PCA9306: Translate UP - Master at 5V, Slave at 3.3V

Intellectual 1145 points
Waqas Haque

Part Number: PCA9306

Hello,

In my design the I2C Master operates at 5V and the slave is at 3.3V. According to the datasheet, the Master must be connected to interface 1 (SCL1, SDA1 and VREF1).

Is there another part I can use to translate down from the Master 5V to Slave 3.3V?

Thanks!

 
Best regards,
Waqas Haque
Systems Engineer
High Speed Signal Conditioning - HSDC
Texas Instruments
Intellectual 1145 points
Waqas Haque
  • Expert 5925 points
    fhoude

    Hello Waque,

    The master doesn't have to be connected to the Ref1 side, it just typically is.  We never specifically call out that the master has to be on the SCL1/SDA1 side, if so please show me in the datasheet and I will correct it.  The part doesn't know who is the master and who the slave is.  It only needs to know the voltage levels.  Just swap the sides, like below:

    I do have a couple of questions for you.  Are you trying to buffer the signals, meaning trying to isolate the capacitive load on the bus, or are you just trying to do the translation?  If you have a small board and don't connect using wires or board to board connectors which cause larger capacitive loading on the bus, then the PCA9306 is the perfect choice.  If you have a larger capacitive load than you may want to look at a part like the TCA9517, which is a buffered part. 

    -Francis Houde

  • Intellectual 1145 points
    Waqas Haque

    In reply to fhoude:

    Hi Frances,

    Thanks for the response. In my application I am using an HDMI port. The I2C lines on the HDMI port connect to the I2C lines of our chip. Our chip can only support 3.3V whereas most HDMI devices require 5V. Therefore I need translation from the HDMI port - 5V down to 3.3V for our chip.

    In addition, since there is an actual HDMI port/connector in which an HDMI cable would plug in, I am assuming the capacitive loading would be too high for PCA9306?

    So basically I guess it is translation + buffering I need. Will TCA9517 be the optimum choice here?

     
    Best regards,
    Waqas Haque
    Systems Engineer
    High Speed Signal Conditioning - HSDC
    Texas Instruments
  • Expert 5925 points
    fhoude

    In reply to Waqas Haque:

    Hello Waqas,
    Do you have a block diagram of your system design which includes where the harness is? This is important because depending on the system configuration and if you need to meet the compliant testing you will have to try and get the A side of the TCA9517 toward the harness where the compliance testing is done.
    -Francis Houde

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