LTC4162-L charging issue

Hello,

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.

Thanks!

Regards,

Emilija

Parents
  • 0
    •  Analog Employees 
    on Apr 30, 2019 2:32 PM over 1 year ago

    Hi Emilija,

    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?

    Regards,

    Zack

  • Hi Zack,

    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.

    Regards,

    Emilija

  • 0
    •  Analog Employees 
    on May 13, 2019 3:07 PM over 1 year ago in reply to emilija.zuk

    Hi Emilija,

    Can you capture a plot of the BAT voltage during battery detection and send it here? You shouldn't need to remove the capacitor.

    Regards,

    Zack

  • Hi Zack,

    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.

    Thank you.

    Regards,

    Emilija

  • 0
    •  Analog Employees 
    on May 14, 2019 3:01 PM over 1 year ago in reply to emilija.zuk

    Hi Emilija,

    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.

    Regards,

    Zack

  • Hi Zack,

    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.

    Thanks.

    Regards,

    Emilija

  • Hi Zack,

    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_charge
    The charge status is Vin undervoltage active
    The limit alerts are ok
    The charger state alerts are ok
    The charge status is ok
    The system status is ok
    The battery voltage is 3.044345 Vdc
    The input voltage is 7.903657 Vdc
    The output voltage is 7.906299 Vdc
    The battery current is 78.95944 mA
    The input current is 106.9637 mA
    The die temperature is 25.59198 °C

    Thanks and Regards,

    Emilija

Reply
  • Hi Zack,

    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_charge
    The charge status is Vin undervoltage active
    The limit alerts are ok
    The charger state alerts are ok
    The charge status is ok
    The system status is ok
    The battery voltage is 3.044345 Vdc
    The input voltage is 7.903657 Vdc
    The output voltage is 7.906299 Vdc
    The battery current is 78.95944 mA
    The input current is 106.9637 mA
    The die temperature is 25.59198 °C

    Thanks and Regards,

    Emilija

Children
  • 0
    •  Analog Employees 
    on May 17, 2019 2:26 PM over 1 year ago in reply to emilija.zuk

    Hi Emilija,

    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.

    Regards,

    Zack

  • Hi Zack,

    Yeah, I suspect layout issue again.

    I sent you my current layout. I compared my layout with demo board and I can see that mosfets are further away from the IC. I don't have enough space on my board. Also C15 Vbat capacitor is 90° and maybe C17 is further away from my board. The rest of it looks similar. 

    Do you think these layout differences could cause an issue? 

    Datasheet highlights that Vout capacitor needs to be close to the IC and I fixed that issue. Maybe its not happy with a battery capacitor now.

    Thanks.

    Regards,

    Emilija

  • 0
    •  Analog Employees 
    on May 20, 2019 3:08 PM over 1 year ago in reply to emilija.zuk

    Hi Emilija,

    It looks much better, no problem with the FETs being closer.

    This is a 2-layer board, right? The grounding makes me nervous because there is a lot of routing on the bottom of the PCB which cuts off the IC's GND paddle reference and creates longer paths for the circuitry. There is a GND pour on layer 2, right?

    For all power connections, I recommend you via down to your GND pour for the GND connections. Feel free to connect direct to the IC paddle through grounded pins on layer 1 (like your routing of the bat capacitor's GND through the SYNC pin, that's good, but a via to the GND plane will help as well.

    C17 needs a via that goes directly back to the IC paddle through the pour on layer 2.

    Take another look for these techniques on the demo board layout and copy where you can. Also double-check the grounding. I'd like to see a version of the layout with the pour visible.

    Regards,

    Zack

  • Hi Zack,

    I sent you my current layout that battery detection doesn't work. Yes, it is a 2 layer board with a ground pour.

    I will try and improve it and send you a new layout.


    Sorry I meant C11 before. Why does C17 need a via if its on the top layer?

    Thanks.

    Regards,

    Emilija

  • Hi Zack,

    I sent you my updated layout. Please have a look.

    I tried investigating by placing the capacitor Vbat C15 further and closer to the IC but didn't help. It only made a difference when I removed it. Then the battery voltage was 3V but still didn't detect the missing battery.

    I also tried changing the switching frequency to see if it changes anything but it didn't make a any difference.

    Do you think that I need to change it to 4 layer board?

    Thanks.

    Regards,

    Emilija