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Product selection help

M-Dizzle
Prodigy 435 points
Other Parts Discussed in Thread: SN74F112, SN74F109

Hi guys,

 

Below is a new customer inquiry:

I want to split down frequencies in range from 2MHz to 150MHz / 170MHz (if possible ... to 450MHz). It does not matter to me whether this is a counter or a JK flip-flop ... or another type of split. It should be possible to bring up the input frequency in the range of a few MHz. Ok is also a firm split factor of for example 4:1 or

x: 1.

 

 Do you have such a device? If possible the price should be 2 or 3Euro max ... 70Cent would be even better. What I found is the JK-FF SN74F109 or SN74F112. However, according to the datasheet it can do only 114MHz. Is this correct or can I use this JK-FF also to 150MHz or 170MHz?

 

Here, the data from Farnel:

FAIRCHILD SEMICONDUCTOR
SN74F109D, respectively SN74LVC112AD

IC, LOGIC GATE, FLIP-FLOP

Flip-Flop type: JK; time, Transmission delay:6ns; Frequency:150MHz; Output Current: 24mA; Trigger type: Positive Edge; Supply voltage range: 2V to 6V; Logic IC package: SOIC:

...but according to the datasheet anyway only 114MHz!!!

 Thankful for help!

Kind regards M-Dizzle

 

  • 0
    TI__Mastermind 46480 points

    What is your power rail? 

    We do have some little logic devices that can run up to 200Mhz at 5V. http://focus.ti.com/lit/ds/symlink/sn74lvc1g74.pdf

    To divide by 4 It would require more than 1 part but should still meet your budget.

     

     

  • 0 in reply to Chris Cockrill
    Prodigy 40 points

    Thanks for your answer.

    (The power rail is not the main issue) I already saw this part ....it's a D-FlipFlp. I don't think that I can build a frequency devider with a D-FF. A fast devider only can be build with JK-FF, can't it? If you wire the output of a D-FF back to data-input of the D-FF then you have to wait a "long" time until the data is stored at the data-input. I tried it already in other applications.

    If it is possible to build a fast devider with a D-FF, please send me the schematic to "t.dorn@thomasdorn.de". Thanks a lot in advance for your effort.

    One question of me was if the SN74F109D or/and the SN74LVC112AD are able to process 170MHz  to make a devider. In the datasheet you can read 114MHz as the maximum frequncy but at the distributer you can read 150MHz, ....which value is the right one.

    By the way, ...if the levels of the JK-FF do not reach the supply voltage it doesn't matter, ...I can use a driver afterwards.

    Regards, Thomas

  • 0 in reply to Thomas Dorn
    TI__Mastermind 46480 points

     

    The F109 is rated for 100Mhz while the LVC112 is rated for 150Mhz at 3.3V.  The LVC1G74 is rated for 200Mhz and can be used at 5V.  To use the D-Flip Flop as a divider you would tie the Qbar output to the D pin. The output would be on Q and input on the clock pin.

     

  • 0 in reply to Chris Cockrill
    Prodigy 40 points

    I already tried to do it like this for projects before ....it doesn't work for fast applications because...

    Start values:

    clk="0", D="0", Q="0", Q_not="1"  --> We can use Q_not for data input to get the "1" for toggling  ...that's  o.k. so far, ....BUT

    if  you rise the clk, then the Q_not toggles "immedeately" to "0" !!!!! But the D input has to be remained to "1" for a specific time!!! Otherwise the "1" wiill not be carried by the FF!! ...and so the output doesn't toggle!

     

    Did you already test "your" theoretical "devider"? .... and at this frequency...? I know, in some books this schematic works theoreticaly, but to get this running, you have to place a "big" time delay between Q_not and D. And then you can't make a devider for this high frequency.

     

    Maybe you know somthing new about this for me? But thanks for looking for the LVC112. I think I will use this one. It should work up to 160MHz or even 170MHz ...but this I will test.

    Best regards, Thomas