What is the minimum VIH value for the SN74HC74 flip-flop when supplied with 3.3V?

JG88

Other Parts Discussed in Thread: SN74HC74

I'm driving the 1CLK input of a SN74HC74 flip-flop, which is powered by Vcc = 3.3V, with a logic signal whose high value is 2.57 volts. Is this voltage high enough to trigger the flip-flop? The datasheet only specifies VIH for VCC = 2V, 4.5V, and 6V. The states of the other input pins are:

n1CLR: 3.3V
1D: 3.3V
n1PRE: 3.3V
GND: 0V
VCC: 3.3V
n2CLR: floating
2D: floating
2CLK: floating
n2PRE: floating

over 13 years ago

0 Chris Cockrill over 13 years ago

TI__Mastermind 46480 points

Vil = 0.3 x Vcc Vih = 0.7 x Vcc

For 3.3V Vcc Vih would be 2.31V. You are good.

0 Chris Cockrill over 13 years ago in reply to Chris Cockrill

TI__Mastermind 46480 points

You should also not float 2clr and 2pre.

0 JG88 over 13 years ago in reply to Chris Cockrill

Prodigy 120 points

Then is there any other reason that the flip-flop state would not change (1Q high, n1Q low) despite pulsing 1CLK? I know it's bad practice to leave those other pins floating, but could they have to do with the problem of FF1 not changing states?

0 Chris Cockrill over 13 years ago in reply to JG88

TI__Mastermind 46480 points

This is not a JK flipflop so the output will not tooggle when the clock toggles unless the data toggles. In other words on the rising edge of the clock the data will pass to the output

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What is the minimum VIH value for the SN74HC74 flip-flop when supplied with 3.3V?