Other Parts Discussed in Thread: TLA2528
I have a design I am working on that uses the ADS7828 running Vdd at 5V. The I2C bus is pulled up to 3.3V. It seems to mostly work, but I am occasionally seeing some unexpected values returned from the ADC via I2C. I am concerned that the ADS7828 can't reliably detect a logical high (3.3V) on the I2C bus. According to the datasheet the minimum logic high input threshold is (Vdd * 0.7) which in my case Vdd is 5V which would mean the minimum threshold is 3.5V.
That said, how could the 3.3V I2C bus be working at all with this part powered by 5V? Could it work, but with very little margin?