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?
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.
Yes, I tested the new board with I2C built in and it works the same way.
What can I do to the board to find the issue?
Catch the battery detection function on a scope. Upon power-up, monitor the voltage on the battery node. If you have a demo board, you can see an example of what it does: the LTC4162 will source/sink a small amount of current from the battery node. Normally, this will look like the battery node popping up to the float voltage when the LTC4162 sources current. In your case, something must be holding the battery node at a voltage.
I tested the board by turning on Vin and monitoring Vbat and I can see that Vbat starts with 0 V, then goes up to 2.3 V 2.9 V and stops at 4.2V. It takes about 2 seconds from 0 V to 4.2V. What does it mean?
Do you think that I have some resistance Vbat to ground? I measured 5.5 Mohms when its off.
I had a potential divider used for ADC chip but I tested without it and it is still the same. It still thinks that the battery is connected.
I don't have a demo board.
I tried removing Vbat capacitor and it is reading now 3V battery voltage but it still thinks that battery is connected.
Can you capture a plot of the BAT voltage during battery detection and send it here? You shouldn't need to remove the capacitor.
Please see the image below. It stays around 3V for 2.4 seconds.Battery was not connected. Vin is 8V and I turned it on and triggered Vbat rise.
Is the ~2 second event when VIN is plugged in? In other words, does VBAT immediately jump up to 3V when VIN is applied? Or is there some delay?
Can you check for a leakage path from VIN to the battery node? I only have the charger section of your schematic, so I can't see if there's another possible leakage path. Feel free to send your full schematic privately.
The battery node is also going too high. You are configured for 1 Li-Ion cell, right? That might be another indication that something is pulling up the battery node externally.
It takes about a second for Vbat to jump to 3V when I turn on Vin. Please see the screenshot attached. Green trace is Vin.
I sent you my full schematic privately. I tried by disconnecting R25 resistor and even cutting the tracks coming from the battery track except the track that goes to the charger IC. Vbat also goes to the programmer board but there is nothing connected to it. And I tried cutting that track anyway.
Yes, I configured it to be one cell and I can see that when I check the register 0x43.
Sometimes when I restart the power, I get Vin undervoltage error even though it reads Vin 8V. Do you have any idea why?
I wrote a library to read the registers:
The charger state is cc_cv_chargeThe charge status is Vin undervoltage activeThe limit alerts are okThe charger state alerts are okThe charge status is okThe system status is okThe battery voltage is 3.044345 VdcThe input voltage is 7.903657 VdcThe output voltage is 7.906299 VdcThe battery current is 78.95944 mAThe input current is 106.9637 mAThe die temperature is 25.59198 °C
Thanks and Regards,
These are strange problems that I've never seen before, probably caused by logic issues. Your schematic looks good but, after taking another look at the layout, I would guess that the cause is the routing and induced noise.
Take a look at the layout recommendations in the datasheet as well as the demo board layout and you'll notice that there is a lot that needs to be changed to get this to work right. I recommend you give it another shot and send it to me for review before going to fabrication. Feel free to copy the demo board layout as much as is applicable to your requirements.