LIPO charger for Arduino 3.3V Pro Micro - Page 1
Forum section: electronics / general

author: Peabody
author_rank: Super Contributor
timestamp: February 12, 2019, 06:43:52 pm
content: In response to a question over on the Arduino forums, I worked up a simple 1S LIPO charger for the 3.3V Pro Micro. Schematic attached. The circuit is set up for "load sharing", which allows the USB V+ rail to power both the Micro and the charger independently so charging will proceed to shutdown while the Micro is doing its thing. Or, if USB power isn't connected, the battery will take over and supply power to the regulator.If anyone sees a problem with the circuit, please let me know. Otherwise, not having a Micro at hand, I wonder if there is a convenient place to connect to the USB V+ line (UVCC in the Micro schematic). Is it practical to solder a wire for the charge circuit to the high side of the fuse so the charging current will not be limited by the fuse? If not, what would you think about removing the fuse? My Mini clones don't have such a fuse. Not sure about the other models. But I would think the computer or whatever that's driving USB has protection against a short, and wonder if the fuse is really of any benefit.Thanks

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 12, 2019, 07:31:18 pm
content: The switching setup looks right. That's pretty much what I do as well when I include charging circuits (unless they already have this integrated, often called "powerpath").A couple remarks:* The fuse F1 should be put directly between VBUS1 and UVCC. As it is on your schematic, the "charger module" bypasses F1 for no good reason (that I can see anyway).* Not sure what there is exactly on this "charger module" besides the TP4056. I don't know what the link between 'OUT+' and the + of the battery is. Is there any extra circuitry or ar they internally connected?* Use a low leakage diode for D2 preferably (reverse current) to avoid unnecessary leakage current (flowing due to the body diode of the PMOS) from the battery to the charger circuit when USB is not plugged.

author: Peabody
author_rank: Super Contributor
timestamp: February 12, 2019, 09:51:31 pm
content: Thanks very much for your comments.Quote from: SiliconWizard on February 12, 2019, 07:31:18 pmI was just thinking that if the charger current has to go through the fuse, then that current would have to be limited to a few hundred milliamps, which might lead to extended charging times - depending of course on the battery size selected. And as I said, I'm not sure that any other Arduino models have such a fuse, particularly the clones. In any case, if the charging current is to go through the fuse, then the place to connect is at jumper SJ1 where there is a nice pad available for use (making sure not to bridge the jumper, which has to stay open).QuoteThe module comes in two versions - with and without the DW01A protection circuitry - and both have various caps and charging indicator LEDs. I'll attach a pic of the one with protection. The OUT+ and battery + terminal are indeed directly connected. The protection circuit operates via the negative rails, so OUT- and battery negative are not directly connected. The module without protection would just have two outputs, plus and minus.QuoteWell, when USB is not connected, the entire mosfet will be fully ON, so the body diode's characteristics won't matter. But reverse leakage through D2 certainly can matter. However, the D2 diode is part of the Micro, not something added by the charging circuit. So it is what it is, leakage-wise. I asked the guy on the other forum to disconnect USB, power his Micro by applying 5V to the RAW pin, connect a 100K resistor from the SJ1 jumper pad to ground, and measure the voltage at the pad. He got 0.01V. I think that means D2 doesn't leak very much. I don't know if that means it's a standard diode, or that it's a low-leakage shottky. But I think 0.01V is not going to cause any problems. For anyone's D2 that leaks more, the only solution is to reduce the value of the gate resistor to 47K or whatever it takes to eliminate the problem.