TCA9406: OE PIN configuration

Hey AGXIN,

TCA9406 does not have to be pulled up to VCCA but it should already be referenced to VccA internally through a weak pull up resistor. By doing this externally you will have a better pull up than what is provided.

"Is this because of the Tolerance level of the pin is similar to VCCA ?"

-The tolerance of the OE pin allows for 5.5V.

"Why is this recommendation made?"

To ensure this reference voltage is high and the pin does not see noise (EMI coupling to the pin and pulling it low) or crosstalk which could pull it low. A stronger pull up will ensure it stays on when it is meant to stay on.

Thanks,

-Bobby

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EDIT: It was brought to my attention that you may have been referring to this table.

The device is comparing the voltage of the OE to a ratio of VccA. Where if the OE pin is above 0.65xVccA, the pin is said to be high and the device is enabled. When OE pin falls below 0.35xVccA the device will be disabled and lows will not propagate from A to B or B to A. Thus it is recommended if you intend to enable this device, you should keep OE pin higher than 0.65xVccA which pulling up to the VccA will ensure.

Hey Adrian,

If VccA=VccB then I think this set up would be okay. If VccB is larger than VccA then we do have a case where there are two voltages between a resistor where current will go from VccB to VccA and may cause issues, in this case I would not connect VccB to VccA. Lastly the case where VccA is larger than VccB should not be allowed (device recommends VccA=<VccB) and VccB should not be tied to the OE.

Thanks,
-Bobby