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PCA9306: PCA9306 as translator+switch and switch only

Yash Mulgaonkar
Prodigy 20 points
Part Number: PCA9306

Tool/software:

Hello folks,
We want to use the PCA9306 as a switched translator and as a switch only.

Will these work? The datasheet isn't very clear on the use of the EN line with an MCU.

What changes if any would you suggest?

Thank you!

Application 1:
Translator + Switch.

VREF1 = 1.8V, VREF2 = 3.3V, EN = 3.3V GPIO

EN is controlled with a 0-3.3V MCU GPIO. Weak pull down added to keep PCA9306 off at power up.

Application 2:
Switch only:

VREF1 = 3.3V, VREF2 = 3.3V, EN = 3.3V GPIO

EN is controlled with a 0-3.3V MCU GPIO. Weak pull down added to keep PCA9306 off at power up.

  • 0
    TI__Mastermind 47448 points

    Hi Yash,

    The switch and translation configurations are shown in the datasheet: 

    In switch configuration, for VCC1 = VCC2 = 3.3V, EN <= 3.3V + VTH. EN<= ~3.9V. 

    Yash Mulgaonkar said:
    Application 1:
    Translator + Switch.

    The application that you have shown will not work correctly. EN will be 1.5V higher than VREF1. EN is only allowed to be a threshold voltage above VREF1. EN <= 1.8V + 0.7V = 2.5V. 

    Since EN = 3.3V or 0V, the in the 3.3V case from the ESP32, the PassFET connecting side 1 to side 2 will always be ON which means a voltage divider would occur. Translation would not work properly here. 

    Yash Mulgaonkar said:
    Application 2:
    Switch only:

    Application 2 looks valid, given that there are PU resistors on SCL2 and SDA2. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 20 points

     

    EN <= VREF2+Vth, not VREF1+Vth
    What am I missing?

  • 0 in reply to Yash Mulgaonkar
    TI__Mastermind 47448 points

    Hi Yash,

    The LSF architecture is similar to PCA9306. We can use this figure for comparison: 

    In the switch mode, if side 1 = 1.8V, side 2 = 3.3V, and if the voltage applied to the EN pin varies from 0V to 3.3V, in the case where EN  = 3.3V, the passFET connecting side 1 to side 2 is always ON. Therefore you get a voltage divider between 3.3V to the 1.8V side through the PU resistors on both sides of the translator. 

    In order for voltage translation to work the EN voltage needs to be <= 1.8V + Vth in order for the internal passFET to be off.

    A possible solution for application 1 is to follow the voltage translation mode use case in the datasheet, remove the 10k PD resistor, and use an open-drain output from the ESP32 device on the EN to control when the PCA9306 should be high-z. 

    Regards,

    Tyler