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PCA9306: Several questions about the PCA9306

Lacey Lin
Intellectual 2900 points

Part Number: PCA9306

Hi team,

My customer wants to use the PCA9306 in their design and hope to know the answer for the questions.

1. What's the value of the Ron when the Io is 0.5mA,1mA and 1.5mA. Is it fixed or changed by the setting?

2. What's the relationship of the SCLK1 and SCLK2 or SDA1 and SDA2? I have saw some posts say that when the voltage of the SCLK1 is high and the voltage of the SCLK2 is decided by the VDPU.

3. Customer wants to connect 4 devices in the I2C bus. I have found the description for the limitation in the datasheet.

So it means the sum of the load of SDA1 and SDA2 need to less than 400pF. Is it correct?

4. Can we connect the EN pin and REF2 separately?

Lacey

Thanks a lot!

  • 0
    TI__Guru* 78461 points

    Hey Lacey,

    "1. What's the value of the Ron when the Io is 0.5mA,1mA and 1.5mA. Is it fixed or changed by the setting?"

    -Ron does change with the current draw but from my understanding this change will be small. I believe the voltage on the EN pin has a larger effect as seen by figure 1 and 2 in the datasheet.

    I've done some testing in the lab before on the Ron parameter though this is a bit different from your case as it was in respect to temperature; the IoL in the tests were around 2mA and 1mA which resulted in about ~5 ohms and ~3 ohms respectively at room temperature.

    See below for more details:

    "2. What's the relationship of the SCLK1 and SCLK2 or SDA1 and SDA2? I have saw some posts say that when the voltage of the SCLK1 is high and the voltage of the SCLK2 is decided by the VDPU."

    SCLK1 will be the pull up voltage it is tied to and SCLK2 will also be the pull up voltage it is tied to when the signal is high. This provides the "voltage separation" for the voltage translation. SDA1 and SDA2 are the same way. When one signal is pulled low, the opposite side will follow it after a small delay (expect the delay to be in the range of nano seconds and dependent on multiple parameters).

    "3. Customer wants to connect 4 devices in the I2C bus. I have found the description for the limitation in the datasheet.
    --datasheet picture--
    So it means the sum of the load of SDA1 and SDA2 need to less than 400pF. Is it correct?"

    Because this device supports up to 400kHz, the I2C standard states the maximum capacitance allowed at this speed is 400pF. This device does not buffer capacitance so you are correct. SDA1/SDA2 and SCL1/SCL2 must not exceed 400pF (when enabled).

    "4. Can we connect the EN pin and REF2 separately?"

    -Can you draw a diagram of what you mean? This device can be configured outside what the datasheet discusses but it is a little but trickier and configured wrong could damage the device. I assume you want to tie the EN pin to a GPIO to get more control of the device.

    Thanks,

    -Bobby