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SN74ALVC244: Damage to the output pin if the device has no power

Danilo A.
Mastermind 24705 points
Part Number: SN74ALVC244

Hi Team,

We've received an inquiry from a customer about two SN74ALVC244 with same supply voltage level (3.3V) but different power source. The output of the first buffer (A) goes to another buffer (B) and there is a 1k ohm pullup resistor (tied to VCC of buffer B) between the two buffers. He would like to confirm if the output of buffer A will be damaged when it's supply is off considering there is a 1k ohm pullup resistor connected to the power source of buffer B.

According to the customer

"I see in the absolute max rating the note 2 and 3 that its looks like as long as the current is below 50mA the output voltage can get up to 4.6V without being damaged even if VCC is 0V. is this correct?"

Regards,

Danilo

  • 0
    TI__Guru* 96591 points

    Hi Danilo,

    There is a diode between the output and the supply, so exceeding the supply value + ~0.7V will cause the diode to forward bias and current will flow from the output to the supply pin. This is often referred to as "back powering" as it can result in the rail being energized enough to power circuits.

    As long as the current through the diode is limited, there will be no damage to the device. I would recommend to keep it below 50mA.

  • 0 in reply to Emrys Maier
    TI__Mastermind 24705 points

    Hi Emrys,

    Thank you for the clarification.

    Regards,

    Danilo