# SN74AUC74: Output resistance of SN74AUC74 and SN74AUC1G74 (Q and Q-INV)

Part Number:SN74AUC74Other Parts Discussed in Thread:SN74AUC1G74,

We did not find the output resistance of SN74AUC74 and SN74AUC1G74 in their datasheet. Please help us confirm the value. Thanks a lot.

##### Kailyn Chen：

The output impedance can be derived from the VOx/IOx values .See FAQ:, we could found that the output impedance will depend on the supply voltage. For example, VCC=3V,Voh=2.3V, Ioh=24mA , then Rout= (Vcc-VOH)/IOH=(2-2.3)/0.024=29.167ohm.

https://e2e.ti.com/support/logic-group/logic/f/logic-forum/742466/faq-what-is-the-output-voltage-voh-or-vol-when-the-output-current-is-x-or-the-supply-voltage-is-y

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##### Clare Zhang：

Thanks. We shall use SN74AUC74 and SN74AUC1G74 with VCC=2.5 V. But there is no parameter that is related to VCC=2.5 V. Could you help us to find the paramater?

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##### Kailyn Chen：

I am so sorry we didn't have the detailed Voh and Ioh with VCC=2.5V,  but we could  calculate approximately:

when VCC=2.3V. Voh=1.8V which is about 78%VCC, when VCC=1.65V, Voh=1.2V which is about 73%VCC. If we used 78%VCC, VCC=2.5V, then Voh is about 1.95V or 80%VCC is 2V, similarly, the output current is higher than VCC=2.3V, we could use =10mA, so we could calculate the approximate value:

Ro=(2.5-1.95)/0.01=55ohm.

That it to say, the output impedance is about 55ohm with 2.5V power supply, but unfortunately, we didn't find the specified value about this, but I think it could use 55ohm to evaluate the IC function. • QQ咨询
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