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CD74AC109: Master Slave JK Flip-flop configuration

Vinnie Gupta
Prodigy 20 points
Part Number: CD74AC109
Other Parts Discussed in Thread: CD4027B, , SN74HCS74, SN74AUP1G80

Dear TI team,

I want to use a master slave JK Flip flop to toggle the output when Clk is generated. A tactile switch will be connected on clk signal to operate it as on/off switch at +ve edge trigger. Output acts as ON when the switch is pressed once, next time the output turns OFF when switch is again pressed. To avoid "racing", I wish to use a master slave JK FF and "CD4027B" is of a kind but the minimum supply voltage in my design is 2.4V. Hence, can you suggest any alternate part?

Moreover, I want to know if I can configure "CD74AC109" as master slave FF as it is a dual FF and I am using only one of it. Need your guidance on how shall I configure it to operate as master slave JK FF.

Regards,

Vinnie

  • +1
    Guru 317280 points

    For handling a mechanical switch, you do not need a master-slave flip-flop. Just use a D-type flip-flop (e.g., SN74AUP1G80 or SN74HCS74) and feed back the inverted output to the D input.

    (Don't forget to debounce the switch signal.)

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Dear Clemens,

    Thank you for the suggestion.

    Based on supply range, SN74HCS74 is suitable. In the datasheet, below circuit is explained in the application which has RC network for debounce of the switch. I hope this is sufficient. Is there any specific value that should be used for C1 and C3?

    Moreover, I believe I can use only one flip-flop and connect remaining pins to Gnd (after confirming each pin termination from datasheet).

  • +1 in reply to Vinnie Gupta
    TI__Mastermind 18270 points

    Hi Vinnie,

    R3 and C3 should have a larger time constant than your debounce circuit. This will prevent any false triggers at startup. I would aim for the switch to bounce for less than 20ms as a starting point. 

    Regards,

    Sebastian