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Original question:

SN74LV221A: SN74LV221A Shorter pulse than expected on output

SN74LV123A: SN74LV123A vs SN74LV221A CEXT to GND connection

Nicolas Voumard
Prodigy 60 points
Part Number: SN74LV123A
Other Parts Discussed in Thread: SN74LV221A

Hi,

I have a question regarding the connection to GND of the pin CEXT of the monostable SN74LV123A.

In your SN74LV123A datasheet, the CEXT, apparently should NOT be connected to GND, or it is not explicitly sait. (see page 14 and 15 of the datasheet)

In your SN74LV221A, the CEXT pin IS connected to GND.

If I see the datasheet from Nexperia for the 74LV123, the CEXT pin IS connected to GND via pin 8 for noise purpose.

Same on other families of the 74xx123...

Can you please clarify?

Thank you.

  • 0
    Guru 316690 points

    Designing with the SN74LVC1G123 Monostable Multivibrator says:

    5.6 Can I connect the Cext pin to ground?

    It is best to follow the datasheet recommendations. If your monostable multivibrator recommends not connecting Cext to ground, then do not connect it to ground.

    In some monostable multivibrators the Cext pin is internally tied to ground, but in some it is not. If the datasheet is unclear and the information is required, use an ohmmeter to check the resistance between the two pins. If the resistance reads less than 1 Ω, it is safe to connect both to ground.