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TCA9803: TCA9803 level shift for one master and two-slave

Ben Chen75
Prodigy 250 points
Part Number: TCA9803
Other Parts Discussed in Thread: TXS0102, TCA9543A

Hello,

I am designing an application which need to shift 2.5V signal/clk from MCU to two slave devices with 1.8V (VCC).

I also need to disable one of the slave device while the other slave device is working. Can you advise how to

use TCA9803 and TXS0102 in this application?

Best Regards,

David

  • 0
    Guru 243180 points

    The TXS makes all I/Os high impedance when disabled, so you would need to add external pull-up resistors. The TCA980x always keeps the current source enabled.

    A simpler way to switch between two slaves would be a single TCA9543A.

  • 0 in reply to Clemens Ladisch
    TI__Guru 60042 points

    Clemens,

    Thanks for the help as always.

    David,

    Please let us know if you have any other questions.

    Regards,

  • 0 in reply to Clemens Ladisch
    Prodigy 250 points

    Hi Clemens,

    Thanks for your kindly reply. It seems TCA9543A can be used as a level shifter for I2C devices, but it dosen't have 

    a feature of bus disabling in my application. Ignoring the feature of bus disabling, should I bridge the master and 

    slave devices in the following scheme? I found the following paragraph from data sheet of TCA9543A.

    Best Regards,

    David

  • 0 in reply to Ben Chen75
    Guru 243180 points

    What exactly do you mean with "bus disabling", and "bridge"?

    The switch's VCC should be the lowest supply, i.e., 1.8 V. And the bus segment between the master and the switch also needs pullups.

  • 0 in reply to Clemens Ladisch
    Prodigy 250 points

    Hi Clemens,

    In response to your question:

    1. What exactly do you mean with "bus disabling", and "bridge"? ==> The slave devices are I2C like bus (2-wire MIPI-RFFE 2.1 interfaces). They have

        same device ID.  Thus, the Master (MCU) must disable one of them and only allow one active device at the same time.

        ==> The "bridge" means level translation between 2.5V buses and 1.8V buses.

    2. The switch's VCC should be the lowest supply, i.e., 1.8 V. And the bus segment between the master and the switch also needs pullups.

        ==> Do you mean that I need to pull up the data/clock buses on master side to 2.5V as well as pulling up those on slave side to 1.8V?

    Best Regards,

    David

  • 0 in reply to Ben Chen75
    Guru 243180 points

    The TCA9543A can be programmed over I²C to disable any of the slave buses. (If those I²C accesses conflict with the MIPI-RFFE devices, then the TCA9543A cannot be used.)

    On all three bus segments, pull-up resistors are needed to set the high-level voltage. (The pull-ups of all enabled segments work in parallel, so make the resistors twice as large as in a 'normal' bus.)