SN74HC191: What is the internal impedance or the pull-up / pull-down resistance value?

Hello otake,

The internal resistance for the output pins  Qa-Qd can be calculated using the datasheet as follows.

Using the VOH voltage and IOH current from the electrical characteristics section of the datasheet

We can calculate a output impedance using R = V/I as (VCC - VOH)/ IOH
So this gives a impedance of (4.5-3.84)/.004 = 165 Ohms at (4.5Vcc)
You can recalculate this value based on the Vcc you are using.

For the input impedance, that can also be calculated from the datasheet using the digital input leakage specification and calculating R=V/I

This is for the CLK, /LOAD and /CTEN Pins

R = (6V/1uA)
R = 6 Meg Ohms

This is the minimum impedance, it will likely be higher than this and can be recalculated with the typical values for the current shown in the table.

Thank You,

Karan

Hi Karan,

Thank you for your answer.

It is very easy to understand with detailed answers, Thank you.

otake.