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SN74LS123: Glitch upon power-up

Jejomar Ildefonso
Expert 8770 points
Part Number: SN74LS123
Other Parts Discussed in Thread: SN74LVC1G123

Hi Team,

Is there a proper power-up condition for SN74LS123. Our customer is currently having issues with SN74LS123 wherein the device generates pulses in both of the outputs upon connecting it to power. Can you help us?

We're thinking the issue is caused by a power-up glitch, similar to the situation discussed on this thread for SN74LVC1G123: https://e2e.ti.com/support/logic-group/logic/f/logic-forum/955647/sn74lvc1g123-glitch-free-power-up-reset-on-outputs---

Thanks in advance!


Kind Regards,

Jejomar

  • +1
    TI__Guru* 96681 points

    Hi Jejomar,

    The SN74LS123 is a biplar logic design -- I would recommend to have a stable 5V supply for quite some time (at least 5*R*C) before expecting the device to operate normally. It was not designed for modern systems with sudden power changes.

    Have they considered using a more modern MMV such as the SN74LVC1G123? As you pointed out, it includes pulse-suppression circuitry for power-up and also will operate at 5V.