How do I simulate op amp supply current in Ltspice?
I think I pick level 3a but I don't know the parameter name for the supply current.
D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design
"D from BC" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...
Hello D from BC,
I think you talk about the quiescent current. Just add a resistor between V+ and V- for every opamp in your schematic.
If you want do that in the model file, you have to save it with a different name. This would require a modified symbol too.
Best regards, Helmut
It's a bit rough, but might do. Thanks..
D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design
Many manufacturers do not accurately supply current. That includes Linear Technology. I wanted to monitor current using a LT1097 (if memory serves) low power amplifier as a comparator and "measured" something like 13ma into the V+ and V- terminals.
When I complained about this to Mike Englehardt's department I got the excuse "we don't model supply current" and also, "don't use an opamp we have comparators".
I thought their reply was pretty lame.
Bummer :( Oh well.. I'll have to make do.. Thanks
D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design
Pardon me, it was about a year ago and my memory is foggy. I don't want to be unfair to LTC.
They probaby said "... don't always model supply current for opamps". Not always. Or more probably it was something like "... not modelled for use as comparator". I forget exactly, so it was wrong for me to try and quote what I don't accurately remember.
In all fairness, I did not breadboard the circuit. For all I know the LT1097 (and a handful of other opamps I tried) might actually draw +/- 13ma when used as a comparator.
But, I decided to use a comparator. Supply current can often be measured just like Helmut stated, but not always.
Power supply currents are tricky to model for simulation. It's easy enough to include load currents, but currents flowing in compensation capacitors can have some pretty wild behavior.
The only real way to do a behavioral model properly is to start with a device-level netlist, then match behavioral to device-level.
I get calls all the time about modeling with two consistent results:
(1) The semiconductor company won't share the "real" netlist, wanting modeling from the data sheet... what a crock, and...
(2) They expect it to be done for virtually free.
Thus I haven't ever done any commercial modeling... just for my own internal use where I already have access to an accurate netlist, and process library.
I'm considering model generation on the side, _as_I_can_get_to_it_ ... free... for non-commercial use.
Might be good advertising and get me some design jobs ;-)
What would people like to see modeled?
...Jim Thompson
--
| James E.Thompson, P.E. | 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 |
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I love to cook with wine Sometimes I even put it in the food
A LMV431 shunt regulator?? :) It can be modeled with an op amp that draws about 100uA of quiescent current.
D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design
Ask and yee shall receive... actually done back in 2002 ;-)
.SUBCKT LMV431 R A K
** by Jim Thompson, © 2002-2009 ** R_R1 N_1 N_2 0.25 E_BUF1 N_3 0 R 0 1 R_R7 N_3 A 1Meg V_V1 N_2 A 1.24V D_D1 A K D1N4148 F_F1 K A VF_F1 1 VF_F1 N_3 N_1 0V .ENDS LMV431...Jim Thompson
--
| James E.Thompson, P.E. | 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 |
I love to cook with wine Sometimes I even put it in the food
Neato..
D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design
Hi Jim, I remember several requests for modeling of supply current 'back in the day' and it always got the same reply - healthy laughter!
Same as modeling tants for their more emphatic behaviors... 8-)
Charlie
In a way, modeling power supply current shouldn't matter, _provided_ there is adequate bypassing.
But, in my chip designs, I'm always checking that because micro-power seems to be the watchword today.
...Jim Thompson
--
| James E.Thompson, P.E. | 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 |
I love to cook with wine Sometimes I even put it in the food
...Jim Thompson
Ah, but you see, there is this one trick, where you feed the power supplies via a small resistance, and then connect transistors to the power supply pins to build a higher power opamp out of the chip, However, since almost none of the opamp models actual reflect the true, tranisient nature of the current draw on the chip, you can't model this in PSpice, you have to breadboard it and try to get the bias right.
Charlie
Yep. I recall first using that 'trick' around 1970 ;-)
...Jim Thompson
-- | James E.Thompson, P.E. | 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 | Bill Clinton also had a Stimulus Package. Her name was Monica.
How do you assure adequate bypassing? How do you get the power grid right? Package? Someone has to do all that rot.
Mega-power (130W processor - 3GHz) is also a problem. There is a ton of power distribution simulation done on logic ASICs.
"Charlie E." schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...
Hello Charlie,
I have made a subcircuit which reflects the output current to the supply voltages. You can download it from the LTspice Yahhoo group. There is the model, symbol and an exmple in this folder.
Files > Lib > Opamp Load Curr. From Supplies
.SUBCKT xopps in out psp psm vgnd
That's fine if IQ is a constant, relative to output swing... not accurate for most OpAmps I know of, plus you have compensation capacitor slewing currents in the real world.
...Jim Thompson
--
| James E.Thompson, P.E. | 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 |
I love to cook with wine Sometimes I even put it in the food
"Jim Thompson" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...
Hello Jim,
"A bird in the hand is worth two in the bush."
Best regards, Helmut
[snip]
Of course ;-)
I do pretty much the same as you, except I merge it into the OpAmp model, avoiding the "{IF(..." crossover.
As I've said before, _accurate_ modeling of PS current is not trivial.
...Jim Thompson
--
| James E.Thompson, P.E. | 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 |
I love to cook with wine Sometimes I even put it in the food
If anyone remembers the old LH0002 buffers you could try a subcircuit that is similar. .
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