I have recently downloaded a datasheet for one of the chips I am using in my project, the familiar 74HC164 shift register. The datsheet URL is here:
So I then look inside it to try to figure out how long the chip needs to process various states, and it provides three temperature categories as circled in the picture:
Since my circuit never overheats, and runs in a normal room temperature environment, I find this particular datasheet confusing. It's because my scenario fits two temperature categories and possibly three. To me, room temperature is 21 degrees, so the only category that MIGHT not apply to me is the 25 degrees celcius category.
Let's say I wanted to determine Propogation delay based on the information given. What value should I use?
- The worst case of 255ns (because the temp range is -40 to +125 degrees)?
- Do I need a special (tell me its not expensive) thermometer to measure the degree range of my chip while its running and get results based on the temperature range that special thermometer reports?
- I should assume these temperatures mean the maximum rise temperature of the circuit when it is running and follow the 25 degrees column?
Or is there another way to calculate the value based on the chip not warming up at all even with the correct power applied to it and the whole circuit being in a room at room temperature?