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SN74LVC244A: NO power on SN74LVC244A, and then output waveform in different conditions

Thomas Chang15933
Expert 4770 points
Part Number: SN74LVC244A

Dear Team:

  Our customer used SN74LVC244APWR in server, and some condition is without power over the chip, so they want t know our output behavior as below setting.

 1. If VCC pin (P3v3) no power, pin (A1 ~ A8) have PWM signal input , what is output waveform?

2. If VCC pin (P3v3) no power ,Output pinpin (Y1 ~ Y8)  already have weak pull high 5V , How much the output voltage will be  drooped to  low ? Waht is output waveform? 　

  • 0
    TI__Guru* 96947 points
    Hello Thomas,
    How do you define "no power"? Is the Vcc pin forced to 0V when no power is applied, or is the Vcc pin at some lower voltage than the normal 3.3V? Both cases are fairly common, which is why I ask.

    The Vcc pin _should_ be forced to 0V when the power is off, which means the device enters Ioff protection mode, and all I/O pins go into a high impedance mode (maximum leakage specified as Ioff in the datasheet).

    If this is the case, and there are 5V pull-ups on the outputs, then the outputs will be at 5V (after however long it takes the weak pull-ups to drive them to 5V).