Suggestions for integrating Lipo charger into PCB - Page 1
Forum section: electronics / projects

author: dsg123456789
author_rank: Newbie
timestamp: August 28, 2021, 08:20:17 pm
content: Hey everyone,I’ve been working on bringing up my first very complex board, and I’ve ended up running into what feels like a roadblock. The boards themselves include isolated CAN, SPI ports & a high power buck controller to control ~100 RGB leds with high-side current sensing, a UART to control several servos, a half dozen shielded capacitive sensor ports, and an integrated 3S lithium battery charger IC and a protection IC. I’ve got everything working with RTOS drivers written, except for the battery ICs.Both the battery ICs are the smallest parts (the only QFNs I’m using), I think I’ve found a mistake or two in their schematics (shouldn’t be showstoppers, but definitely they could be better; turns out I'm grounding the protection IC on the wrong side of its colomb counter sense resistor), and worst of all, they’re really becoming a sticking point, in that I can’t bring up that portion of the board (I’ve only managed to establish communications with one chip, a MAX77960, while the MAX17320 doesn’t respond at all).The MAX77960 does respond to my read requests, but when I write new values to program it, the values I write only seem to persist in 2 of the configuration registers (the others go back to factory settings). The chip also gets hot to the touch with only a 300mA flowing through it, which is worrisome since I designed the board/chip to handle at least 6A. I’m guessing that it might be overheating due to a problem with my reflow; I've copied the reference design exactly.I’m assuming that these are pretty rare, specialty chips, and so I don’t think I’ll be able to get help in debugging them, and so now I’m thinking I need to redesign this part of my board to derisk it, since I’ve managed to get everything else operational.Do you have any ICs or circuits you could point me towards to solve this onboard power problem? I need to be able to charge & possibly protect a 3S lipo battery pack (the pack probably needs each cell in a different place, due to mechanical constraints). I need the charger to be integrated into the PCB, because once the device is assembled, it would be very, very inconvenient to require removing the cells to recharge them.Here’s the features I think I need:- 3S Lipo charger- 3S Lipo protector (overvoltage, undervoltage, thermal protection (ideally supporting 3 thermistors in order to sense each cell)) – this I feel like maybe could be changed to a much, much simpler circuit without any smarts or fancy current counting.- I need to be able to draw at least ~80mA while charging in order to power the microcontroller and a few other circuits that decide when it’s OK to start charging- Need to be able to disable charging functionality, even if power is applied to the charger- I have pretty limited routable space remaining, so the easiest thing would be to control with I2C (happy to use an additional microcontroller), although I could use the I2C as GPIO instead, and I could maybe squeeze a single analog input to the host microcontroller as well.- I have about 20x40mm board area I can reclaim from the MAX17320 and MAX77960.- In stock now (LOL)Thank you for your thoughts and advice on the highest-success-chance way to create this integrated battery pack!

author: tooki
author_rank: Super Contributor
timestamp: August 29, 2021, 03:24:00 pm
content: The component choices seem sound; it’s probably much less risky to get those working than to switch to something new. I’d suggest spending the money to buy the evaluation kits. Use those to get your configuration just right. Then transfer it to your board.

author: tooki
author_rank: Super Contributor
timestamp: August 29, 2021, 03:27:57 pm
content: BTW, the manual to the dev board says this:QuoteSounds to me like this could be why your configuration writes won’t “take”.

author: dsg123456789
author_rank: Newbie
timestamp: August 29, 2021, 09:34:05 pm
content: Quote from: tooki on August 29, 2021, 03:27:57 pmThat is a great catch. I was surprised when I searched the chip's datasheet and didn't see write protection registers (since those are standard on safety-related ICs like this), but I searched for "lock" and "protection", and I missed the "chgprot" register. I will see if this is the trick for this chipIf not, it looks like I'll be ordering some eval boards and snooping the exact bus transactions.