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SN74LVC1G123: Using SN74LVC1G123 to generate pulse duration of 0.1us, 0.2us, 0.5us, 1us, 5us and 10us

Part Number: SN74LVC1G123

Hi TI team,

Appreciated that if TI team could help to confirm that by using Cext = 30pF and potentiometer, Rext from 1kohm to 100kohm can be used to generate the pulse duration of 0.1us, 0.2us, 0.5us, 1us, 5us and 10us.

What are the other factors that may affect the accuracy of the pulse duration ?

Thanks in advanced. 

  • There are five things that will affect the output pulse width of the device if they vary:

    (1) Supply voltage

    (2) External timing capacitor, C_ext

    (3) External timing resistor, R_ext

    (4) Temperature

    (5) Manufacturing process

    1 through 4 are dependent on your system, while 5 is not.

    Temperature can cause up to about 2% of variation from our device, however typically the capacitor will have the largest temperature coefficient and will cause the most variation (some can cause greater than 100% variation).

    The application report "Designing With the SN74LVC1G123 Monostable Multivibrator (Rev. A)" contains this plot that is from a similar configuration to what you are considering:

    Supply voltage variations can cause K to change, and at 3.3V with a 30 pF timing capacitor, K is relatively large and will vary significantly. I do not have data to provide for this capacitor / supply combination. I would recommend including supply variations as part of your prototype testing prior to building a complete system.

    Manufacturing process could cause some variation depending on many variables. Unfortunately, our data doesn't isolate this, so I have to discuss this in a more holistic sense.

    Looking at our char data, across supply (10%), temperature (-40 to +125C), and process (weak, nominal, strong), the worst case would be a variation of 15% in the output pulse.

  • Hi Maier,

    Thanks for your reply. The product is tested at room temperature, ~24'C. 

    Below is the table that I have calculated. It is included the Rext and Cext tolerance (but not included voltage supply variation). The pulse duration generated is ~+/-19% variation.


    Rext (+/-10%)

    Cext (+/-1%)

    Pulse width min (us)

    Pulse width max (us)































    If take rid of temperature change, what is the variation in the output pulse can be estimated ? The voltage supply is from 3.3V PCIe Gen4. 

    Can the 3.3V PCIe affect the output pulse ?

  • And the capacitor I used is Multilayer Ceramic Capacitors MLCC - SMD/SMT 50V 30pF C0G 0402 1%.

    What is the concern using this type of capacitor ? 

  • the output of the pulse is connected to NPN to level shift up to 12V. May I know any concern for the output pulse duration ?

  • Is there a reason you didn't measure the value of each R and C as you tested them to determine the actual K value and impact of the IC? If you're trying to determine the amount of change due to different components, then this would be a critical step.

  • Hi Maier,

    I have calculated the Rext and Cext based on the leverage of Table 6.8 in datasheet. 

    I will measure each of R and C when i have received the board. 

    I will use fixed 30pF +/-1% tolerance and varies with rheostat to have different Rext to produce different pulse duration as shown in the table i attached above. 

  • I understand -- these are not tests you have completed, but your test plan.

    The type of capacitor can have an impact on the K factor, but that's why we recommend to prototype the build before finalizing your design. We don't have any data on capacitor types vs K factor.