On 3/24/2011 12:33 PM, Bitrex wrote:
On 3/22/2011 7:01 PM, Jim Thompson wrote:
On Tue, 22 Mar 2011 17:01:45 -0500, John Fields
wrote:

On Fri, 18 Mar 2011 22:46:48 -0400, Bitrex
wrote:

On 3/18/2011 7:13 PM, Jim Thompson wrote:
Got annoyed at the flaky 555 models that are out there, so I rolled my
own...

http://www.analog-innovations.com/SED/MyLMC555.zip

Based on old AMI 20V CMOS device models, mostly form/fit/function with
CMOS, but some behavioral on the front-end where it doesn't matter.

Optimized and fitted to National LMC555 at 5V operation. It'll work
at other voltages but may sink/source more or less than spec at other
voltages because of ancient 5u devices :-)

Try it out and let me know.

...Jim Thompson

Hi Jim,

Thanks for taking the time to create this model. I was doing some
experimenting with it and comparing it to the standard bipolar 555
model, and noticed that the CMOS model seems to have significantly
greater shoot-through current than the bipolar model. I haven't used a
CMOS 555 or measured those currents "in real life", so I'm curious if
that is a real difference, or perhaps the bipolar 555 models don't
model
it effectively?

---
Notice that the shoot-through current for an ICM7555, in real life, as
indicated on page 6 of:

http://datasheets.maxim-ic.com/en/ds...55-ICM7556.pdf

is very small compared to that from the bipolar 555, so there's either
something wrong with Jim's model, or you're making an error of some
kind.

---
JF

I sized my CMOS devices based on source and sink current of the output
at VCC=+5V for the _LMC555_ chip... Intersil datasheet was used only
for structural ideas.

I simulate 7-8mA "shoot-thru" depending on direction of transition.
Which, for CMOS with considerable source sink capability, seems pretty
normal to me. Width at the 50% point of overlap current is 8.5ns,
TF/TR at output ~ 7.3ns

What does "...significantly greater shoot-through current than the
bipolar model" mean?

...Jim Thompson

Sorry for the delay in my reply, I didn't realize the thread was still
active. Here's what I get using LTSpice with the test circuit:

http://i227.photobucket.com/albums/d...ex2007/555.jpg

The pulses appear to be about 100 ns wide. It probably is really better
than the bipolar 555, because looking at the graph on the Maxim
datasheet I don't believe the bipolar 555 model included with LTSpice is
modeling the supply spikes accurately.

My mistake, I think the pulses are shorter than that. It's a little
tricky measuring them in LTSpice.