I want to connect an AVR (ATmega48PA) to an I2C bus whose pullups are connected to 2.8V which is the operating voltage for other devices on the bus. The AVR is running at 3.3V.
Since SDA and SCL pins are open drain, the AVR, if connected, isn't going to "push" 3.3V on the bus, so other devices on the bus are safe. Also, as per the electrical characteristics section of the datasheet, the threshold for logic high is 0.6*Vcc which comes to 1.98V for when Vcc is 3.3V. The I2C bus voltage is well above this threshold so I guess I can connect the AVR directly to the bus without any level shifting. Is that correct?
Datasheet Page 383, Table 33-2 : Common DC Characteristics