LM25085A

Giampaolo Braga

Other Parts Discussed in Thread: LM25085A, LM25085

Hi. From Italy. I built this power supply with 30V input 12V output 3.5A output based on Webench software. (see diagram below). The result is that I have 17V at the output instead of 12V, both with no load and with a 4 ohm load. Why? the values of the RFB1 and RFB2 resistors are exact. Help thanks

over 3 years ago

0 Orlando Murray over 3 years ago

TI__Mastermind 22299 points

Giampaolo,

Section 8.2.2 of the datasheet show the feedback resistor equation RFB2/RFB1 = (VOUT/1.25V) -1

You can increase the lower feedback resistor from 806 to 1.15kΩ to get a 12V output.

Sorry about that, maybe the WEBENCH VREF value is incorrect (0.9V instead of 1.25V)

-Orlando

0 Giampaolo Braga over 3 years ago in reply to Orlando Murray

Prodigy 30 points

oooooooooooooooh my mistake !!!
I was convinced that I mounted LM25085A, instead I had mounted LM25085 (without the A) and now I have redone the calculation and now with R 1.15K everything is ok, 12V output
thank you very much Orlando

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LM25085A