LM5021-Q1: output error

Hello Shreyes,

Thanks for submitting this question.

Unfortunately I'm not able to access your google docs link due to our company security internet browsing policies.

Could you please share a screenshot or share the file directly as an attachment to this post?

I'll be happy to help you troubleshoot your LM5021-Q1 design.

Regards,

Andrew

new.TSC

Thank you for replying sir , this is my design plz have a look at it .

Hello Shreyes,

I don't see any glaring mistakes on your schematic.

Can you describe what exactly you mean here?

Shreyes Gedam said:

unable to get desired o/p

I assume that you're just simulating this design, what kind of analysis are you trying to run? What errors/results are you able to get?

If you have a physical design to test, then I recommend capturing startup (output voltage) and switching (drive circuitry) waveforms and sharing them to help narrow down the cause of your problem. 

Thanks for posting the schematic.

Regards,

Andrew

I triied running Transient response but instead getting output of 12V 1A I got a very low o/p in micro volts and I cant figure out why that is happening

TASK 2.rar

In above rar file i have attached my sim . Could you try and run it maybe you will find my mistake

Regards,

Shreyes

Hello Shreyes,

Please give me 24 hours to investigate the root cause of your issue further.

Regards,

Andrew

LM5021 Sim.rar

Hello Shreyes,

That's great you were able to produce the results you expected. 

My assumption is that it's due to the transistor macro you were using, it may not have been truly "bidirectional" and due to the body diode model.

If you'd like further clarity on how to use TI models/marcos, you can also try consulting this training series https://training.ti.com/tina-ti-tutorial?context=1127691 

Regards,

Andrew

Hi,

can you help me understand why IC is behaving this way ?

ss, Comp, Out, Vcc these pin have very low voltage but in fact according to data sheet they should be a lot higher than current values

I don't understand how it can work if ic isn't working bellow i have attached sim and also schematic .1856.LM5021 maybe.TSC

Hello Shreyes,

I'm sorry to hear you're still having trouble getting this simulation to behave how you expect.

But, try reversing the directions of your diodes labeled Daux and Dsnub.

It looks like you are getting the correct voltage and current at the output of the supply though.

Regards,

Andrew

Thanks for reply, reversing did nothing .

Yes although im getting output for this but when I try to get a different output its not behaving properly and I think the reason for that is Comp,VCC,VIN these pins are getting very limited supply . If the IC cant get enough power to start how can it perform . If you can redesign or spot any faults that would be huge help .

Hi Shreyes,

Thanks for trying my suggestion and letting me know we need to try something else. 

Can you describe what you changed to get a different output, or what load conditions you're trying to test? 

I think you're on the right track about startup issues affecting performance. 

Please give me 48 hours to investigate this further .

Thanks for your patience.

Regards,

Andrew

Thanks for replying 

For diff o/p I changed values of diodes,Txmer ratio/Lp, Cout & some resistors 

I don't understand the behaviour of IC , looks like all connections are ok still it has startup issues . (Im using a resistive load of 12ohm )

Plz can help me solve this issue ASAP

Thanks for replying

But the situation is still same there is still startup issues , if we compare o/p of various pins of ic to datasheet its night & day 

I tried another optocoupler but result is same  design link 

is the IC model faulty ? or some other issue ?

Hi Shreyes,

I'm not sure what the issue is, let me confirm with my team. Please allow until early next week for an update here. 

I cannot see a label for Vin as you have for Vout and Iout, but it still shows up on your plots ...

Try isolating the primary and secondary reference/ground connection. 

In the mean time, what values are you entering for start and end display of the transient analysis? Are you changing any of the other transient simulation parameters? 

It may be worth testing a physical version of this circuit to confirm there is not issue with the model, especially considering the output is 12V and 1A like you want.

Regards,

Andrew

1588.LM5021_close.TSC

For transient im using 0-100m (operating point)

Although im getting o/p for 12V1A but when i try to get 12V2A im not getting proper o/p thats why i want help with startup issues of IC 

Can you get back with a sol. by monday ?

Regards,

Shreyes 

Hello Shreyes,

Yes, I can share more suggestions to try and solve your issue by end of Monday.

Regards,

Andrew

Hi Shreyes,

I've tried making further edits to your existing TINA schematic file and I'm still not seeing the results I expect.

To verify there is nothing wrong with the model and to isolate any issues with the macros you're usaing, I loaded the TINA reference design from the product page (LM5021-1 TINA-TI Transient Reference Design), and ran a transient simulation (zero initial values) with an end time of 5m, this worked perfectly.

I recommend you copy the values of all components (transformer, RCs, etc) from Webench results (LM5021_close) into the provided transient reference design (snvm454_edits) and resimulate using the parameters provided (5m timeframe). 

snvm454_edits.TSC 

8054.LM5021_close.TSC

Regards,

Andrew

I have tried this before yet it didn't improve result, there are 2 ICs 80% & 50% duty cycle , tried both still not getting o/p

Hi Shreyes,

Thanks for trying, can you share the edited file you created so that I can suggest more edits? 

Were you not able to get the peak 2 A output current like you previously tested?

Regards,

Andrew