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TCA9406: OE connected to VCCA

Michael Hagmann
Prodigy 100 points

Part Number: TCA9406

I am planning to use multiple TCA9406 devices to connect several independently powered I2C peripherals to a single I2C bus.

The intended configuration is as follows:
- VCCB is connected to an always-on 3.3 V supply.
- VCCA is connected to a switched 3.3 V supply, controlled by a MOSFET.
- OE is tied directly to VCCA (what is possible according to datasheet chapter 9.2)
- Multiple TCA9406 devices share the same I2C bus on their B-side.

According to the datasheet, the I2C ports are high-impedance when either VCCA or VCCB is at 0 V.

My question is: Could switching VCCA on or off while OE is connected to VCCA cause any glitches, spikes, or unintended LOW pulses on SDA or SCL on the B-side? 

In particular, I would like to know whether the power-up or power-down transition of VCCA of one TCA9406 could disturb ongoing I2C communication with other devices on the shared bus.

Is tying OE directly to VCCA possible for this application?

Thank you for your support.
Best regards

  • 0
    TI__Guru 65858 points

    Hi Michael,

    Michael Hagmann said:
    My question is: Could switching VCCA on or off while OE is connected to VCCA cause any glitches, spikes, or unintended LOW pulses on SDA or SCL on the B-side? 

    If the I2C bus is idle pulled up to VCCA while it ramps, then I suspect no glitches, spikes, or unintended low pulses to the B-side. 

    The OE and VCCA would ramp together, keeping the internal passFET's gate voltage = OE pin voltage. The device would remain high-z while VCCA is powering up. 

    If B-side were to start I2C communication during the power up of VCCA, then I could see logic low pulses occurring from side B to side A. 

    Michael Hagmann said:
    In particular, I would like to know whether the power-up or power-down transition of VCCA of one TCA9406 could disturb ongoing I2C communication with other devices on the shared bus.

    My ideal application scenario for this device is to have VCCA and VCCB up (in any order), then drive OE = H when you are ready to communicate across the level translator. 

    Regards,

    Tyler