Confirmation of LTC4120 battery charging part

Hello, 

I am using LTC4120 for my wireless battery charging system. I want to confirm whether it is charging the battery but I do not know how to confirm it. I have got only 900mV as Vbat when Vin is 15V.  I have checked the circuit on LTspice and it works, but not the actual circuit.  

Please help me to confirm whether it charges a battery.

This is the picture of LTspice simulations. 

  • 0
    •  Analog Employees 
    on Oct 13, 2020 9:38 PM 1 month ago

    Hi, 

    Did you just test with DC on VIN or did you use a wireless transmitter? 

    It seems like you are trying to set a 4.8V float charge voltage at BAT. When you test it, is it possible to check the SW node waveform and the PROG pin voltage? 

    And is it possible to share your layout?

    Thanks!

  • Dear Wenwei, 

    I am trying to test it with direct DC voltage to VIN without a wireless transmitter. 

    I got 4V (DC) at SW, no voltage at PROG pin. I have attached pictures of the SW node of the oscilloscope and circuit on the breadboard.

  • 0
    •  Analog Employees 
    on Oct 22, 2020 6:36 PM 1 month ago in reply to Nyamaa

    Hi,

    It is strange to see 4V DC on SW pin with 15V input voltage and 900mV at output of a buck converter. When there is no switching signal, both FET of the buck converter should be off, and you should see 900mV at SW node, as the inductor will have low DC impedance. Could you please check the connection of the inductor?

    Thanks,

    Wenwei. 

  • Dear Wenwei,

    Thank you for your comment.

    I checked the connection of the inductor and it has no problem. 

    I have other questions: 

       1. What is a bad battery fault state? 

       2. After 26 min, CHRG and Fault pins indicate a "bad battery fault" state. They indicate "charging state" until 26 min with Vprog=0V and Vsw=4V (DC). When it is " a bad battery fault" state, Vsw is 0V.

    [Vin=18V, INTVcc=4.2V, Vfb=3V, Rprog=3k, Rfb1=1M, Rfb2=1.4M, Lsw=20uH]

    What is the problem? Why is it happening? 

    Many thanks.

  • 0
    •  Analog Employees 
    on Oct 23, 2020 2:58 PM 1 month ago in reply to Nyamaa

    Hi, 

    If the battery remains below the trickle charge threshold for more than 30 minutes, charging terminates and the fault status pin is asserted to indicate a bad battery.

    I do not understand why Vbatt is measured 900mV while Vsw is at 4V DC. Where is the 3.1V voltage drop? 

    One possible reason for the part not working correctly is that the input cap not placed closed enough with shortest route. We see customers having this issue before. 

    INTVcc cap also needs to be placed correctly for the part to work correctly. 

    Thanks,

    Wenwei.