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TM4C1294NCPDT: Is SDA and SCL pin 5V tolerant?

David Chance
Genius 4775 points
Part Number: TM4C1294NCPDT

I understand TM4C1294's GPIO pins are not 5V tolerant except USB (I learnt the hard lesson from burning the chip by allowing 5V to connect to digital inputs)

Since a lot of I2C designs are in 5V, I wonder if the SDA and SCL are "semi 5V tolerant" (SDA and SCL are both open drain/collector so the 5V is just a pull up to 5V)? If so, what kind of pull up is recommended for 5V operation?

Thanks!

  • 0
    TI__Guru 72500 points
    The pins are not 5V tolerant. There is a diode between the pin and the 3.3V supply. This will clamp the high SDA and SCL levels to roughly Vio+0.3V. The input clamp current needs to be limited to 2mA or less. That 2mA limit also applies if the I2C bus is powered before the microcontroller. In that case the pull-ups need to be 2.5K or more. The other devices on the I2C bus need to be content with a 3.3V high level.
  • 0 in reply to Bob Crosby
    TI__Guru 72500 points
    The normal solution in this case is to use pull-ups attached to 3.3V. Most 5V I2C devices see 3.3V as a valid high.