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PCA9306: Behavior During Partial Power On

TI_USER
Prodigy 30 points
Part Number: PCA9306

In the implementation shown in datasheet Figure 9-1, if the 3.3V supply is ON and the 1.8V supply is OFF, will SCL1 & SDA1 be high impedance? 

  • 0
    TI__Mastermind 47748 points

    No. Powered off-high impedance can't be true here because VREF1 will drop to 0V, causing the voltage on the EN pin to shift to 3.3V instead of 1.8V + VTH. 

    Because of this, the internal FETs will be biased because the gate voltage set by the EN pin will be 3.3V, and the input side will be 0V due to pull-up resistors pulled up to the 1.8V supply which is now 0V. 

    side 1 will be connect to side 2 due to VGS > VTH. I expect both sides to be pulled LOW in this scenario if significant leakage to GND occurs on SCL1/SDA1. 

    Regards,

    Tyler