Q
I am using ADG3304 to buffer between a 3.3V processor and a 1.8V I2C
peripheral. It works OK
but it does not like the I2C state when momentarily no one is driving the data
line.
Is it suitable for I2C?
A
The ADG3304 could work for I2C but it will not 100% meet I2C specifications
because of its totem pole output stages.
In answer to a previous customer , our ADG330x factory applications engineer
wrote :
“The ADG3308 was designed to drive capacitive loads, so the current driving
capability of its output stage is not significant.
The output impedance is about 6K and this values can be used to calculate the
output voltage for resistive loads.
Also, the architecture used by the output stage is totem-pole which is not
fully compliant with the I2C standard that requires open drain/collector
outputs.
In conclusion, the restriction on resistive loads (pull-up or pull-down
resistors) is on the minimum value due to the limited current driving
capability and not on the maximum load resistance.
For a given resistive load by using the 6K value for the ADG3308 output
impedance you should be able to calculate the output voltages for each logic
level and check if it is within the specifications required by the application.”
(NOTE: our ADG Engineer was referring here to ADG3308 but the same applies to
the 4 channel version, ADG3304).
