LM3478

HI Ian,

Where exactly are you seeing this warning? Can you send the screenshot?

Thanks,

Hi Nikhil,

The warning actually came up in a box when i ran a simulation the first time, now I can't seem to repeat it ( I haven't used the program too much ). However I still get the message if I look in the eSIM report I still get the warning. Hopefully I've uploaded the report correctly...

Best regards

8867.webench_LM3478_warmup_start.pdf

Hi Ian,

I will look into this and get back to you.

Thanks,

Hi Ian,

First off, thanks for pointing out the language mistake, I'll get that fixed promptly.

Now the turn ON problem:
Even though your minimum input is supposed to be 11V the LM3478's internal UVLO is about 2.85V, and the part has 100% Dutycycle capability. What we have seen is that on startup, when your source is going from 0V to 11V if its slow , the LM3478 starts trying to work at 2.85V, this allows it to pull a large current from your source at 100% dutycycle. Depending on the source's sourcing ability, this can cause a sort of current limiting cycle where your source doesn't ever properly start up.

To get around this if you see it, or to preempt it, a simple RC filter can be placed at the Vin pin. This causes a lag in the startup of the LM3478 so that your source has the proper time to startup.

I hope this helped clarify the issue. Let me know if you have more questions.

Hi Tommy,

Thanks for your reply.. Just to be sure..  If I understand correctly, a warning is being given that the 'driving' source may encounter 'issues' trying to provide sufficient startup current. So, putting a filter into the 3478's supply slows its startup allowing the driving source a 'safe zone' to get going. Does that sound right ?By the way, is this the same as the 'soft start' function in other parts ?

Best Regards