LM3402 Vo vs Total Vf

Khaled Chowdhury

Other Parts Discussed in Thread: LM3402

Hi,

I'm using the LM3402 to drive 10 ThorLabs near-infrared LED's in a series at 100mA, but had a question about the Vo of the device. Forgive my ignorance, but will there be any issues if the forward voltage of each LED changes? Because of incomplete data from the datasheet, I cannot really tell what exactly my Vf will be for the LED at 100mA, as it says it only says it is 1.2V @ 20mA and 1.5V max.

As you know, the Vo is crucial in deciding what inductors to use, so I'm in a bit of a pickle. I'm aware of the excellent WEBENCH tool, and would like to use it once I'm cleared of this confusion.

P.S.: I'm running it off of a 24V power source, and will be using it enabling it using the Low Power Shutdown Mode by controlling the Ron pin.

Any insight will be helpful!

Cheers,

Khaled

over 9 years ago

0 David Zhang over 9 years ago

TI__Expert 3495 points

Khaled:
LM3402 is a constant current LED driver. Vout change does not affect the LED current. The current is well regulated. Vout change does change the switching frequency but it is not going to be a problem in the operation. You can select inductor based on the lowest Vout value. Don't worry about Vout change.
David Zhang

0 Khaled Chowdhury over 9 years ago in reply to David Zhang

Prodigy 20 points

Thanks David!

I'll put the lowest value onto WEBENCH and get my design then.

Cheers.

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LM3402 Vo vs Total Vf