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LP8861-Q1: maximum supportable LED Vf

Masatoshi Oguri
Expert 4780 points
Part Number: LP8861-Q1


Hello,

One of my customer is considering using LP8861-Q1 for LED string of total Vf around 40V.

However, it looks there is no criteria to determine how high voltage the device can support.

Would you show me some guideline?

The detasheet recommends Vmax at 30% higher than maximum Vf; however, the design example seems applying merely 23% higher than typical Vf.

This is inconsistent and cannot be a guideline.

Thank you.

Regards,

Oguri (TIJ automotive FAE)

  • 0
    TI__Expert 4565 points

    Hi Oguri-san,

    I guess you're mentioning about an example for SEPIC case.

    Generally speaking, voltage margin of boost over LED Vf can be various depending on LED quality and characteristics.

    If LED Vf changes easily across production bins and temperature, you will need to have more margins, and the other way around for opposite cases.

    I believe that 30% came from worst case scenario considering these kind of variables.

    For SEPIC case example, only 4 LEDs were used per string. In this case, some of Vf variation of each LED will be much less than higher number of LEDs per string. So less margin can be still OK. But you can still design boost out voltage targeting 30% margin all the time.

    Hope this helps,