lm5122 : Problem on the SOFT-START Css capacitor evaluation

penef yorgen

Other Parts Discussed in Thread: LM5122

hi all
I want to use the lm5122 to convert 12V to 5 V (with high output current 5A to 10 A).
I chose the lm5122 because in the near future this output voltage will be greater ( 48V max).
But my problem today is the SOFT-START which is programed by the Css capacitor. In the data sheet the equation 11 give me a negative time (because my input voltage is bigger than my output voltage) ????
Some one can give me some informations concerning this observation?
how can i estimate tss?
For the end, if the lm5122 can realise my specifications??
Thank all
Penef

over 12 years ago

0 EricLee over 12 years ago

TI__Guru 60061 points

LM5122 is a controller for boost topology . Boost converter converts the lower input voltage to the higher output voltage.

If the input voltage is higher than target output voltage, no soft-start time is required since your output voltage is higher than the target output voltage before starting.

LM5122 cannot be used to conveter 12V to 5V.

Regards,

Eric

0 penef yorgen over 12 years ago in reply to EricLee

Prodigy 20 points

Hi Eric
thank you for your answer
Penef

Power management

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lm5122 : Problem on the SOFT-START Css capacitor evaluation