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PCA9306: PCA9306 - what about INT signal?

Yigal BenZeev
Prodigy 30 points
Part Number: PCA9306
Other Parts Discussed in Thread: PCF8574, , TXU0101, SN74AXC1T45

The PCA9306 is a good solution to my needs, but sometimes there is a need to transfer the INT signal, from example from a device like pcf8574.

Is there a similar product that can interface 3 signals instead of the 2 (SCL, SDA)?

Or is there any other idea how to create interrupt at the master CPU when an event occurs at the I2C device?

  • 0
    Guru 257720 points

    The /INT signal is unidirectional, so you could add a one-channel translator like the SN74AXC1T45/TXU0101, or just omit the translator if the microcontroller has a lower voltage.

    If you do not need very high speeds, you can connect EN directly to the lower voltage and use VREF1/VREF2 as a third channel.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    It is true that /INT is unidirectional, yet since it has to be wired together with the GND, SCL, SDA cable, it could have been nice to have it on same chip. This will force me to add a 2nd chip to the PCB. Not a showstopper though.

    I forgot to mention I need 3.3V on the CPU side, and 5V on the client side, so the SN74AXC1T45 is not a good fit (max 3.6V), yet the TXU0101 seems to be a good fit. 

    so as for now it seems that the project will include pcf8574 with:

    - 5V PCF8574  VCC device on the client side (there are few such clients on the I2C bus)

    - 2 meter cable

    - PCA9306 & TXU0101 with 5V on the outside, and 3.3V on the inside for the CPU (ESP32 in this case).

    Does it seems reasonable? Do you have a better idea/suggestion?

  • 0 in reply to Yigal BenZeev
    Guru 257720 points

    /INT is an open-drain signal; you can just use a pull-up to 3.3 V without a translator.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    Are you suggesting that the PCF8574  will operate on 5V, yet the /INT output will be tied to 3.3V pull up resistor? 10K ohm like the SCL, SDA?

    The resistor will reside on the ESP32 master side, not close to the PCF8574  - I assume this is not an issue.

    Will it work on I2C 2 meter long cable from the client to the master?

    I was assuming that 5V will give a better immune to noise.

  • +1 in reply to Yigal BenZeev
    Guru 257720 points

    Yes, an open-drain output never drives high, so you can pull it up to any voltage not above VCC.

    What matters most for noise immunity is the strength of the pull-up.