Electronic – High level present in a pin of a non-powered IC can damage it

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I'm using a TXS0108E to convert from 5V to 3.3V and vice versa. The schematic is below:

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In the datasheet, in section 6, I read the following:

Voltage applied to any output in the high-impedance or power-off state, VO:

A port : 

     MIN: –0.5V
     MAX: 4.6V

B port: 

     MIN: –0.5V
     MAX: 6.5V

Voltage applied to any output in the high or low state, VO

A port:

    MIN: –0.5 
    MAX: VCCA + 0.5 V

B port:

    MIN: –0.5 
    MAX: VCCB + 0.5 V

Some of pins in B port are energized when the IC is not powered at all. So I was wondering, would this be a problem ? Normally it is a problem to ICs, would this IC be a exception ?

Best Answer

Absolute Maximum Ratings indicate limit that will not cause any damage to the device, but don't mean that it will behave properly at those limits. Most devices have clamp diodes for ESD that can allow a voltage at any pin to unintentionally energize the device. The datasheet says

To ensure the Hi-Z state during power-up or powerdown periods, tie OE to GND through a pull-down resistor. The minimum value of the resistor is determined by the current-sourcing capability of the driver.

so I'd guess that so long as this is observed, the chip should behave as intended, i.e. do nothing with an input while not powered.

You do need to take care that there are no loads on the Vcc lines that can draw current back through the protection diodes.

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