TLC555: Strange Simulation Results

Antenna_Head

Genius 12780 points

Part Number: TLC555

Tool/software:

I am simulating the following very simple, well known circuit for a ~50% duty cycle waveform. TINA file attached.

At startup, there is a strange long delay of about 12 ms before the device begins to switch:

I've looking into the subcircuit, and this appears to be a transistor level circuit.

This behavior isn't realistic- it should start clocking pretty much right away, stabilizing after about 1 ms when the capacitor on the CONT pin stabilizes.

Can you please review this model and explain what's going on here?

TINA file attached.

Thanks!

-Steve

555 astable.TSC

over 1 year ago

0 Alex Curtis over 1 year ago

TI__Intellectual 2670 points

Hi Steve,

It looks like this is an issue with the transient simulation settings. When running the transient simulation, selecting "zero initial values" instead of "calculate operating point" results in the expected behavior.

555 astable working.TSC

Best Regards,

Alex Curtis

0 Antenna_Head over 1 year ago in reply to Alex Curtis

TI__Genius 12780 points

OK, that's interesting.

As you can see in the schematic, I have the initial conditions for the the capacitors set to 0, and the 12V source is a step, starting at 0V at time=0. So, everything SHOULD be zero to begin with anyway using the operating point at t=0.

Weird.

Thoughts?

-Steve

+1 Alex Curtis over 1 year ago in reply to Antenna_Head

TI__Intellectual 2670 points

Hi Steve,

Apologies for the delay. It's hard to say for certain why the behavior in the transient simulation is different. When you run with "calculate operating point", it appears that TINA might overwrite the conditions you've set on individual components. However, setting the transient simulation to "zero initial conditions" results in the expected output.

Let me know I can help with anything else,

Alex Curtis

Clock & timing

Clock & timing forum

TLC555: Strange Simulation Results