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SN74LVC1G07: Violation of Input transition rise or fall rate recommendation

Takashi Onawa
Genius 13200 points
Part Number: SN74LVC1G07
Other Parts Discussed in Thread: SN74LVC1G126, SN74LVC1G17

Hi Team,

What is the concern when input slew rate can not meet Input transition rise or fall rate sepc on SN74LVC1G07?
Its output type is Open Drain, so Shoot-through current doesn't matter in SN74LVC1G07 case?

In my customer's system, SN74LVC1G126 is used but input slew rate is very slow like 75us/V.
Output Oscillation doesn't matter on their system because they can change de-glitch time by software but the device might get a damage due to Shoot-through current, so they are looking for any solutions.

I'm wandering if we can suggest to replace to SN74LVC1G17 or SN74LVC1G07, so I want to confirm if  SN74LVC1G07 might get any damages by slow input slew rate.

[FAQ] How does a slow or floating input affect a CMOS device?
e2e.ti.com/.../737694

Regards,

Takashi Onawa

  • 0
    TI__Mastermind 46305 points

    Hey Takashi,

    The SN74LVC1G17 would be the proper device to use here. With the schmitt-trigger inputs there is no cause for concern for oscillations. There will still be an increase in power consumption due to the slow transition, but much less than a normal CMOS input and not enough to harm the device.

  • 0 in reply to Dylan Hubbard
    TI__Genius 13200 points

    Hi Dylan-san,

    Thanks for your quick response on this, and I'm of cause understanding SN74LVC1F17 is the best solution on this.

    The background of my question comes from competitor's reply on this. It seems that one of competitor says that open drain option is also OK to solve this issue. So I need to explain the reason why the option is not recommendable to be correct their understandings. The point of this issue is if the device get any damage by the slow slew rate though, can I have any comments for the point?

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    Guru 318050 points

    Oscillations happen when the voltage at a CMOS input is near the switching threshold and when supply current changes (due to some transistor(s) switching) induce noise on the VCC/GND lines, which changes the switching threshold slightly, which causes the observed input voltage to cross the switching threshold multiple times.

    All this happens at the input. An open-drain device has a different output, but its input still uses complementary transistors. (Furthermore, an open-drain output has a slower rising edge, so it makes this problem more likely when connected to a CMOS input.)