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Original question:

TCA39306-Q1: Enable voltage level

TCA39306-Q1: Is it suitable for 1.8V on both side, each 1V8 may power off or power on?

Shan Huang
Prodigy 30 points
Part Number: TCA39306-Q1
Other Parts Discussed in Thread: TXS0102-Q1, SN74LVC2G66, TCA39306, SN74LVC2G66-Q1, TS5A3166-Q1

Hi Team

I am looking for a 1V8 I2C isolator chip to isolate two 1.8V power domain (I2C resistor pullup to) for automotive application.

Voltage on both side may be un-powered separately.  I2C speed is FM+.

There isn't a requirement of GPIO control. If any power is absent, I2C is disconnected and no current leakage will happen.

Is TCA39306-Q1 suitable for this scenario?

Thank you.

  • 0
    Guru 266830 points

    There is no isolation between the Vrefs; this device is not suitable.

    You would need a translator like the TXS0102-Q1.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    Hi Clemens

    Thank you for reply.

    TXS0102-Q1 is 1.65 V to 3.6 V on A port and 2.3 V to 5.5 V on B.  VCCB can't be 1.8V.

    If circuit changes to as below, Vref1 and Vref2 use VCC2, is it works for isolation?

    Thanks!

  • +1 in reply to Shan Huang
    Guru 266830 points

    When VCC2 is up, the two sides are connected to each other. You could replace the TCA with two wires.

    I would recommend a simple switch like the SN74LVC2G66, but it needs to stay powered, and a control signal.

  • +1 in reply to Shan Huang
    TI__Guru 55950 points

    Hi Shan,

    For the TCA39306-Q1 device, in your configuration when Vref1/Vref2 are GND, side 1 and side 2 are HIGH-Z. With how TCA39306 is designed though, if Vref1 is GND and Vref2 side is powered, there will be some leakage current from Vref2 into Vref1 during that case. 

    For a switch solution I will reassign the thread to the subject matter expert if you have questions or want a different suggestion (please let us know if Clemen's suggestion works for you or not.)

    -Bobby

  • +1 in reply to BOBBY
    TI__Mastermind 26313 points

    Thanks for looping me in Bobby!

    Hey Shan,

    If you're just looking to isolated the I2C bus, Clemens suggestions is a good one here and will work. The SN4LVC2G66 has an automotive version as well (SN74LVC2G66-Q1). It will be able to support the voltage and frequencies for FM+ I2C. As Clemens also mentioned though, you'll need to keep the device powered up. 
    If you're also looking for a solution in which the VCC would be powered down occasionally with the 1V8 I2C signals may be present still at the I/O's, your best bet would be 2x TS5A3166-Q1

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 30 points

    Thanks, Rami, Bobby and Clemens.

    I think your suggestions are workable. But recently , I found that diode PI4ULS5V202Q can translate I2C between 1.8V on both side and has 2Mbps speed.

    I prefer to try PI4ULS5V202Q at first.   

    Thank you