PCA9306: PCA9306

For normal operation, EN must be connected REFB, and both must be connected to the higher supply with a 200 kΩ resistor. This biases the EN pin so that output voltages above REFA are clamped.

With EN connected directly to the lower supply, the translator will still work, but now voltages above about 1.2 V will be clamped, and the speed will be somewhat reduced. In your case, this does not matter because all lines have pull-up resistors, and I²C is not very fast to begin with.

Hi Shubham,

I agree with Clemens' statements here. Normal operation for level translation requires that EN must be connected to REFB and both must be pulled up to the higher supply voltage through 200k ohm resistor. This correctly sets the internal gate voltage of the passFETs on SDA/SCL channels, clamping voltages above REFA during high logic transitions or idle state of the i2c bus. 

With the current setup, EN is connected directly to the lower supply (1.8V), voltage translation will still work, but now voltages above ~1.2V will be clamped (assume ~0.6V = Vth of the internal passFET). Speed is reduced due to the lower voltage applied to the gates of the internal passFETs via the EN pin (1.8V vs. 2.4V). This usually doesn't effect the system setup since I2C operates at speeds <1MHz typically. For this application, I don't see an issue. 

Overall, the setup would work as presented in the schematic.

Regards,

Tyler

Connecting EN to 3.3 V would raise the clamping voltage to about 2.7 V, i.e., high-level signals from side B would not be properly translated.

Hi Shubham,

The I2C signals look good. I don't see any issues. Is this with EN = 1.8V or 3.3V? 

Best way to check if the device is working properly is to check I2C signals on both sides of the device (input / output). 

Regards,

Tyler