I'm currently working on a custom PCB where I have a microcontroller hooked up to 3 LiIon batteries which are meant to get charged by a CN3722 IC. However, when I connect a solar panel to the circuit the batteries are not getting charged. The datasheet of the CN3722 can be found here.
Some more information:
- All three LiIon batteries have a voltage of 4V so they should be getting charged.
- One has to specify what the battery regulation voltage is supposed to be. This is done with a resistor divider. The formula is Vreg = 2.416 * (1 + (R22 / R23)), in my case this equals to roughly 12.6V.
- You also have to specify the MPPT voltage (since its not real MPPT). The formula for this is Vmppt = 1.04 * (1 + (R17 / R18)). I wanted to be able to adjust this in the finished PCB so R17 is an adjustable resistor in my case. At the moment I have set it to 150k Ohm in order to have the MPPT voltage set to roughly 16V.
- A charging cycle should basically start, if...
- Vin rises above the battery voltage and
- Vin is no less than the MPPT voltage set by the resistor divider.
My problem is that it doesn't charge. I have measured the current draw from the solar panel and I only measure ~6mA under pretty much full sunlight. This is due to the "CHARGE" LED being lit. However it is not charging. I don't know why though. I designed everything like it is described in the datasheet and tried to take all PCB layout considerations into account.
This is my schematic: (typical application circuit can be found on page 2 in the datasheet)
The Vsolar net is connected to an INA219 IC, which basically just measures the charging current so I can monitor it.
This is the rather small INA219 circuit:
As you can see its simply measuring current/voltage. I don't think this might cause any problems, can it? The VCC net is directly connected to the positive of the battery.
Finally I will attach a few images of my PCB. Even though I don't think I made huge layout mistakes I could miss something. This is the complete PCB, which contains some circuits I haven't mentioned (like a 3.3V buck converter.), because they are not related to this problem.
I know this is a rather extensive question, but I would really appreciate any help.