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SN74LV123A: Necessity of Power-up ramp rate

Hiromu Susami
Prodigy 430 points
Part Number: SN74LV123A

Tool/software:

Hi experts,

SN74LV123A Datasheet 7.3 recommended Operating Conditions shows Δt/ΔV Power-up ramp rate(min) = 1 [ms/V]

Q1. Just to confirm, it means we should take moer than 2ms when power up the SN74LV123A right?

Q2. Other genelal purpose Logic IC does't seem to specify Power-up ramp rate. Why SN74LV123A specify this ramp rate?
　In my opinion, I wonder if this is due to the fact that it requires state retation or regulation by an external RC.

Regards,

Hiromu

  • +1
    Guru 299000 points

    1. Yes (this depends on the final supply voltage). Please note that due to all the decoupling capacitors, it is likely that your rate is indeed slower than that.

    2. The '123 has both digital inputs (the triggers) and analog inputs (the capacitors' voltages). A very fast supply ramp rate might result in improper initialization.

  • 0 in reply to Clemens Ladisch
    TI__Prodigy 430 points

    Hi Ladisch,

    Could you tell more detail about Q2? Why does having both a digital and analog input affect the risks of improper initialization?

    Regards,

    Hiromu

  • +1 in reply to Hiromu Susami
    TI__Mastermind 30015 points

    Hi Hiromu,

    If it is ramped too fast, it can cause a false triggers. The output can trigger during power up rather than when you actually want it to.