LM3509: One 6x LED string vs. 2 3x LED strings

Austin Allen

Part Number: LM3509

Hello all,

My customer is looking to illuminate 6x LEDs using <50mA of ILED. I saw in another thread that it was recommended to split into two unison rails between MAIN and SUB/FB with 3x LEDs on each rail rather than put 6x LEDs on MAIN and leave SUB/FB floating. Any particular reason for this? Or is the 6x LEDs on one string okay?

Thank you,

Austin

over 1 year ago

0 Patrick Yao over 1 year ago

TI__Mastermind 19610 points

Hi Austin,

It's recommended not to put more than 5 LEDs in one series. If SUB/FB is not used to drive LED, it should be used to regulate the output voltage through a resistive devider.

Patrick

0 Austin Allen over 1 year ago in reply to Patrick Yao

TI__Intellectual 1550 points

Hi Patrick,

Could you elaborate just a bit? How come it isn't recommended to put more than 5 LEDs in one series? Would I really want to regulate the output voltage if I'm not using an OLED screen?

Best,

Austin Allen

0 Patrick Yao over 1 year ago in reply to Austin Allen

TI__Mastermind 19610 points

Hi Austin,

Since I haven't done bench test on this device so my previous explanation was only based on datasheet.

I think you are right, it seems output voltage only needs to be regulated with OLED panel.

So could you please send me more info about your testing requirements? I'll do some test on EVM first and will give you feedback then.

Patrick

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LM3509: One 6x LED string vs. 2 3x LED strings