Please help me as I'm stuck!
I use LTC4162-L to charge a lithium battery and it works great!. I had a few prototype boards and every time I solder it myself. I've been having issues with the latest boards and the design and layout is the same as previous ones! It gives an output but it doesn't charge the battery. I tried resoldering a few boards multiple times but still haven't fixed it. Sometimes charging turns on but it turns off next time I plug in.
I took the good working board and non charging board and swapped all the components one by one and still good working board worked meaning that there wasn't a component issue.
I tried measuring the voltages around the IC to spot the difference and I noticed that pin 11 is 1.01V for a good working board and pin 11 oscillates from 0V to 2.4V slowly maybe once per second. What does it mean?
What are the other reasons for this IC not to charge? I use it standalone design without a micro so I can't debug it. Maybe its a thermal issue, I'm not sure.
I resoldered it multiple times now and its the same issue. The output still works even when I plug in the battery. Its just doesn't charge. I had a few times charging while testing so its not like it doesn't work all the time. Also the battery I'm using is low so it should charge. I also tried leaving it for like half an hour.
When you say that you swapped all components, do you mean all components besides the LTC4162? If that's the case, I would assume that the non-working unit has been damaged somehow and I would suspect that replacing it with a fresh unit would fix what you are seeing.
The RT pin should not be oscillating like that for any reason. Is there a valid resistor on it?
Yes, I swapped all the components including the LTC4261!
Yes, I have a correct resistor fitted 93.1K. And the exactly same resistor was fitted on the other board.
I'm going to try a few more times to solder the IC on because I still think its a soldering issue. Maybe my soldering technique is wrong:
I place the solder paste and the IC. Then I use a hot air set to 210°C. Then I use a soldering iron set to 350°C and go through the long pads to get rid of shorts. My old technique was to just to remove the access soldering with a wick and now I found it easier just to go through with a soldering iron. My old board still works using the new technique.
I might try the exactly same components I have on a good working board to transfer them to the fresh new board.
Another option is to design a PCB that connects IC to the micro so I could actually read what's going wrong.
Please suggest any other ideas.
Also I noticed that sometimes it started charging once I soldered a component for example RT pin resistor on. Then it stopped charging once I unplug the the battery and plug again. Maybe because it was still warm after the soldering and then it cooled down.
I have two 10K resistors fitted for the NTC pins and I measured the resistances.
I made sure the RT resistor is soldered properly.
I will send you my schematic and layout to check. I'm sure its okay because it worked. All other circuitry on the board are off. I have two DC-DC converters not far from the charger circuit but they are off.
Just a quick update.
I tried by physically removing all the components from the non-working board that not part of the charging circuit and didn't help.
I tried swapping the ICs again with a working board and still working board works and non-working board doesn't charge.
Perhaps the PCB has been overworked. Interestingly, the problem seems to follow the board and not the IC, so it sounds like a problem with the board.
I might recommend that you do use the solderwick and clean the IC's footprint with alcohol before trying to re-solder. After cleaning it, inspect for any damaged or shorted pads.
Your general soldering procedure sounds good since you are able to solder reliably onto one of the boards.
For your next design, I recommend you put some test points or a header footprint on DVCC, SDA, SCL, and GND. You should also put footprints for pull-up resistors from SDA/SCL to DVCC. You don't need to populate these footprints on your final design, but it won't cost you anything to just add them and they will help for debugging.