SN74LVC2G241: Output of Buffer turns on before meeting minimum input high voltage

Peter Davis1

Part Number: SN74LVC2G241
Other Parts Discussed in Thread: TLV7031, TLV803E, TLV4041

Hello we are using the SN74LVCG241 in a power-up sequence circuit that has critical timing requirements. The issue we see is the output of the buffer goes high once the input of the buffer = 1.4V. However, according to the datasheet the minimum high-level input voltage should be 2V with a VCC of 3V to 3.6V (We are using 3.3V)

Does the Buffer input enter an unknown state between 0.8V and 2V? Will this input high threshold voltage vary by device? See the plot below:

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 212110 points

The datasheet guarantees that the output is high when the input is at least 2 V, and that the output is low when the input is at most 0.8 V. The actual switching threshold is likely to be near V_CC/2, but there are no guarantees for any voltage between V_IL and V_IH.

(Furthermore, signal edges slower than the specified Δt/Δv limit will increase power consumption and can lead to oscillations and damage; see [FAQ] How does a slow or floating input affect a CMOS device?)

If you want a more precise switching threshold, use a comparator like the TLV7031/2 or TLV4041. There are also voltage supervisor ICs like the TLV803E.

0 Peter Davis1 over 1 year ago

Intellectual 360 points

Hi Thanks for the quick reply, that makes sense. Is this also true for the enable pin? in that the threshold is typically near VCC/2, and there is no guarantee for the turn on voltage? Could this also cause issues if we don't have a fast enough dt/dv on the OE pin?

+1 Clemens Ladisch over 1 year ago in reply to Peter Davis1

Guru 212110 points

These specifications apply to all digital inputs.

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SN74LVC2G241: Output of Buffer turns on before meeting minimum input high voltage