SN74AVC32T245: Output impedance, DOC circuit

All AVC devices have DOC.

You can derive the output impedance from the slope of the curves in figures 1 and 2. Anyway, the description of figure 5 and FAQ 7 list them:

In the high state, the output R_ON varies from approximately 50 Ω in the high-impedance mode to approximately 30 Ω in the low-impedance mode. In the low state, the output R_ON varies from approximately 50 Ω in the high-impedance mode to approximately 20 Ω in the low-impedance mode.

But why do you want to know the exact value of the output impedance? Usually, what matters is how much current you have to charge the capcitance of the load.

Hello Ryuji-san,

I have also sent an email with some additional details to your local TI contact, but I wanted to comment here as well. The output impedance of a logic device isn't constant while the output changes from low to high. You can look at it as a single pFET connected from Vcc (source) to the output (drain), and the gate tied to 0 V (for the sake of HIGH logic level output impedance calculations).

Your equation is correct, and what you show on the graph looks to be correct as well, however the calculation of 58.3 ohms doesn't give you the output impedance during the transient -- it gives you the maximum output impedance in the DC output state.

Unfortunately, we cannot guarantee a specific output impedance for all devices - this will likely change some from one lot to another, however you can be certain that the maximum you calculated will not be exceeded.

Can you tell us why you need this value? Typically impedance matching with logic is not necessary, and if we know more we might be able to help.