LM5118: Designing the Input filter of LM5118

Kiran S

Part Number: LM5118-Q1
Other Parts Discussed in Thread: LM5118

Hi,

I need to design the input filter for the LM5118, I was referring to the app. note snva538. Under the Appendix example calculations, DC resistance Rl = 0.088 ohm, How did they get the value and How do I find the Rl for my circuit where active IC's are connected to the converter.

Attaching the webench design link below -

webench.ti.com/.../SDP.cgi

Regards,

Kiran

over 1 year ago

0 Brigitte over 1 year ago

TI__Guru 60235 points

Hello Kiran,

DC resistance in SNVA538 is the resistance of the inductor. The inductor datasheet should this include.

Best regards,
Brigitte

0 Kiran S over 1 year ago in reply to Brigitte

Prodigy 50 points

Hi,

Thank you for clearing my confusion (nd sorry for that stupid question) and i have one more doubt, in the example schematic input capacitance value is 82uF but in the 14th page of the app. note the input capacitance of the power supply is given as 15uF, is this typo ?

0 Brigitte over 1 year ago in reply to Kiran S

TI__Guru 60235 points

Hello Kiran,

I expect you are right, but here I am not as sure as for the above parameters. You might find the answer to this questions in the MathCad files mentioned in this thread: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/266346/broken-mathcad-link---nation-input-filter-design-for-switchers-whitepaper?keyMatch=NATIONAL+INPUT+FILTER+DESIGN+FOR+SWITCHERS+ZIP

Another possibility to design the input filter would be to use the power stage designer: POWERSTAGE-DESIGNER Design tool | TI.com

There you can find as well a filter designer.

Best regards,
Brigitte

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LM5118: Designing the Input filter of LM5118