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SN74HCS74-Q1: Q status when power off

song.lin
Prodigy 190 points
Part Number: SN74HCS74-Q1

Hi Expert

What's the output status of Q when the power on VCC loses? The initial output status is high. Will it be float(tri-state) or pulled to low?

  • 0
    Guru 277220 points

    In theory, the output has high impedance. But there are diode clamps from all I/O pins to VCC, so the voltage cannot rise to above about 0.6 V, and if you try to apply a higher voltage, a current will flow into the supply and might (partially) power up any device connected to it. And if the absolute maximum rating of 20 mA is exceeded, the device might get damaged.