SN74AHC1G08: Input transition rise or fall rate Δt/Δv define in datasheet

CHIANG CCH

Part Number: SN74AHC1G08

I am confused about the specification for "Input transition rise or fall rate Δt/Δv". According to the specification, the maximum value is 100 ns/V (Vcc=3.3V). Does this mean that the rise time or fall time of the input signal must be less than 100ns/ (2.1V-0.9V) = 83.3ns

In my past experience, I have been concerned about the rise or fall time being too fast, which can cause incorrect identification or overshoot/undershoot in the waveform due to higher energy levels. So why does TI define the rise or fall time to be less than 83.3 ns in this specification? What are the consequences if this requirement is not met?

Thanks

Regards

Albert

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 281530 points

Slow edges can lead to increased power consumptions and damage; see [FAQ] How does a slow or floating input affect a CMOS device?

0 CHIANG CCH over 1 year ago

Prodigy 30 points

Thanks for your reply, if the INPUT is pulled HIGH to the same power rail as the LOGIC IC VCC, because the rise and fall times of the VCC power rail during power on or power off are in the range of milliseconds level, making it difficult to meet the requirement of nS for input transition rise/fall rate. Therefore, the input transition rise/fall rate fails every time the logic IC power is turned on or off. However, once power is on, the rise/fall time of the input is within spec. Do I need to be concerned about the logic IC failing on input transition rise/fall rate during power on and power off?

0 Clemens Ladisch over 1 year ago in reply to CHIANG CCH

Guru 281530 points

The switching thresholds scale with V_CC, so you do not need to care about power up/down. (But below the specified minimum supply voltage of 2 V, correct operation is not guaranteed.)

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SN74AHC1G08: Input transition rise or fall rate Δt/Δv define in datasheet