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.
Any ideas what's gone wrong?
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…
The BSR test will only be run if you tell it to run and a "good" BSR reading is not a gating requirement for charging to start. BSR should be irrelevant here.
It works if you put…
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?
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.
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?
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?
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.