[SN74AUC] Lighter Load Characterization

Benjamin Mak

Hi Team,

I am planning to use the SN74AUC family at 1.8V.

I understand that the parts are spec'd with a 15pF load. Is there any sort of characterization for a smaller load?

I am looking at a solution for a CMOS parts that would work at 1066Mbps per pin. The switching frequencies are not given in the datasheets; will this family be sufficient for that speed?

Thanks,

Ben

over 11 years ago

0 Avi Chami1 over 11 years ago

Mastermind 7395 points

Hi,

I don't think so.

The input slew rate is limited to 20 ns/V, I guess that a 1Gbps signal will have a much faster slew rate.

0 Benjamin Mak over 11 years ago in reply to Avi Chami1

TI__Intellectual 2190 points

Hi Albert,

Thank you for your response!

How would I go about calculating the necessary slew rate for this particular application?

I know that the voltage levels are 1.8V. Would the slew rate have to be larger than... 1 / ((1066 * 10 ^ 6) * 1.8)? Or do I need to factor in a 2 somewhere?

Thanks,

Ben

0 Avi Chami1 over 11 years ago in reply to Benjamin Mak

Mastermind 7395 points

Benjamin, if your slew rate was calculated in the way you wrote, the signal would have been triangular, not square.

It is difficult to say what slew rate you will have, for lower speed signals the rise time is usually in the order of 1/10 of the period. For faster signals it is difficult to achieve that, but if you want to get something remotely similar to a square wave, the rise time has to be less than 1/4th of the period.

0 Benjamin Mak over 11 years ago in reply to Avi Chami1

TI__Intellectual 2190 points

Albert,

Thank you for helping me out. With what you've told me, I now have a better idea of what device I will need.

Thank you!

Ben

0 Avi Chami1 over 11 years ago in reply to Benjamin Mak

Mastermind 7395 points

You are welcome!

I am glad I could help.

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[SN74AUC] Lighter Load Characterization