LM70840-Q1: LM70840-Q1 - design calculations

Roger Fernandes

Prodigy 20 points

Part Number: LM70840-Q1
Other Parts Discussed in Thread: LM70840, LM70880

Tool/software:

I need to design a buck converter with below specifications:

Input voltage: 17V to 63V.

Output voltage: 12V.

Load current: 1.5A max.1.2A Typical.

Ambient temperature max.: 85 deg C.

Output capacitor: Electrolytic + Ceramic.

Inductor: Shielded.

Please provide the peripheral component values with calculations.

5 months ago

0 Ben C 5 months ago

TI__Guru 56345 points

Hi Roger,

Please use the quickstart calculator to help with your design.

https://www.ti.com/tool/download/LM70XX0-CALC

Ben

0 Ben C 5 months ago in reply to Ben C

TI__Guru 56345 points

Hi Roger,

Are there any updates?

Ben

0 Roger Fernandes 5 months ago in reply to Ben C

Prodigy 20 points

Hello Ben,

What is the difference between LM70840 and LM70880 ICs?

When calculating derating, the thermal metric is the same. Ambient is 85deg C. So how can I say that higher current will flow?

0 Ben C 5 months ago in reply to Roger Fernandes

TI__Guru 56345 points

Hi Roger,

I think the FETs are sized proportionally to the rated current of the variant.

Ben

0 Roger Fernandes 5 months ago in reply to Ben C

Prodigy 20 points

...also, if I use datasheet formulae to calculate peripheral component values, I get different from the Webench designed values. How do I justify this in design notes?

0 Ben C 5 months ago in reply to Roger Fernandes

TI__Guru 56345 points

Hi Roger,

Can you provide an example? The fastest way to calculate the BOM values is to use the quickstart calculator.

Ben

+1 Ben C 5 months ago in reply to Ben C

TI__Guru 56345 points

Hi Roger,

If there are no further questions, please close the thread by clicking on "resolved". Thank you,

Ben

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LM70840-Q1: LM70840-Q1 - design calculations