I am developing a wireless device composed of :
- 2 Varta CP 1654 A3 Li-Ion 3.7V 120mAh (supporting 2C charge) with protection circuit module
- 2 MCUs that can handle Li-ion CC/CV charging
My wireless device is composed of 2 earbuds connected with a cable, I can't use any other type of battery. There is a Protection Circuit Module (PCM) on the board where each cell is mounted in each earbuds (PCM recommended by Varta).
Correct me if I'm wrong but fast charging at 2*2C of parallel cells seems to be problematic for this reason:
If during charge cell_A reaches 4.2V before cell_B, cell_B could either receive a dangerous current > 2C if PCM_A triggers overcharge or ultimately both PCM_A and PCM_B would prevent the charging.
My GOAL is to have the fastest charging device possible while being safe and the fact that I have two ICs able to manage CC/CV charging makes me wonder if I could trigger switches between the batteries when the device is connected (Vcharge available) so then I could manage a 2C fast charge independently for each cell :
I am trying to find a circuit that could act as a switch between the two cells. I thought at first about two MOSFETs in parallel but the body diodes will prevent the use that I want.
LOGIC_A represents if Vcharge is available to the device
The switch should be closed when no charge and open during charge.
I know this is unusual and most designs have single cell battery while some others have parallel batteries but with slower charging current than 2*2C. Please my question is not about modifying the design of my product, I just want to know if there is the possibility of such a "switch" circuit that could allow me to use the two chargers at fast charge instead of just one at slower charge.