CN3722 is not working - Page 1
Forum section: electronics / beginners

author: aakash dey
author_rank: Contributor
timestamp: February 02, 2019, 07:35:34 am
content: I want to charge a 2-cell Li-ion battery with CN3722 charging IC. According to my circuit design, the float voltage at the battery terminal should be 8.4V. But, the float voltage is measured as 13.44V when input is of 15V. Also, when I connect the battery,it draws 220mA current for 1 second and after that it goes to 0A. Any idea, why this charging circuit is behaving like this?

author: ebastler
author_rank: Super Contributor
timestamp: February 02, 2019, 08:03:26 am
content: Have you produced a PCB from your (Eagle?) schematic, or hand-wired the circuit?If you created a PCB, it cannot work because your schematic is missing many junctions. (Two wires meeting does not mean that they are connected. You need to place a "dot" at the connection point. If you use Eagle's "net" function to draw connections, it should place those juntions automatically, but you can also add them manually via the "junction" tool. Please use Eagle's ERC = Electrical Rule Check and look at the results carefully, to check for missing connections and other errors in drawing the schematic.)If you hand-wired the circuit, have you checked very carefully that you have indeed made all connections, and don't have any unintended shorts? I would venture a bet that you will find some error(s) when you look again!

author: aakash dey
author_rank: Contributor
timestamp: February 02, 2019, 09:18:31 am
content: But, I have checked the schematic connection and also checked the brd file. I am attaching the brd file. You can easily understand from this. Please check the brd file.

author: ebastler
author_rank: Super Contributor
timestamp: February 02, 2019, 12:29:41 pm
content: The layout looks a bit awkward, but you are right, the connections seem to be there. (At least at first glance, and to the extent the screenshot lets me see them.)What program did you use -- is it indeed Eagle? Did you draw additional traces manually to make all connections? I can't understand why Eagle would know about the connections without the junctions in the schematic.How did you produce the PCB? Did you etch it yourself, or have it made by a PCB manufacturer? In either case, have you checked for unwanted shorts between the copper traces? Some of the distances seem awfully narrow, especially between the IC4 pads.

author: tsman
author_rank: Frequent Contributor
timestamp: February 02, 2019, 12:53:46 pm
content: What is R10 on PGND for? That isn't in the typical application circuit in the datasheet.

author: ebastler
author_rank: Super Contributor
timestamp: February 02, 2019, 01:09:46 pm
content: Quote from: tsman on February 02, 2019, 12:53:46 pmJust a 0 Ohm jumper, it seems; whatever it's meant for.I had a quick look and this seems to be a direct implementation of the manufacturer's recommended application circuit. Hence my initial focus on things that might have gone wrong in actually building the circuit.

author: tsman
author_rank: Frequent Contributor
timestamp: February 02, 2019, 01:45:44 pm
content: Quote from: ebastler on February 02, 2019, 01:09:46 pmOops. Yes. They had 0 ohm on their schematic. Not sure how I kept missing that.Quote from: ebastler on February 02, 2019, 01:09:46 pmYeah. Looks like it matches to me as well. The fixed value components look correct.

author: aakash dey
author_rank: Contributor
timestamp: February 04, 2019, 04:55:41 am
content: Yes, I have itched my circuit and checked the possibility of short, found nothing. Connections are ok. What could be the mistake??The 0R resistance is just for avoiding direct connections between power GND and system GND. But, no matter. I have checked also by removing 0R and connecting them directly( as per as datasheet). Still not Charging.In datasheet the recommended MOSFETs have VDSS=30V. But i have used SI4401, whose VDSS= 40V. Could it be a reason for not working of this circuit?