TLC555 Design Calculator

Semiconductor Integrated Circuits (ICs)
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1

Hello everyone,
I need to generate a square wave at 600kHz with the TLC555. On the datasheet (7.3.2 Astable Operation) TI advise us to use there calculation tool for the frequencies above 100kHz. So I download it and I introduce the value in the tool for the calculation : Vcc = 5V , C1 = 0.1n , Freq = 600kHz , Duty Cycle = 50% , and I check the box “Use Diode?” (for the ~50% duty cycle)

Calculator
Calculator1011×444 64.5 KB

After that I introduce the value calculated in a Spice simulation (I use “PSpice for TI” and it should had the best spice model for the simulation (the encrypted one))

TLC555

TLC555_sim
TLC555_sim1366×618 143 KB

And the problem is that the result of the simulation don’t match with the calculation design tool ! and I don’t understand why … Is my simulation wrong ? is the TI tool’s wrong ? is the model of TI wrong ?
So if someone can help me I will be very grateful ! 'cause I can’t find the answer :confused:
Thank you very much !!

2

Greetings,

I suspect the discrepancy is related to the diode used; it’s characteristics have direct bearing on the timing properties of the circuit, and insofar as the spreadsheet tool offers no input for diode specifications, it’s apparent that some assumptions are being made.

If a 50% DC is what you’re after however, the old National 555 datasheet suggests a circuit of rather simpler character:
image

In any event, I’d suggest trying PbSnSpice v.6040 when questions about simulation models arise. It can be a bit slow to converge, but the results are quite reliable…