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I want to use a 555 as a one shot retriggerable using its monostable configuration.

Reading the datasheet of say TLC555 LinCMOS, I was not able to find the value of the voltage divider consisting of the 3 R resistors in the diagram below.

555

I want to change at which voltage the trigger will occur by applying a voltage to the CONT pin. Can I use a voltage divider (between VCCand GND) there? I think it will be dependent on the value of R.

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  • \$\begingroup\$ You can even over drive the CONT input above the nominal 555 supply, provided the internal divider drops it to be at or below the nominal supply value. Note that to determine the internal divider voltages (on each comparators) you do need to account for the first internal R resistor (connected at VCC). \$\endgroup\$
    – Nedd
    Commented Apr 20, 2023 at 23:28

1 Answer 1

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They are all equal, producing nominal thresholds of 1/3 and 2/3 Vcc.

In the original bipolar 555, they were 5 kΩ each. In the CMOS version, they're larger — this datasheet says 100 kΩ.

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  • \$\begingroup\$ Thanks, I read this datasheet and didn't found the info. Could you give the page number where you found it ? Typing Ctrl + F and 100 didn't return anything relevant. \$\endgroup\$ Commented Apr 20, 2023 at 22:31
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    \$\begingroup\$ Look at the two images top of Page 3. Not everything is searchable. Also keep in mind the wide tolerance of many resistors on IC chips, they may be well-matched to each other but the tolerance may be worse than +/-30%. It is not specified in any datasheet I've seen for the 555. \$\endgroup\$ Commented Apr 20, 2023 at 23:01

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