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PCA9306: Multiple devices enable with 1 GPIO

Joe DiBartolomeo
Expert 3115 points
Part Number: PCA9306

All, a  large customer would like to enable 16 PCA9306 with the same GPIO.

Using figure 9.2 as the base, Vref=1.2V and Vref2=3.3V, GPIO is 3.3V.

Is it as simple as connecting all EN together? how much drive current is needed from the GPIO, does the 200K resistor need to be changed, do I need 16 resistors?

Thanks,

Regards,

Joe

  • 0
    Guru 316780 points

    Each PCA9306 requires its own resistor.

    The worst-case estimated current is 16 × (3.3 V − 1.2 V) / 200 kΩ = 168 µA.

  • 0
    TI__Guru 72981 points

    Hi Joe,

    There is a section in the datasheet that talks about using a GPIO to disable/enable the PCA9306. I would recommend that you do not drive the EN pin to 3.3V but instead tri-state/Hi-Z the GPIO when you want to enable the device and drive the EN low with the GPIO when you want to disable. Driving high to 3.3V directly on the EN pin will prevent the device from properly translating if your side 1 voltage is 1.2V and your side 2 voltage is 3.3V.

    If you follow that set up (disable drive low, enable high-Z) then you can enable/disable 16x PCA9306 devices with the same GPIO assuming your GPIO can sink the current from all 16 pins (should be easy with the 200k pull up resistor).

    -Bobby

  • 0 in reply to BOBBY
    Guru 316780 points

    Figure 9.2 shows driving the VREF2 voltage with a GPIO. (This does not require an open-drain output.)

  • 0 in reply to Clemens Ladisch
    TI__Expert 3115 points

    Hi Bobby,

    Using Figure 9.2 if I tristate the GPIO then I have no voltage for Vref2.

    Or should I not use figure 9.2 but instead connect 3.3V to one side of the 200K resistor and connect the other side of the resistor to Vref2 and connect the EN to the GPIO as you suggest.

    Thanks,

    Regards,

    Joe

  • 0 in reply to Joe DiBartolomeo
    TI__Guru 72981 points

    Hi Joe,

    The 200k resistor on Vref2 will provide the logic high signal to the enable pin if you use the tri-state method.

    The image that Clemen's showcased will work using the push-pull method to 3.3V if you can't or don't prefer to use the tri-state method.

    -Bobby

  • 0 in reply to BOBBY
    TI__Expert 3115 points

    Bobby, Clemen,

    Just to make sure we are all on the same page.  I will tell the customer.

    Use figure 9.2, tied all EN's together, use 3.3V push-pull GPIO, every PCA9306 needs a 200K resistor and current drawn is 168uA (per Clemen's equation).

    Correct?

    Thanks,

    Regards,

    Joe

  • 0 in reply to Joe DiBartolomeo
    TI__Guru 72981 points

    Hi Joe,

    Joe DiBartolomeo said:

    Use figure 9.2, tied all EN's together, use 3.3V push-pull GPIO, every PCA9306 needs a 200K resistor and current drawn is 168uA (per Clemen's equation).

    Correct?

    That is correct. Using you can push pull (3.3V and GND) with that set up as long as you can source the ~168uA current from the push pull driver. 

    -Bobby