AVC logic family dynamic output control function

Craig Neely

Other Parts Discussed in Thread: SN74AVC16T245, SN74AVCA164245

Hi,

I'm curious about the dynamic output control (DOC) circuit discussed in the AVC technology guide SCEA006A.

My question is: do all members of the AVC family have this function? Only a few devices in the family have data sheets that mention it.

For instance -- I'm trying to select a 16-bit level-translator / buffer for my project. The SN74AVCA164245 datasheet mentions the DOC function, while the newer SN74AVC16T245 does not.

The SN74AVC16T245 otherwise seems to be a "better" version of the SN74AVCA164245 -- reduced tpd, reduced leakage, but I'd like to use the DOC circuit if possible.

In my application, I'm using the translator/buffer to drive a fairly long line (about 15cm), at a maximum of around 25 MHz (it's an HPI port on a TI DSP). As the DOC circuit has variable impedance, can anyone give some guidance as to the controlled impedance I should shoot for on the trace to minimize reflections? Ie. what is the nominal driver impedance in the high-drive / low-drive states?

Thanks for the help,

- Craig

over 16 years ago

0 Chris Cockrill over 16 years ago

TI__Mastermind 46480 points

Hello Craig

Only the AVCA and AVCB translators have DOC. The newer ones (AVC2T, AVC4T, AVC8T, etc.) do not.

0 Craig Neely over 16 years ago in reply to Chris Cockrill

Intellectual 290 points

Hi Chris,

Thanks for the reply. Do you know why DOC was left out of the newer devices? Ie. any disadvantages I should be aware of?

- Craig

0 Chris Cockrill over 16 years ago in reply to Craig Neely

TI__Mastermind 46480 points

H Craig I dont know the answer as to why. I suspect it is just another option. The DOC can cause issues if heavily loaded because the drive is shuts off early on the edges. If you have overshoot and undershoot issues it can be very helpful. If I was designing a circuit I would test both options.

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AVC logic family dynamic output control function