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

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  • 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

  • Hi Zack,

    I found what the issue was. I moved Vout capacitor closer to the pins by soldering directly on long pads I had and it is charging now!

    I had long pads and components a bit further away to make soldering easier. I didn't expect this IC is so sensitive to layout. But it works now and we starting using I2C which is great to read voltages and currents.

    Can you please tell me the accuracy of the voltage reading? At the moment we use ADS1115 to read the voltages.

    Thank you.

    Regards,

    Emilija

  • 0
    •  Analog Employees 
    on May 7, 2019 3:22 PM over 1 year ago in reply to emilija.zuk

    Hi Emilija,

    That's great. Comparatively, it is not so sensitive to layout, but all switchers are to an extent.

    For the ADC accuracy, refer to the Telemetry A/D Measurement Subsystem section of the spec table (page 5).

    Regards,

    Zack

  • Hi Zack,

    I have another question please.

    Why do I get cc_cv_charge and constant voltage for a charger state when the battery is not connected?

    I would expect to get bat_missing_fault and charger_off states.

    I measured 4.25V where the battery supposed to be fitted but its not fitted.

    Thanks!

    Regards,

    Emilija

  • 0
    •  Analog Employees 
    on May 8, 2019 9:00 PM over 1 year ago in reply to emilija.zuk

    Hi Emilija,

    If there is no battery installed when VIN is applied, you should see the bat_missing_fault. However, if the battery is removed after it has already been detected, the charger has no way of knowing this. From the charger's perspective, it just stops pulling current and that causes the charge voltage to pop up to the target charge voltage. The charger will go into CV mode as you are seeing now.

    If you were to toggle suspend_charger it would go back to battery detection and realize that the battery is missing. If you are using a battery with a thermistor, you can use that connection to determine whether it is present or not.

    Regards,

    Zack

  • Hi Zack,

    I tried restarting the IC and it still thinks that the battery is connected. Also it reads 4.2V sometimes 4.3V.

    Do you think I have an issue with my design?

    I use 10k resistors instead of thermistor.

    Thanks.

    Regards,

    Emilija

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