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TLC555-Q1: Usage question

Koji Ikeda
Expert 5325 points
Part Number: TLC555-Q1
Other Parts Discussed in Thread: NE555

Hello Support team,

I receive some questions for TLC555-Q1, could you support?

*On excel calculation sheet, what Vd(column N18) means?

*TLC555-Q1 output is push-pull. Why application circuit on datasheet uses pull up resister?

*On excel calculation sheet, why diode is recommended with lower than 50% duty?

*What kind of diode does TLC555-Q1 recommend to use? Or please shows TYP forward voltage value of diode on excel sheet.


Thanks,
Koji Ikeda

  • 0
    TI__Guru*** 139906 points

    Hello Koji-san,

    • Cell N18 is the expected variation in the diode forward voltage. The diode voltage varies with temperature at roughly -2mV/C (not covered by tool). The diode voltage also varies with the logarithm on the current flow. At high current the bulk resistance also matters. I don't know if the tool considers these factors. 
    • Pull up is not needed. That resistor is just a copy and paste from the NE555 timer. The NE555 is also push pull , but it has a higher push headroom voltage 
    • High time has a resistor factor of (RA+RB) and low time has a factor of (RB). Clearly (RA+RB)>(RB), so high time is greater than low time; that is >50%
    • Try my favorite small signal diode, 1N4148

    Check out [FAQ] How do I design a-stable timer, oscillator, circuits using LMC555, TLC555, LM555, NA555, NE555, SA555, or SE555?

    If you tell me the desired frequency and duty cycle, I will will provide initials value for the timing components.