LM3478: LM3478 design used Webench

Eric Shen42

Part Number: LM3478

Dear TI:

When I used Webench to design LM3478 schematice, the Webench hint: "With the design conditions, either the IC or the selected FET junction temperature is exceeded above the maximum rating. Hence, this design is created using an ideal FET. Please note that the resulting FET parameters are ideal, so the efficiency/loss opvals have been disabled. Also, the schematic/PCB export and Thermal simulations will not work with the ideal FET."

What does that mean?Does it mean that LM3478 cannot actually meet the design requirements?If it can be satisfied, can you provide a reasonable design device selection?

Thanks!

The design requirement is:
Vin=3.2V-4.2V

Vout= 50V/0.2A

over 6 years ago

0 Jasper Li over 6 years ago

TI__Mastermind 46905 points

Hi Eric,
the engineers supporting this device is out of office as the holiday. they can reply you after back to office late this week or next.
from my opinion, the VOUT/VIN ratio is high in this application. we should use flyback toplogy, otherwise the duy cycle could be too large and efficiency is not good.

0 Garrett Roecker over 6 years ago

TI__Mastermind 21720 points

Hi Eric,

This usually just indicates that there is not a suitable FET in the library. Based on the design parameters it should be possible to find a MOSFET that meets this requirement.

Are you trying to implement a flyback regulator or a boost regulator? This will help with the MOSFET selection.

Thanks,

Garrett

0 Eric Shen42 over 6 years ago in reply to Garrett Roecker

Expert 2750 points

Hi Garrett:
Thanks!

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LM3478: LM3478 design used Webench