LM3405A: ILED of Recommended Operating Conditions

Shinichi Inoue

Guru 19961 points

Part Number: LM3405A

Dear Specialists,

My customer has a question about Recommended Operating Conditions of LM3405A datasheet and LM3405A Demo Board.

I would be grateful if you could advise.

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The LED current is described as IF on the data sheet, but only the Recommeded Operating Conditions has an item as ILED.
Is this ILED the same as the LED current(IF)?

If so, In case of the SOT package is 400mA.
We'd like to use IF = 700mA, is it impossible due to this restrictions.

What conditions are LED current restrictions set?
Please tell me about the calculation method.

On the other hand, the LM3405A demo board using the SOT package had a default R1 = 0.2Ω and IF = 1A setting.

Why can it be used with 1A output.

https://www.tij.co.jp/jp/lit/pdf/snva271

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I appreciate your great help in advance.

Best regards,

Shinichi

over 2 years ago

+1 Yuting Shao over 2 years ago

TI__Genius 13001 points

Hi,

You can set any output current through this formula: 205mV / R1 only if this current plus half ripple is below current limit 2A.

Robin

0 Shinichi Inoue over 2 years ago

Guru 19961 points

Hi Yuting,

Thank you for your reply.

You mentioned for setting the LED current.

In this case, it is determined by current limit(2Atyp) and R1.

I can understand at this point.

Could you please explain why are there the recommended operational value(SOT:400mA and MSOP-PowerPAD:1A) .

The customer is concerned that they may not be able to use more than these current values.

I appreciate your great help and cooperation.

Best regards,

Shinichi

+1 Yuting Shao over 2 years ago in reply to Shinichi Inoue

TI__Genius 13001 points

Hi Shinichi,

That's a recommended operating condition considering of thermal situation. Larger output current will bring device temp rising. If this is allowed from customer side, larger current should be OK.

Robin

0 Shinichi Inoue over 2 years ago

Guru 19961 points

Hi Yuting,

Thank you for your reply.

I understand Recommended Operating Condition is only as a guide.

It is able to use larger current as long as it does not exceed Tjmax.

Also, do ILED and IF have the same meaning in the datasheet？

I appreciate your great help and cooperation.

Best regards,

Shinichi

+1 Yuting Shao over 2 years ago in reply to Shinichi Inoue

TI__Genius 13001 points

Hi Shinichi,

Yes, ILED and If share the same meaning in the datasheet.

Robin

0 Shinichi Inoue over 2 years ago

Guru 19961 points

Hi Yuting,

Thank you for your reply.

The customer understand your suggestion.

They consider MSOP-PowerPad package.

I appreciate your great help and cooperation.

Best regards,

Shinichi

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LM3405A: ILED of Recommended Operating Conditions