LM25037 Spice model

Simone Massimino

Other Parts Discussed in Thread: LM25037, LM5030

good morning this is my first post here on ti forum so i'm pretty sorry if is not the correct place.

Let's face the problem i'm currently designing an isolated dc dc with lm25037 but i'm having some trouble on the spice simulation, in particular connecting the optocoupler to the comp pin via a pull down network connected between ground and optocoupler collector which is basically right if i've understood the various paper i've looked to.

The problem is that nothing happend, current drive up to 40 mA on COM pin but voltage on that pin is still almost 5V
to check if design was right i used the model of lm5030 too and with that component isolated feedback works pretty good. The strange thing is that to check COMP(in another simple simulation) on lm25037 i tied it to ground via a 5k resistor, so since lm25037 has an internal pull up resistor of 5k COMP pin has to be at 2.5V right? but for some reason it's still clamped to almost 5V.

thank you for any further reply it will help me very much

over 10 years ago

0 Peter Meaney over 10 years ago

TI__Mastermind 31580 points

Hi Simone,

In the simulation is the FB tied to ground/0V of the IC?

Regards

Peter

0 Simone Massimino over 10 years ago in reply to Peter Meaney

Prodigy 70 points

Hi Peter,

Thanks for the answer, yes i've tied it to GND as suggested from datasheet

0 Simone Massimino over 10 years ago in reply to Simone Massimino

Prodigy 70 points

Here is the schematic of the interested part if is needed some informations more please ask me

0 Peter Meaney over 10 years ago in reply to Simone Massimino

TI__Mastermind 31580 points

Simone,

What happens if you put a current source to ground from the comp pin that ramps from 0 to 1mA?

Also what is voltage waveform on the SS pin during the time that the COMP pin is not behaving correctly?

The SS voltage should also affect the Comp voltage.

Thanks

Peter

0 Simone Massimino over 10 years ago in reply to Peter Meaney

Prodigy 70 points

the simulation is on te steady-steady profile Here is the new test circuit

Here is the comp voltage

Here is the current ramp on comp pin

here is Vss

And finally there is Vout that is purely indicative but the mean is that it doesn't stop on a value.

0 Peter Meaney over 10 years ago in reply to Simone Massimino

TI__Mastermind 31580 points

Hi Simone,

I have forwarded the post to our modelling team to see if they can run a quick test on the model to verify the issue.

Regards

Peter

0 Simone Massimino over 9 years ago in reply to Peter Meaney

Prodigy 70 points

are there any further news? thanks a lot

0 Peter Meaney over 9 years ago in reply to Simone Massimino

TI__Mastermind 31580 points

Hi Simone

I will chase this today with our modelling team, sorry for the delay

Peter

0 Simone Massimino over 9 years ago in reply to Peter Meaney

Prodigy 70 points

Hi again sorry but i've never heard any news.

I know i'm pretty boring sorry :)

0 Peter Meaney over 9 years ago in reply to Simone Massimino

TI__Mastermind 31580 points

Simone,

Sorry for the delay I have been travelling recently. Please send me your simulation files and our simulation will take a look at them and see what the problem is.

Regards

Peter