Michael Predko

Question on actual I2C pin wiring for an MC9S08QG8

Discussion created by Michael Predko on Jan 17, 2011
Latest reply on Jan 25, 2011 by Michael Predko

Hey Folks,


Hopefully a quick one.  I am planning on using a MC9S08QG8 for power management implementing a boost supply from alkaline/NiMH batteries to 5V and then back down to 3.3V via a buck topology for a 32 bit MCU (CF or Kinetis) as well as allowing the 32 bit MCU to communicate with the '08GQ8 via I2C. 


Will there be problems if the '08QG8 is running on battery power (potentially as low as 2.2V) if the I2C pull ups are on 3.3V?  Really what I am asking is are there ESD protection diodes on the '08QG8 pins that will cause a current flow from the pull ups that are always enabled? 


I guess the simpler/best solution would be to power the I2C pull ups from the battery source (the same source as the '08QG8) correct?