Hi, I'm trying to design a circuit that makes an IR LED flash in short 56.8kHz pulses (50% Duty cycle) few miliseconds. To do this I am using two LM555 timers, one at 384 Hz and the other at 56.8kHz, with the output of the slower connected to the reset of the faster one. I can get the slower one to work fine, but I cant seem to get the faster one at exactly 56.8kHz in simulation (I've been using LTSPICE and Multisim) or on a board. the configuration I'm using is the "50% Duty Cycle Oscillator" at the end of the data sheet with R1 = 12700Ω, R2 = 5370Ω, and C = 1nF. I'm pretty sure of my values and used mathcad to check them. Whenever I test it I always get results that are about 3kHz low. I realize that the actual chip has some small current draw and capacitance, but i don't understand why the simulation would be wrong if the model is supposed to be ideal. My guess is that there is some capacitance in parallel with the external capacitor that throws it off, but the datasheet doesn't give information on the chips capacitance. I would like to be able to find the source of the problem so that I can rewrite the equations to get a more accurate result. I'm not very experienced with this kind of thing yet so any help would be tremendously appreciated.
Thanks!
http://www.national.com/ds/LM/LM555.pdf (Data sheet)
http://i.imgur.com/Q6dkP.jpg (screenshot of the Circuit)
Thanks!
http://www.national.com/ds/LM/LM555.pdf (Data sheet)
http://i.imgur.com/Q6dkP.jpg (screenshot of the Circuit)
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