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SN74HC164: No shift between Output A and B

Manu Chang
Intellectual 1980 points
Part Number: SN74HC164
Other Parts Discussed in Thread: SN74HCS164

Hi，

my customer is having some problem with using SN74HC164, schematic as in first figure. When customers changed the input DATA and CLK to Open Drain output, they found that there are no shift on the output A and B of SN74HC164. 

As showed in the second figure, Red is the DATA and Yellow is the CLK.  Blue is output A and Green is output B. As you can see there is no shift between A and B, other outputs are quite normal.

What root cause may lead to this problem？

Red: DATA;  Yellow : CLK ; Blue : output A ; Green : output B

Manu

  • 0
    Guru 316690 points

    The input signal edges are too slow; they violate the specified Δt/Δv limit. This leads to oscillations, which are interpreted as multiple clock pulses.

    Such slow edges can be handled by a device with Schmitt-trigger inputs, i.e., the SN74HCS164.