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LP8865Y-Q1: LED driver

Farhad Pirvali
Prodigy 120 points
Part Number: LP8865Y-Q1

Hi Team,

I have a question about the device LP8865Y, or LP8865V.
In the datasheet it is mentioned that the input voltage range is between 4.5 to 65 volts, but the output voltage range is not clear, it is also not clear what would be the maximum number of LEDs in series, and which forward voltage for LED?
Could please make it clear for me?
Can I use 22 LEDs in series? That would be maximum output voltage 82.5V

Do you have such a device that can drive 22 LEDs with Maximum voltage 82.5volt in 350mA as constant current?

  • 0
    TI__Mastermind 19810 points

    Hi, Farhad

    It is hard to do so.

    Our device can afford 65V for each pin, 

    So for buck boost topology, VIN + VLED should lower than 65V.

    By the way, for maximum output voltage 82.5, why you want a buck-boost topology?

  • 0 in reply to Zhiqian Wu
    Prodigy 120 points

    Hi Zhiqian,

    Thanks for your comment.

    In the original requirement, I have to design a constant current LED driver to handle two variants of LED PCBs.
    The LED PCBs can be 11 LEDs in series or 22 LEDs in series.
    The nominal forward voltage for LEDs is 2.7v, but the min, and max voltage range of the LEDs to cover two variants is between 19V to 82.5V
    The min/max forward voltage of LEDs is 1.75v/3.75v

    the specification is like this:

    1. Input voltage (12V to 48V) AC or DC
    2. Two group of LEDs:
    2.1. Gr1: 11 LEDs (Nominal voltage: 11 x 2.7v = 30V)
    2.2. Gr1: 22 LEDs (Nominal voltage: 11 x 2.7v = 60V)
    so the voltage output range would be 19v to 82.5v

    3. the nominal LED current is 350mA

    4. The Power Factor should be more than 0.85
    5. The efficiency of the system should be more than 85% (for nominal input voltage 24v)
    6. The THD must be less than 20%

  • 0 in reply to Farhad Pirvali
    TI__Mastermind 19810 points

    Hi, Farhad

    It is hard to cover the all range of input in buck-boost mode.

  • 0 in reply to Zhiqian Wu
    Prodigy 120 points

    Ok, then the idea is using an Active bridge rectifier and PFC BOOST to rise up the input voltage to a proper level then use the Buck converter or DC/DC LED driver, But I do not know what would be the best option for PFC and DC/DC LED driver?
    By PFC Boost we can rise the voltage up to 100 volt then use a DC/DC converter or LED driver

  • 0 in reply to Farhad Pirvali
    TI__Mastermind 19810 points

    Hi, Farhad

    If you could rise up the voltage for example, 50V. and you can use LP8865Z to reduce the voltage in into 11LED I think.

  • 0 in reply to Zhiqian Wu
    Prodigy 120 points

    Hi Zhiqian,

    In this family (LP8865) those parts (with suffix V or Y) act as Buck-Boost, so I think it should work, while input voltage is 50V and only 11 LEDs used then it acts as buck converter and when 22 LEDs connect it should act as boost converter, isn't it?

  • 0 in reply to Farhad Pirvali
    TI__Mastermind 19810 points

    Hi, Farhad

    LP8865Y is a buck -boost version.

    LP8865Z is a buck version.

    LP8865Y is hard to cover 11LED and 22LED in this case. Because LP8865Y needs the condition that Vin+VLED is lower than 65V.

  • 0 in reply to Zhiqian Wu
    Prodigy 120 points

    Hi Zhiqian,

    Ok thanks, clear, I thought because it is buck-boost, the output voltage can go higher than input while input is for instance 50V.