I think that one of the last things I'd trust SPICE for would be as an indication that a chip really could run faster than its rated speed, at least if the chip model came from the vendor.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Particularly since LTspice switcher models have a high behavioral content, rather than being modeled at the device level. That lets them certainly simulate faster. I can't comment on their accuracy... that's _very_ dependent on who wrote them. ...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 |
The only thing bipartisan in this country is hypocrisy
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
You don't even need LM339's.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
I think that, were I tasked with writing a bunch of models for a bunch of chips, that my main goals would be (a) make them never crash, (b) obfuscate or outright hide the inner workings of the chip, and (c) make them accurate _over the specified operating range_.
Given (c), I wouldn't hesitate to publish a model that failed to predict correct _or_ incorrect operation if the chip were operated will outside of it's limits -- I'd probably aim for at least 50% out of range at room temperature, but if a customer tried to predict the behavior of a 100kHz part at 200kHz, I'd have some really nice, diplomatic way of saying "you're screwed, get over it". In fact, it'd probably be in the app notes for the models.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
One thing that would be wise, but is rarely included... power supply ramp-up. Having been burned mightily with a chip with both positive and negative supplies, I make a point of simulating power ramp-up and sequencing... then adding local protections, as needed, into the chip design.
Most behavioral models don't do that adequately.
I'd like customers to come to me with their device-level circuitry and ask for a behavioral equivalent... but they won't. Somehow they think I'll steal their IP. It generally isn't worth stealing :-) ...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 |
The only thing bipartisan in this country is hypocrisy
The model is from ON Semi and I am not running the chip above its rated speed while in regulation. It's actually working (on the simulator) with a 68uH inductance and well within normal timing limits. All I was wondering is why the datasheets and app notes always prescribe higher inductance values.
But you are right about models being suspicious. It does one thing it ain't supposed to be doing and I still need to get to the ground of that via the LTSpice group (this sim was with 200uH though):
App notes and the internal schematic of the chip says that the feedback comparator can never terminate the switch during a cycle (positive dark blue ramp). And here it does just that ...
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Is the model in text format or is it encrypted? ...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 |
The only thing bipartisan in this country is hypocrisy
The Intusoft version is in plain text. I think this is it, along with an X1 call. It's not exactly what I expected to see. E.g., who's Kehinde Omolayo? Hmm, Magnetico, Inc. Hmm, 2003, "Standex International Corp. has purchased substantially all of the assets..."; the trail grows cold.
X1 7 4 5 0 8 6 7 7 MC34063AX2 { } .SUBCKT MC34063AX2 1 2 3 4 5 6 7 8
*exempt 20030227 20395 -30736294 *BY KEHINDE OMOLAYO 2-20-03 *TERMINAL ID *SWITCH COLLECTOR=1 SWITCH EMITTER=2 TIMING CAPACITOR=3 GND=4 *COMPARATOR INVERTING INPUT=5 VCC=6 IPK SENSE=7 DRIVER COLLECTOR=8 .MODEL DMC34063 D (CJO=2P N=0.05) .MODEL QSWITCH NPN BF=75 CJC=2P IS=3E-9 RB=1 RC=0.45 RE=0
--
Thanks,
- Win
Thanks, Win! I'll try to pick it apart when I have a free moment. Most of those behavioral games are less than adequate... particularly those IF..THEN..ELSE statements :-( ...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 |
The only thing bipartisan in this country is hypocrisy
There's actually three more models around but they essentially behave similar. Thing is, the chip is not supposed to turn off the switch during the positive ramp because the comparator does not tie into the reset input of the register, only the set input.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
[ snip ]
What, you analyzed it in two minutes? I have to make a schematic drawing from the spice net list, and analyze that.
--
Thanks,
- Win
=3D8
2Yeah. I read TI's app note. So it can start an ON cycle any time during ramp up, but can't ever stop until ramp-down. Crude. Burp, sputter, and cough, in this application.
-- Cheers, James Arthur
No, I am scratching my head about this a bit longer than two minutes, tried various models, etc. :-)
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Well, if it did that I'd be happy. But it does cut during ramp-down and according to the internal wire-up it's not supposed to. Helmut Sennewald, one of the LTSpice gurus, could not reproduce the error I saw. Sent him my file, so we'll see.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
My first switcher was a hysteretic 24 to 5 buck, for a military control system, the engine room controls for the LHA helicopter assault ships. I used an uncompensated uA709 as the comparator, driving a 2N2905 PNP, driving a 2N3055 emitter follower. The 3055 didn't saturate so was pretty fast. I ran it at 22 KHz because I could hear 20K in those days. I used a schottky catch diode, which was pretty radical in those days.
A few years later, the Navy ripped the system out and replaced it with pneumatic controls, because they couldn't find people who could maintain it.
John
It's s'posed to cut off during ramp-down--that's when the flop gets reset, unconditionally. So says TI, anyhow.
the operative paragraph being the last one pg. 5. And, the last comment in Table 1 confirms:
"Output switch conduction is always terminated when Ct is ramping down."
-- Cheers, James Arthur
Will you PLEASE learn how to FRIKKIN learn how to snip?
PLEASE I really appeciate your responses, but I'll be damned if 'll scan down three or four pages to find your answ3r
Thanks
Jim
Funny that RST can't learn how to FRIKKIN learn how to bottom-post.
John
[snip]
RST? I block RST :-) ...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 |
The only thing bipartisan in this country is hypocrisy
I know but as shown in my sim plot if is terminated before Ct is ramping down. That not s'posed to happen. But does, at least according to SPICE.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.