SN74LVC1G123: False Output at start up

Guru 15590 points

Replies: 2

Views: 44

Part Number: SN74LVC1G123

Dear Specialists,

My customer is evaluating SN74LVC123 and encountering a problem.

I would be grateful if you could advise.


In SN74LVC1G123DCUR, one pulse signal of about 80ms is output from output terminal Q at 0.93V 

on the way from Vcc = 0V to 5V.

 (In the system, the circuit in the subsequent stage will operate due to the influence of the output signal.)

 (1)Could you please let us know the cause of the phenomenon.

 (2)We'd like to know how the risig and falling edge of the A, B and CLR determined.

Could you please see the waveform and schematic.

Question about SN74LVC1G123DCUR.xlsx

According to the Function Table, a pulse may be output when the IC_B or CLR transitions from L to H.

However, 0.93V is out of the operating rating.

We are looking forward to waiting your advice.


I appreciate your great help in advance.

Best regards,


2 Replies

  • Hi Shinichi,

    Thanks for the details you provided. This device should have a clear circuit to keep the output from powering up High. Can you test without the output load? Also can you add a scope channel to the Rext/Cext pin?

    What is happening to the A input? I don't see what its all connected, but what I can see is an RC circuit connected between it and Vcc so I wouldn't expect it to track the supply like it does.

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  • In reply to Dylan Hubbard:

    Hi Dylan,

    Thank you for your reply.

    I'll confirm with the customer about your comment.

    When I get information, I'll feedback to you.

    I appreciate your great help and cooperation.

    Best regards,