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

    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 managed to break the pads and connect I2C to micro.

    I've got the values below.

    I'm still not sure what is wrong with my board. Could you please check the values? The charge status indicates that there is a fault but it doesn't say what fault. The voltage readings are correct. 

    Is there anything else I could read?

    Thank you!

    Regards,

    Emilija

    0x34 charger_state cc_cv_charge = 64 constant current constant voltage charge
    0x35 charge_status ilim_reg_active = 32 Interrupt request that causes an ilim_reg_active_alert SMBALERT upon ilim_reg_active
    (VCSP-VCSN greater than 45mV). May indicates that the switching regulator is currently
    controlling power delivery based on a safety current limit. This should not occur under
    normal conditions and is likely the result of a circuit board fault. Alternately indicates
    that the switching regulator is in dropout (near 100% duty cycle) and is not regulating
    on any feedback control loop.
    0x36 LIMIT_ALERTS_REG 0
    0x37 CHARGER_STATE_
    ALERTS_REG
    0
    0x38 CHARGE_STATUS_
    ALERTS_REG
    0
    0x39 SYSTEM_STATUS_
    REG
    327 "0000000101000111"
    0x3a vbat 18409 3.5418916
    0x3b vin 4848 7.994352
    0x3C vout 4828 7.980684
    0x3d ibat 11 0.000016126
    0x3e iin 190 0.00027854
    0x3f die_temp 13503 25.9145
    0x40 thermistor_voltage 10905 9982.607104 RNTCBIAS = 10000
    0x41 bsr 0
    0x42 jeita_region 3
    0x43 chem_cells_reg 4593 "0001000111110001" ?
    0x44 icharge_dac 31 ?
    0x45 vcharge_dac 31 4.2
    0x46 iin_limit_dac 63 1.185185185 27mr
    0x47 vbat_filt 18398 3.5397752
    0x48 bsr_charge_current 0
    0x4a telemetry_status_reg 1
    0x4b input_undervoltage_dac 53 7.59375
  • 0
    •  Analog Employees 
    on May 3, 2019 2:51 PM in reply to emilija.zuk

    Hi Emilija,

    Good info, thanks. Here's some info on ilim_reg_active (more info in the alert description than elsewhere):

    You should inspect the connections around that sense resistor. Perhaps one of the sense lines was cut or not connected properly on that particular PCB.

    Regards,
    Zack

  • 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 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

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