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PCA9306 - VREF1 / VREF2

Other Parts Discussed in Thread: PCA9306


we are using the device PCA9306 as i2c level shifter to communicate between a 3,3V Master and a 5V Slave. Both sides of the SCL and SDA Pins were pulled up to VREF1 / VREF2 by using 1,8k resistors.

Unfortunately we mixed the VREF pins - so the 3,3V Master is connected to VREF2 and the 5V Slave is connected to VREF1.

Most of the time the device as well as the i2c communication works well, but under some circumstances, the device gets damaged.
Could the wrong connection of the VREF pins be the reason for this?

Best Regards,


  • Hi Patrick,
    If VREF1 (5V) is larger than VREF2 (3.3V) then the VREF1 pin can be tied to the Enable pin, and pulled up to 5 V using 200kohm resistor. The EN pin should be tied to the larger voltage supply. Is this a possibility?
    You are seeing damages on the device in the configuration because the terminal voltages on the transistor are exceeding 5.5V which is the recommended max on the terminals. This can result in extra leakage current. Can you list under what circumstances you see the damage (high temperature)?

    So to summarize the damage is due to the incorrect connection. if possible I recommend changing the connection on the board to match the datasheet, or tie the EN pin to the VREF1 pin.

  • I flagged this problem to the Ultimaker team after my PCA9306 blew up 3 times in total on two of my Ulticontroller v2.1 boards...

  • Hi,

    Thank you very much for your information.
    It`s not possible to list under what circumstances we see the damages cause they aren`t comprehensible at all. We made a lot of tests under different circumstances (temperature, over voltage, etc.) within the last days running the products in 24/7 mode. No product gets damaged in our scenario.

    At the moment I´m thinking about having an ESD discharge problem on the customer side - could this also be a possibility?

    Anyway, we will have to redesign the layout to meet the datasheet.

    Best Regards,
  • Hi Patrick,

    I too am eager to find out exactly why the PCA9306 keeps blowing up, whereas in the original Ultimaker (3D printers) setup, this does not seem to happen.

    The Ulticontroller has VREF1/VREF2 mixed up exactly as you mentioned, and given the date and your dutch sounding name, I assumed you were from the Ultimaker team. My mistake (besides, the values of the pullup resistors and the Master/Slave roles are not the same as you mention in the Ulticontroller design).

    If you take a look at I added my setup at the bottom of that thread.

    The first time my chip blew up, I believe it must have been from ESD, because I made the beginners mistake of not insulating the rotary encoder's shaft from by massive aluminium control knob. The very moment I touched the knob, there was a discharge, and my controller went dark instantly, with the PCA9306 smoked.

    However, the problem reoccured after I replaced the chip and after I insulated the shaft from the knob. This also happened after I tried a new Ulticontroller board.

    Since my 3d printer has a full metal (aluminum) frame, and that frame is grounded, I can't see how ESD is now affecting my system. Surely any discharge would be routed through the frame to ground this time?

    The Ultimaker team is looking into it, and suggested that I use the original setup (i.e. the "official" power supply instead of my self-sourced SMPS). They also

    suggested that I NOT ground the frame, and that I measure the VREF1, VREF2 voltages on oscilloscope at power on and power off to see if somehow they come on out of sequence (whatever that means, I didn't find any timing requirement for VREF1 and VREF2). Also, they suggest I measure the24V DC output of my switching power supply to see if any excessive transients occur during power on/off.

    I would appreciate to learn about your findings too when you get to the bottom of this...

    Thanks and good luck!