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SN74LV164A: disfunction due to Noise perturbation

François Marconcini
Prodigy 10 points
Part Number: SN74LV164A
Other Parts Discussed in Thread: SN74HCS164

Hello,

We are using the SN74LV164ADR in one of our design, and it seems like a perturbation is creating a strange behavior on the circuit.

In fact, when we have noise (inferior to 1V pp) on ground, the component which normally have a  50Hz clock apply (20ms period) seems to miss a clock rising edge, or to change output at hall of the period, even if the noise is largely inferior to the component input thresholds. This phenomenon is only observable when we connect the mechanical ground of the 2 cards of our circuit, mechanical ground which is perturbated by our converter which generate noise on electrical ground (linked by a 100k resistor to the mechanical ground)

Have you observed such a behavior? Is your component very sensitive to any noise?

  • 0
    TI__Guru* 96591 points

    Hello,

    1V of noise on the ground is a very large amount.

    Generally speaking, CMOS logic devices require a stable supply and clean input signals. There are some devices that add noise margin, such as the SN74HCS164, however this margin is limited and assumes that the noise is on the input signals and not the supply. Sudden, large variations in the supply are very likely to cause errors.