SN74AVC4T774: I/Os impedance when device is powered down

Alex Kucherov

Part Number: SN74AVC4T774

Hello,

The datasheet for the SN74AVC4T774RSV states that the device is specified for partial power-down and the Ioff circuitry disables the outputs when the device is powered down.

Does this mean that I can safely drive the inputs of the SN74AVC4T774RSV when it is fully powered down (both VCCA and VCCB are at GND) ?

Do I need to worry about current flowing through the internal protection diodes to VCCA or VCCB?

Thanks,

Alex

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 243820 points

This device does not have protection diodes to V_CC. See [FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?

0 Alex Kucherov over 3 years ago in reply to Clemens Ladisch

Prodigy 220 points

OK, so does this mean that I can safely drive the device inputs when it is fully powered down? Are the inputs high impedance in this case?

0 Clemens Ladisch over 3 years ago in reply to Alex Kucherov

Guru 243820 points

Yes.

0 Alex Kucherov over 3 years ago in reply to Clemens Ladisch

Prodigy 220 points

OK, thank you.

So, just to make sure I understand the device operation correctly, are the following statements correct?

1. If an I/O is configured as input it will always be high impedance whether the device is fully, partially or not powered at all.

2. If an I/O is configured as output it will be high impedance if the device is partially powered or not powered at all (irregardless of the OE pin).

3. If the device is fully powered, only then does the state of the output is determined by the OE pin.

0 Clemens Ladisch over 3 years ago in reply to Alex Kucherov

Guru 243820 points

Yes.

Logic

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SN74AVC4T774: I/Os impedance when device is powered down