This is a continuation of this question.

In my board RTC I2C lines are pulled up to controller supply voltage and the controller supply voltage will be off when the system is off.

At that time also RTC will be powered from the super capacitor.

I understood that RTC clock will cause supercapacitor to discharge.

May I know will these I2C lines also cause supercapacitor to discharge when pull up voltage is zero?


1 Answer 1


I2C bus is pulled up by resistors to some voltage. No device can push out current, they are open-drain pins. Battery will not discharge through I2C bus pins.

Also it is an RTC, they are sort of expected to be battery powered while everything else around it is unpowered. Except for the push-pull clock output from the RTC.

  • \$\begingroup\$ Thank you. But when the system is off pull up voltage will be zero. May I know at that time pull up resistor is connected to GND. \$\endgroup\$
    – Confused
    Commented 2 days ago
  • 1
    \$\begingroup\$ @Confused I just answered that is not a problem, the battery will not discharge through I2C. \$\endgroup\$
    – Justme
    Commented 2 days ago

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.