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
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice
480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at
http://www.analog-innovations.com | 1962 |
Remember: Once you go over the hill, you pick up speed