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PCA9306: Cascaded I2C translators.

Chaitanya Dasari
Intellectual 280 points
Part Number: PCA9306

Hi E2E

We have connected two PCA9306 in the following manner, will this be an issue?

The datasheet doesn't talk about cascading very clearly. VIH/VIL and VOH/VOL are not defined and we are not very sure there is static voltage offset used on PCA9306.

kindly help us with the above query.

  • 0
    TI__Guru 72771 points

    Hey Chaitanya,

    This kind of set up is acceptable though the 1.8V bus will probably have the hardest time to see an acceptable VoL when the 3V3 master drives low. There will be additional voltage due to the Rdson of the two PCA9306s. This will make the VoL from the master slightly higher.

    You could place the PCA9306 in parallel with each other to try to make this slightly lower since the signal would only have to pass through one PCA9306 instead of two.

    "we are not very sure there is static voltage offset used on PCA9306"

    There is not. This device is not a true buffer but a pass FET based level shifter.

    "VIH/VIL and VOH/VOL"

    ViH/ViL isn't really the parameter I would use to describe how the device interprets the signal as low of high. The device will begin to pass (or block a low if rising from low to high) the signal at around Vref1+0.6V when used in the level shifter set up.

    VoH doesn't really exist in I2C because the high signal is supplied by the pull up resistor so it should be Vcc.Our device does not generate a high, it only passes lows.

    VoL is going to be whatever the driving device's VoL is plus some offset voltage which is dependent on the IoL passing through the device.

    Let me know if you have any follow up questions,

    -Bobby