SN74LVC74A-EP: D-flipflop is triggering at rising and falling edges.

Abhay Tyagi

Part Number: SN74LVC74A-EP
Other Parts Discussed in Thread: SN74HCS74

Dear team,

We are working on D-flipflop, but it gets triggered on both rising and falling edges. (From datasheet it is observed that CLK should trigger on rising edge only).

We are providing 2.85V at VCC, PRE, 1D and 2.9V at 1CLK with 0.2Hz frequency.

In this image Yellow signal is 1CLK and Green signal is Output (1Q).

Regards

Abhay Tyagi

over 3 years ago

0 Abhay Tyagi over 3 years ago

Prodigy 15 points

Please find the schematic for above observation.

0 Sebastian Muriel over 3 years ago in reply to Abhay Tyagi

TI__Mastermind 21080 points

Hi Abhay,

The input signal to the clock is too slow. The maximum input transition rate in the datasheet is 10 ns/V and cannot be violated for functional operation of the device. Please see this FAQ How does a slow or floating input affect a CMOS device? for further details.

Regards,

Sebastian

0 Abhay Tyagi over 3 years ago in reply to Sebastian Muriel

Prodigy 15 points

Hi Sebastian,

1.Could you please suggest any similar part which we can use in slow rising inputs? Can we use SN74HCS74 for slow rise inputs.

2. Kindly share the simulation model for SN74LVC74A-EP. Can we identify such issue in simulations

3. Datasheet page-1 state that clock depend on voltage level only not on rise time. Does that mean other input like D, CLR, PRE requires fast rise time, not clock.

regards

Abhay

0 Sebastian Muriel over 3 years ago in reply to Abhay Tyagi

TI__Mastermind 21080 points

Hi,

1) The SN74HCS74 would be a drop in replacement that would fix the issue.

2) Unfortunately we currently do not have any simulation models for D Flip Flops

3) The CLK pin is still a CMOS input and cannot violate the input transition rate spec for proper operation.

Also I see you have an RC filter on the input, if this isn't necessary removing the capacitor might fix your slow input.

Regards,

Sebastian

Logic

Logic forum

SN74LVC74A-EP: D-flipflop is triggering at rising and falling edges.