• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 18 subscribers
  • Views 647 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CD74HC74: Need IBIS model and minimum output transition times.

Scott Asher
Intellectual 500 points
Part Number: CD74HC74
Other Parts Discussed in Thread: CD74HC4049,

Hello, 

I need an IBIS model for the CD74HC74M. I could not find one on the website. I need a model that accurately models the output transition times tTLH and tTHL, especially the minimum times. I tried using a model for another part in the same family, the CD74HC4049 since its datasheet showed the same output transition times. But simulations using this model did not appear to be accurate respresentation of the datasheet specs. For example, the datasheet specs tTLH and tTHL for CD74HC4049 (and for CD74HC74) are 15ns max @25C, 19ns max @ -40 to 84C, and 22ns max @ -55 to 125C for 50pF load. But when I simulate the Slow-weak case in Hyperlynx with CD74HC4049 model driving a 50pF capacitor, I only get Trise = 5.844ns and Tfall = 3.920ns which is much less than the datasheet specs. This was for 10 to 90% as specified in the datasheet. 

Can you provide an IBIS model that accurately models the minimum tTLH and tTHL output times of the CD74HC74M? As long as it has the same characteristics as the CD74HC74M is all that matters. 

Also, please provide what the minimum tTLH and tTHL times of the CD74HC74M should be for a given load so I can confirm by simulation the accuracy of the model that you provide. The datasheet only specifies the maximum tTLH and tTHL times.

Thanks,

Scott

  • 0
    TI__Guru* 96591 points
    Hi Scott,
    Using a similar device would have been my first recommendation and still is the best option.

    I can ask our modelling team to look at the HC4049 model to see if there's an issue with it, however it's unlikely that we're going to be able to get a new model for the CD74HC74 since this device was acquired from Harris Semiconductor and all the files required to generate a simulation/IBIS model are likely not available.
  • 0 in reply to Emrys Maier
    Intellectual 500 points

    Hi Emrys, thanks for the reply!

    Until the modeling team responds, in the meantime is there any other devices that have similar output specs like the CD74HC74 that you have a model I could try?

    Also, please provide what the minimum tTLH and tTHL times of the CD74HC74M should be for a given load so I can confirm by simulation the accuracy of the model that you provide. The datasheet only specifies the maximum tTLH and tTHL times.

    Thanks again!

    Scott

  • 0 in reply to Scott Asher
    TI__Guru* 96591 points
    Hey Scott,
    We don't have minimum propagation delays for device. I will have to look at it in the lab to get a typical value for you. I should get samples early next week.
  • 0 in reply to Emrys Maier
    TI__Guru* 96591 points

    Hey Scott,

    I was able to pull some data for you -- here's a few typical waveforms for the CD74HC74.

    All tests were performed at 25C on a 50pF load

    Figure 1 - 6V output

    Figure 2 - 6V output, zoomed rising edge

    Figure 3 - 5V output

    Figure 5 - 5V output, zoomed rising edge

    Figure 6 - 3.3V output

    Figure 7 - 3.3V output, zoomed rising edge

    Figure 8 - 2V output

    Figure 9 - 2V output, zoomed rising edge

    Figure 10 - 5V operation, rising edge delay (clock to output), 12.08ns

    Figure 11 - 5V operation, falling edge delay (clock to output), 10.56ns