LT3042/3045 LTSpice simulation

[carlmart]

Does anyone know if there's an LTSpice simulation for a the LT3042 or LT3045?

I am trying to simulate it to regulate from 20v to 15-18v, but I am not familiar with the resistor values you need to use to set the output voltage.

When I input 20v I can't get the simulation to end.

 

[Indiglo]

At about half way down the product pages under Ltspice simulations are files for 3.8-20V to 3.3V @ 500mA and 3.8-20V to 3.3V @ 200mA.

Here are the links:

https://www.analog.com/media/en/simulation-models/LTspice-demo-circuits/LT3045_DC2491A.asc

https://www.analog.com/media/en/simulation-models/LTspice-demo-circuits/LT3042_DC2246A.asc

You can also find lt3042 and lt3045 demonstration files that you can play with (named 3042.asc and 3045.asc) hidden away in this ltspice windows directory:

"C:\Users\username\Documents\LTspiceXVII\examples\jigs"

 

[carlmart]

This the sim I made.

I want to have 18v at the output, but I don't quite understand how to do it.

 

[Mooly]

You have B and C shorted on your sim, also you have Vin set at just 5.5 volts. This is a linear reg and so needs at least 18v plus some headroom... which is getting toward maximum ratings for the chip. The voltage setting resistor needs altering to around 221k.

Its not an ideal application for this chip imo (your 18 volts requirement), in fact the data sheet specifies 15 volts as a maximum regulated output.

 

[carlmart]

Corrections made in the circuit.

OK. 15 volts then for output.

Which is the voltage setting resistor?

 

[euro21]

The inner CCS push 0.1mA current to SET pin, so there 150k represents 15V output.

 

[carlmart]

euro21,

Can you please upload that asc file?

Thanks!

 

[carlmart]

Would this PSRR curve be correct for that schematic?

The shape is quite weird.

 

[PRR]

> Would this PSRR curve be correct

-196dB is not creditable in a real-world circuit. It "might" happen through lucky cancellation, but don't bet on it. Or expect to real-life measure (or hear!) it.

>100dB is creditable, in a simulation, although real life parasitics will spoil this.

 

[carlmart]

How do you setup things correctly to simulate PSRR, impedance and noise on an LT3042 regulator?

Can anyone show it, if possible including asc files?

 

[euro21]

euro21,

Can you please upload that asc file?

Thanks!

There it is.

 

[carlmart]

There it is.

Thanks.

I can't seem to run PSRR and impedance simulations.

Do you know how to set things up for it to run?

 

[euro21]

Thanks.

I can't seem to run PSRR and impedance simulations.

Do you know how to set things up for it to run?

PSRR: run "AC Analysis" with 1V AC input. The result is the output.

Output impedance:
Delete input AC amplitude.
Run "AC Analysis" with 1V AC in current source (Advanced-AC amplitude=1) -as load-.
Plot output voltage. Plot current source current.
Retype V(v+) to V(v+)/I(I1).
Set left vertical axis to linear.

 

[carlmart]

OK, could run the impedance simulation.

Why does it take so long to run? Is there something that could be done for it to run faster?

In other power supply simulations I am doing now the run time is just a few seconds, almost instantly. Why here is different?

Can you feed a negative voltage to have negative output regulator?

 

[euro21]

Can you feed a negative voltage to have negative output regulator?

 

[carlmart]

These curves are based on simulations I did, with regulators based on the datasheet.

So the schematics have some more parts than those that are used by DIYINHK.

Perhaps someone can explain me why the differences or the parts missing from the DIYINHK design.

As I didn't quite like the ascending PSRR curve, I am now simulating that adding a CRC filter at the input, with remarkable results.

 

[carlmart]

Here's a PSRR comparison of the same LT3042 regulator above, just adding different CRC combinations.

Look how things get extremely better than with using just a single capacitor filter.

 

[arpagon]

When doing these simulations, the first electrolytic capacitor (connected to the voltage source) is useless except if you define some series resistance of this voltage source, just try .
Of course in the real life the things are different...

 

[sq225917]

Also worth noting that the more voltage you drop the quieter the output. IIRC 3v is the optimum drop.

 

[arpagon]

These curves are based on simulations I did, with regulators based on the datasheet.

So the schematics have some more parts than those that are used by DIYINHK.

Perhaps someone can explain me why the differences or the parts missing from the DIYINHK design.

As I didn't quite like the ascending PSRR curve, I am now simulating that adding a CRC filter at the input, with remarkable results.

BTW, I do not see any kind of load on the first picture?