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TXS0108E: Vcc isolation and OE VCCA reference

Josh Wilson
Prodigy 120 points

Part Number: TXS0108E
Other Parts Discussed in Thread: TXB0108,

I have two issues that I am trying to resolve before proceeding with using this part. We were originally looking at using a TXB0108 due to the datasheet stating that there is a Vcc isolation feature which we need.

 From the TXB0108 datasheet: VCC Isolation Feature – If Either VCC Input Is at GND, All Outputs Are in the High-Impedance State

I am wondering if the TXS0108 also has this VCC isolation feature, i.e. are the output high impedance when the device is powered off?


Second question is related to the OE pin, we are connecting a 1.5V FPGA I/O to 1.8V Microprocessor I/O with this part so our VCCA=1.5V and VCCB=1.8V. The issue is we would like to drive the OE pin from the microprocessor side which is 1.8V logic. Can the OE pin be driven from 1.8V I/O even though it is referenced to VCCA which in this case is 1.8V.

 

 

  • 0
    TI__Guru 63830 points
    Hi Josh,

    The TXS0108e doesnt indicate that the device supports Ioff partial power down. To be sure, you can apply 0V on Vcca ( or Vccb) and see if the powered up side ports are pulled to their respective Vcc level. During Hi-Z, the internal pullup resistors must be disconnected and the signals on the ports would not be back driving the Vccx supply.
    From the electrical spec, at Vccx = 0V, the Icc current is within 2uA.

    The OE is overvoltage tolerant and hence can tolerate 1.8V with the Vcca at 1.5V.