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I want to know if the pulse period of the monostable multivibrator using NE555 can go down to around 200ns. I don't have necessary equipment to test it and I'm afraid the timer can't work with that short pulse. The high and low threshold is 2.4V and 0.8V, so the pulse period starts when the timer output rise reaches 2.4V and ends when it gets down to 0.8V.

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    \$\begingroup\$ You'd need to refer to the datasheet of the specific version of NE555 you want to use, from the specific manufacturer of that part. There are so many different "555" devices out there - everyone and their cousin makes one. If you look at the datasheet from TI you'll that their examples & tables don't show much of anything less than 100us, and the output characteristics show typical rise and fall times are typically 100ns so even if it could produce an 200ns pulse, the shape of the pulse would be more like a single sawtooth. \$\endgroup\$
    – brhans
    Mar 5, 2022 at 17:19
  • \$\begingroup\$ @brhans the part that I used is NE555P-ND, I found the datasheet from TI but it only have general information, I don't see any thing about like rise time, fall time, ect. so I can't really sure \$\endgroup\$ Mar 5, 2022 at 18:02
  • \$\begingroup\$ You can make a one-shot on any transition with just an XOR gate direct and via an RC, then AND gate if you want just rising edge trigger. for pulses > 1~2ns to > 1 s \$\endgroup\$ Mar 5, 2022 at 18:50

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Even the faster CMOS types seem like they'd be marginal at best, based on the maximum frequency and worst case rise and fall times. 555 timers are not really aimed at that kind of speed, they're more slow-witted muscular drivers.

Maybe you can consider a monostable such as 74HC123 which are well-specified in that range. Looks like 2K and 100pF is about right. Maximum recommended power supply is in the 5V range, however, and they don't have hundreds of mA drive capability.

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  • \$\begingroup\$ I did think about the 74HC123 but the input signal is from another 555 astable clock so the 74HC123 may cause a bit of issue on driving it. The astable can't go down to 200ns since it have to drive another chip and the pulse time need to be 500ns. \$\endgroup\$ Mar 5, 2022 at 17:54
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    \$\begingroup\$ @SairextIrkaris what kind of application needs pulses that are < 1µs long, but is still OK with the total lack of accuracy that a 555 has? this all screams that you're trying to solve a more complex problem, and you thing a 555 is the solution, so you ask about that, instead of telling us about the actual problem you're solving. The 555 is not appropriate here. Full stop. \$\endgroup\$ Mar 6, 2022 at 13:38
  • \$\begingroup\$ @MarcusMüller I to avoid clock conflict with the interrupt signal, the high period is around quarter of the clock period, the clock frequency is 1.25MHz so the clock period is 800ns and a quater of it is 200ns, this will help the clock to not send the signal too fast lead to the chip on the board can't detect the signal in time. \$\endgroup\$ Mar 7, 2022 at 7:15
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    \$\begingroup\$ OK, none of this is a use case for a 555, and certainly not for a NE555. \$\endgroup\$ Mar 7, 2022 at 9:51

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