I have a prototype board incorporating the MP2672 to charge and balance a 2S 18650 pack, the board operates normally on battery power alone. External power for charging is applied via USB or 5V DC jack (through diodes to isolate from each other). I have found that when external power is removed I lose communication with the MP2672, which I think is due to the IN (pin 1) being fed from the external supply only. If this is the case, is there a recommended way to power the IC when the external supply is disconnected? Here is the schematic for reference:
What is your system voltage at? Would it be possible to power the i2c lines from Vsys? You may need a voltage divider to fit within the pins absolute values.
Thanks for your reply Vinh, I do have a 5V buck supply fed from VSys (and 3.3V LDO off that). I’d need to keep this isolated from the incoming power path so would something like this work do you think?:
I may have misunderstood your question. Are your i2c lines being pulled up by the external power source used by Vin? Or is the pull up voltage not affected by the external Vin?
The pull-ups are supplied from a 3.3V LDO which is supplied from VSYS, so this is always powered, but if the external USB supply is not connected I have no communication with the MP2672. I assume that’s because there is no supply to Vin without the external supply connected? The above OR-ing diodes would supply Vin all the time without back feeding the charge path.
That could work since VCC is powered by VIN. VCC is used to power control circuitry.
However, my concern would be for battery life and how much of it would get drained when idle.
Ok thanks Vinh,
This portion of the circuit controls power to the regulators so when the circuit is off current flow from batteries should be very small. As I’m only interested in communication with the MP2672 while the mcu is running that should be fine, I imagine if Vlim is out of range and there is no current supply into SW the current into IN should be very low even when the circuit is on… One way to find out I suppose