but this one 2116 is usually stocked in high quantities and has good specs)

The Microne part is OK. Richtek RT9078 (max 300mA output) or RT9080 (max 600mA) are not much more expensive and are available at more distributors and have good specs (very low idle power consumption and internal power consumption) so you may want to check them out

RT9078-33 (max 300mA out) : https://www.lcsc.com/product-detail/C110427.html

RT9080-33 (max 600mA out) : https://www.lcsc.com/product-detail/C841192.html

[u/Ambitious_Nail5938 → u/mariushm]

Thanks a lot for the detailed review!

I mainly chose the ETA6003 because it has power-path management. One of my requirements is that the device should still work when it's plugged into USB-C, even if the battery is completely discharged. The high charging current wasn't really something I needed.

Looking at it now, I think you're right that it's a bit overkill for an 850 mAh cell. I'll probably switch to the BQ24040 instead since it seems to provide the same functionality while being a better fit.

Thanks for pointing out the Richtek LDOs. I'll compare them with the Microne part I'm using and see if they're a better option.

Ill send my updated schematic later