SN74AUP1G57: SN74AUP1G57

Chundra Ramful1

Prodigy 250 points

Part Number: SN74AUP1G57
Other Parts Discussed in Thread: SN74AUP1G97, SN74AUP1G98, , SN74AUP1G58

Hi,

I am referring to the following “Low Power Configurable Multiple-Function” gates:

a) SN74AUP1G97

b) SN74AUP1G98

c) SN74AUP1G57

d) SN74AUP1G58

The datasheets do not provide any minimum value for the input voltage slew rate. They basically state that the Schmitt-trigger inputs will allow for slow signals at the input. I am designing circuitry for an energy harvesting application where some of the signals may take anywhere from 5 minutes to 30 minutes to ramp from ground to the desired voltage at which switching should occur. Can the Schmitt-trigger inputs in the above part numbers accommodate the inputs I am talking about?

Thank you!

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 278600 points

This is OK. There is no limit for the transition time.

Please note that an input voltage not near the rails will cause cross currents in the input transistors, which increases the supply current. This is specified as ΔI_CC. If you want to reduce that, you have to use a comparator instead.

0 Chundra Ramful1 over 4 years ago in reply to Clemens Ladisch

Prodigy 250 points

Hi Clemens,

Could you please provide more details on "cross currents"? Perhaps a schematic of the internal structure may also help me understand what you trying to say.

Thank you,

Chundra

0 Emrys Maier over 4 years ago in reply to Chundra Ramful1

TI__Guru* 96842 points

Hi Chundra,

Schmitt-trigger devices use a feedback network to adjust the input threshold. This network draws more current when the input is closer to the threshold and less when it is further away. Since you have selected a 'low power' logic device, I would assume that you are concerned with power consumption -- the device will draw a great deal more power while the input is slowly ramping (up or down) than it will while the input is held at either rail.

I can't share the exact structure of our inputs, but I can give you a basic Schmitt-trigger input structure from a quick search:

From: https://www.researchgate.net/figure/Low-voltage-CMOS-Schmitt-trigger_fig2_319857835

There's an FAQ that discusses a similar occurrence in standard CMOS inputs here:

[FAQ] How does a slow or floating input affect a CMOS device?

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SN74AUP1G57: SN74AUP1G57