SN74HC595: What is the maximum clock frequency when Vcc=3.3V under 85 degree ambient temperature?

Hi Tony,

The max frequency range listed in the datasheet is of 2V 5MHz, 4.5V 25MHz, 6V 29MHz. These values are guaranteed and measured at a 50pF load over the entire operating temperature range including 85C. 

So assuming a linear relation between voltage and frequency and using the two external points of 6V and 2V, we see that at 3.3V, the device should have a max frequency of 12.8MHz. The actual max frequency should be higher than this because the relation is not linear but more logarithmic. However if your load is higher than 50pF, then your max frequency might be a bit lower.

I would say if your load is less than 50pF, the device should support 12.5MHz at 85C at 3.3V Vcc.

Thanks!

-Karan