Hello,
We are using the super capacitor charging IC BQ24640RVAR to provide the power back up of our system when power off and for that we are using IC Part#BQ24640RVAR to charge the super capacitor - 4 in series with 100F/2.7V each. Input voltage of the IC will be around 25V to 26V and super capacitor will be charged up to 10V. We have used the boost converter to convert the 26V from 10V, used the boost converter IC Part#LM3478MAX/NOPB. Due to lack of pins in board to board connector, we have used the I2C I/O expander to contol the IC BQ24640RVAR pins for chrging enable, power good and stat. I2C is connected with the Master MCU.
There is no isuue with the super capacitor charging and the boost converte in normal condition. In some condition we found issues, below we have mentioned the one of the condition for the issue,
After fully charged the super capacitor, if we cut off the main power, the capacitor will discharge to generate the 26V to run the system. If we turn on the main power before the super capacitor completely discharge then,
- I2C pin either CLK or DATA will damage at MCU side (the pin will short with GND)
- Also the 3.3V pin of the MCU is short with GND.
I have also attached the schematic for your reference.
Kindly provide your suggestion to resolve the issue at earliest.
