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TPS92661 LED control method and LM3409 Rsns

JeffYC Yang
Expert 1290 points
Other Parts Discussed in Thread: LM3409, LM3409HV

Hi Sir,

I have below question need your help.

If I used LM3409 + TPS92661 to driving 12 pcs LED, if LED Vf= 12V, LM3409 input most need provide 12 x 12V = 144V or higher to driving 12 pcs LED? or TPS92661 can control 12pcs LED each one by parallel? 

Thanks!

Jeff

  • 0
    TI__Prodigy 710 points
    Hello Jeff,

    Unfortunately, this partition will not work.

    1. For a 12V LED (assuming it is only a two-terminal device), the Vf of that LED will always trip the TPS92661 "LED OPEN threshold voltage". This means that every time the TPS92661 tries to open the switch, it will be immediately closed to prevent damage to the FET.

    2. The LM3409HV has a max VIN of 75V. So, 144V is not possible.

    3. The TPS92661 does not allow for paralleled control of the LEDs. TPS92661 is designed for individual LED control in a series string of LEDs.

    I hope this helps.

    Best Regards,
    Mike
  • 0 in reply to M. Drake
    Expert 1290 points

    Hi Mike,

    I meet a LM3409+TPS92661 issue now.

    I just clarify LED Vf with customer, Vf = 3V, and schematic as below, Could you please help us to review below schematic,

    We already move R20 to current path, and change value to 1.65ohm, but seems still not work.

    Even TPS92661 not work, defult register let all 12 pcs LED turn on? or it default off, bypass by internal MOSFET, need setup register to turn on?

    If need setup register first? What address and value need write to register?

    , KW H4L531.TE - Oslon Black Flat.pdf

    Thanks!

    Jeff