4015 not starting the charge process

Hi folks,

I've got a new LTC4015 design that is not charging the 4S1P LiFePO4 battery at all.  I've designed the max charging current to be 12A. I have it set to LiFePO4 Standard Charge = CHEM0 = H, CHEM1 = Z.  Number of cells = 4, CELLS1 & 2 = L, CELLS0 = Z.  I'm using the default register values.  I haven't hooked up the I2C port.

Here are some of the measurements:

Vin = 15.66V

UVCLFB = 1.902V

INTVcc = 4.935V

NTC = 0.075V

Batsens = 12.37V

INFET = 17.40V

OUTFET = 15.6V

TG = 12.44V

BG = 0V  <-------- is this the problem?

I think I have the schematic designed correctly as I tried to follow the demo board's design as closely as I could.

PDF

Any ideas what's gone wrong?

Thanks,

Richard

  • I need to add some additional info:

    The charging does start but only if I put an ammeter in series with the battery lead.  And then only if I connect the meter's lead to the uA/mA input and turn the dial to the uA position.  The charging will not start if I have it connected to the 10A input on the meter.

    I put a 10 ohm resistor in series with the2.2uf  2P5Vcc cap.  Doesn't make any difference in the behavior.

    Has anyone ever seen this sort of behavior before?

    Thanks,

    Richard

  • 0
    •  Analog Employees 
    on Jun 26, 2020 7:05 PM 1 month ago

    Hi Richard,

    Your schematic looks fine. Usually, the issue here is the layout. Here's a quick guide that shows you what to look for with your layout. The demo board layout is a good reference and you should be sure to follow the PCB layout recommendations in the datasheet.

    DOCX

    Regards,

    Zack

  • Thanks Zach,

    I might have to re-spin the PCB as my current design is only 2 layers.

    Did you see my comment that the chip will start the charging process if I insert an ammeter in between the battery and the positive terminal on my board?  Do you think that points to a bad layout?

    Thanks,

    Richard

  • Hi Zach,

    I did re-do the board layout so now I have vias to ground under the 4015 chip.  This iteration has a 10 ohm resistor in series with the 2.2uf cap from 2P5Vcc to ground.  It still will not charge the 1S4P LiFePO4 battery pack unless I put the current meter in series with the positive lead of the battery pack.

    I've connected the I2C port and here are some of the register values:

    Charger_State = 100000000 = bit#8 => charger suspended

    System_Status = 0000 0010 11000 0111, DRVcc = OK, INTVcc = OK, Vin = OK, OK to charge

    Vbat = 0x3F65 => 12.48V. My meter measured as 12.53V

    BSR  (register 0x41) = 0x00 <<<<<<<<< What causes this to be zero?

    So, is the BSR value the reason the chip is in suspended mode?

    Thanks, 

    Richard

  • R12 = 10 ohms and C9 = 2.2uF.  Is C9 close enough?

    here's the bottom side of the 2 sided board:

    The design is in Kicad and I'm happy to send you the files if that will help.

    Thanks,

    Richard