Hi there,
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:
Hello peakeelectronicinnov,
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.
Regards,
Vinh Tran
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?:
Hello peakeelectronicinnov,
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?
Regards,
Vinh Tran
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.
Hello peakeelectronicsinnov,
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.
Regards,
Vinh Tran
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 
Hello there, and sorry for bumping the topic which is identical to mine.
As far as I understood from the messages above, The MP2672 core is not working if Vin in not supplied and I am totally ok with this: if the IC gets a NACK, easy peasy, the battery is not charging!
I’m working on a custom handeld system, which makes use of a MP2672 to charge the internal dual cell LiPo battery from an USB 5V when installed in the docking station. The “SYS” pin is used to drive a 3V3 LDO which power a MCU which communicates via I2C with the MP2672, configured in an “host controlled” mode, to ask for battery status.
330R resistors are placed between MP2672 and the bus in order to protect the bus itself, 1k8R pullups are tied to the 3V3 described above (also tried 10k with no differences). nACOK and nSTAT are also tied to 3V3 via two LEDs, for MCU direct readback.
The problem is that when external supply is removed the MP2672 appear to drain current from the DATA line (no problem on CLK line) preventing any use of the I2C bus, e.g. between the MCU and the I2C display installed on the same BUS/board.
We’ve actually take the workaround in setting the MP2672 in “Standalone mode”, mounting R18 below and removing R7, thus losing the possibility to communicate with it asking for battery status.
Am I doing something wrong? Thanks in advance for any answers.
