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PCA9306: Power sequence

Liren He
Prodigy 120 points
Part Number: PCA9306

Hi TI experts,

We've one question about the PCA9306.

We adopt P1V8 for Vref1 and P3V3 for Vref2 and Enable pin. And from the datasheet, the Vref1 is connected to the core power-supply. But in our board, P3V3 is early than P1V8, so are there any influence to the I2C bus? 

  • 0
    TI__Guru 62920 points
    Hi Liren,

    While there is no issue related to the PCA9306 itself, both power supplies need to be fully powered for I2C communication to work. If VREF2 is high while VREF1 is still low, the device will be enabled (since the enable control is referenced to VREF2) but see a low input on the other side. This low input will propagate to the VREF2 side, holding the bus low until VREF1 ramps up.

    If I2C communication is needed on the VREF2 side before VREF1 powers up, you might want to use the circuit shown in Figure 8 of the datasheet. That would allow the enable control to be held low for some time at start-up.

    Max
  • 0 in reply to Miguel Robertson
    Prodigy 120 points
    Got it, thank you for your support!!!