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CD74HCT4052: #E is given a high level before VCC is ready

Ann_Lien
Genius 11680 points
Part Number: CD74HCT4052
Other Parts Discussed in Thread: CD74HC4052

Hello expert,

My customer is wondering if it is okay that #E is given a high level before VCC is ready. They used CD74HCT4052 in audio application and they have issue with no sound board. After checked, they found out #E is given a high level before VCC. They are wondering if they will have problem on this sequence. Thanks a lot!

Best regards,

Ann Lien

  • 0
    TI__Genius 10974 points

    Hi Ann,

    By biasing the the #E pin prior to VCC you risk back powering the mux as well as potentially any downstream devices in the signal path. So basically, things might be turning on when they are not supposed to be on yet, which may or may not affect the circuit depending on what is being turned on at what time.

    Thanks!

    Bryan

  • 0 in reply to Bryan Marshall
    TI__Genius 11680 points

    Hello Bryan,

    Thanks for reply. May I know which channel will turn on which channel won't? Customer is under debugging and hope we can provide some clues to them. Thanks a lot!

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    Guru 267180 points

    A current flows from the input into VCC, which means that the CD74HC4052 device (and any other devices connected to this supply) might be powered on, or partially powered on so that they do not work directly.

  • 0 in reply to Ann_Lien
    TI__Genius 10974 points

    Hi Ann,

    It is difficult to say what will turn on, there is just a path created that allows other devices to possibly see that "high level" voltage. I would advise your customer to probe the downstream devices and possibly VCC node to see if it is seeing a voltage it is not supposed to when everything is powered off with just #E pin input voltage present.

    Thanks!
    Bryan