Timeline for What's the purpose of this resistor into a NOT gate?
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 23, 2020 at 22:48 | vote | accept | donturner | ||
| Apr 22, 2020 at 15:26 | comment | added | Spehro 'speff' Pefhany | I would say "current-limiting resistor" or "protection resistor" depending on whether it's intended to be deliberately driven outside the range. My ca. 1970 First Edition McMOS (Motorola) CMOS Handbook does not use a consistent term, but refers to them. The maximum value is limited by leakage from the input (and PCB), typically worst at maximum temperature (specified as 1uA max), and by how much you can allow the input to be slowed due to input capacitance (15pF max). So 1uA * 330k = 0.33V. The 1uA is also a very loose spec (typical is much less). | |
| Apr 22, 2020 at 15:14 | comment | added | donturner | Thank you. Is there a common term for this resistor, like "current limiting resistor" or "protection resistor"? And how would one choose a suitable value for it? | |
| Apr 22, 2020 at 14:31 | comment | added | Spehro 'speff' Pefhany | Yes, spark over or arc. It depends what the resistor construction is like- a smallish 0402 or smaller resistor might be rated for 10-50V. only, and actually fail at a few hundred V. It is not unnecessary- it makes the input far more robust, but it's not necessary to functionality. Leaving off protection on a CMOS IC input connected to the outside world would be very bad practice generally. | |
| Apr 22, 2020 at 9:12 | comment | added | donturner | I think I understand. A very high positive input voltage might arc the 330k resistor causing the 4069 supply voltage to be forced to a "destructively high voltage". Could ESD do that? Are you saying the 330k resistor is probably unnecessary? (sorry for all the questions, really just trying to get a good grasp of audio circuit design) | |
| Apr 22, 2020 at 7:12 | comment | added | donturner | Sorry, what do you mean by "flash over"? | |
| Apr 21, 2020 at 22:36 | history | answered | Spehro 'speff' Pefhany | CC BY-SA 4.0 |