BQ29732 li-ion protection circuit does not output correctly - Page 1
Forum section: electronics / projects

author: VEGETA
author_rank: Super Contributor
timestamp: May 26, 2023, 11:12:14 am
content: Hello,I have developed a circuit for a certain use, which includes BQ29732 protection IC in it. please see it in attachment.The circuit does not connect the output when I plug the battery. I need to connect GND and Pack- briefly or connect COUT DOUT to Vpack+ or something like that.when not working, I read 2.9v between the sources of the 2 protection mosfets or simply between the battery negative and total circuit ground.when i touch the protection mosfet pins it works, but when i remove the battery and quickly insert it again it does not work and i have to re-touch.I tried understanding what the problem is but couldn't, everything seems as intended in datasheet and evaluation module docs.Here are more measurements when I plug the battery and circuit does not work:DOUT to Vss = 0v.COUT to Vss = 2.9vGND to Vss (Vpack- in drawing) = 2.9vbattery voltage = 3.9vVBatt for protection IC = 3.9vV- from protection IC to Vss = 2.9vfor your kind help.this is a product I want to sell and has nice market for it. I hoped it will work but this happened after changing the design a lot and thinking a lot.best regardsDatasheets for used parts:Dual mosfet packageprotection ic

author: Peabody
author_rank: Super Contributor
timestamp: May 26, 2023, 05:26:44 pm
content: I have no experience with that chip, but that behavior may be a "feature". It may be necessary to apply external charging power to the system to wake it up. I think the theory is that you can ship products with the batteries installed, but they won't be active unless you first apply external power to the system. This maximizes shelf life.

author: VEGETA
author_rank: Super Contributor
timestamp: May 26, 2023, 06:50:36 pm
content: Quote from: Peabody on May 26, 2023, 05:26:44 pmi need to understand this from datasheet.you mean charging power to what pin exactly? I have a charger circuitry there but not active due to i am away from my lab now and can't do stuff as i like.the design of this board requires it to work without charger connected, it will be a mod board for a game console in order to provide power to internal cmos clock circuit to keep time since its an old system and its circuit relies on very bad battery...etc ... this is a solution to that.when console is on, charger circuit is on and will deliver power and charge to Vpack+ and to battery. now protection ic should have been on the "on" status and battery is connected to the LDO which will deliver the final power to system's internal cmos clock circuit.when console is off, the battery + LDO should be on to deliver power without any disconnection.is it clear now?is there a design flaw that i have done to cause this behavior?any IC that can fix it?

author: VEGETA
author_rank: Super Contributor
timestamp: May 26, 2023, 07:11:33 pm
content: OMFG I just read the "NORMAL" operating mode as this:Quoteand there is this note directly beneath it:Quoteso this note says it all!!! don't u think so?!so the only thing I need to verify is to connect a charger which cannot be when I am out of the lab, need 2 days.I just tried to hook battery + itself as the charger circuit input but didn't work as expected. so i do need an external charger.if so, then the user must plug the battery then when installing the board inside the console, he just needs to power the console for say 5 seconds and the board will still active forever... correct?

author: VEGETA
author_rank: Super Contributor
timestamp: May 26, 2023, 09:10:18 pm
content: I soldered a usb 5v cable to charger supply as it will be the case in final application, and it worked as intended! thanks for opening my eyes on this.

author: Peabody
author_rank: Super Contributor
timestamp: May 26, 2023, 10:52:06 pm
content: Quote from: VEGETA on May 26, 2023, 07:11:33 pmI think so. As long as he doesn't disconnect the battery, then once it is all working, he should be able to connect and disconnect the console power, and the battery will remain enabled. At least that's my understanding of how these things work.

author: VEGETA
author_rank: Super Contributor
timestamp: May 26, 2023, 11:24:06 pm
content: Quote from: Peabody on May 26, 2023, 10:52:06 pmwell, yes.now i confirmed this by disconnecting the charger and it is been working for over 1 hour now, this should be unloaded state where in the console it will be loaded. load is very very small though, in the nano amp or so range.i just don't want it to lose charge fast. I am using a crappy chinese battery and here is the current readings:[time -> volts]Charging:12:03 -> 3.97312:13 -> 4.033so it charges fairly quickly for 100 mA setting. it could really reach full charge each playing time.discharging:12:19 -> 3.98212:39 -> 3.97112:56 -> 3.96701:38 -> 3.96302:13 -> 3.96102:25 -> 3.96103:01 -> 3.96003:43 -> 3.95905:02 -> 3.958next day PM12:02 -> 3.956DISCHARGING 2:started at 18:20 when 4.158v18:38 -> 4.14619:13 -> 4.13502:57 -> 4.10903:53 -> 4.10813:11 -> 4.104as mentioned, this is unloaded. so quiescent currents of chips + maybe the self discharge of the cell.i noticed it quickly reduced to some level then settled on it. I am no expert in 18650 batteries so i don't know if this is normal behavior.