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LP8556: VBOOST setting

Mark Guastaferro
Genius 11645 points
Part Number: LP8556

When configuring the VBOOST value in adaptive boost mode, does this value include any headroom? For example, if I set the VBOOST for 30V, does this represent the initial voltage across the LEDs, such that the actual boost voltage relative to GND will be 30V + LED headroom?  

Also, why are there two registers to set the LED headroom setting:  DRIVER_HEADROOM and HEADROOM_OFFSET? It's clear that the threshold is based on the sum of these settings, but does it matter which settings are used to achieve a particular value?

  • 0
    TI__Expert 4565 points

    VBOOST is initial boost voltage means actual voltage output doesn't include headroom voltage.

    Once boost ramps up, boost voltage reaches up to 30V until LED driver turns on, then boost voltage is adapted to LED voltage+headroom voltage.

    For headroom control options, both register options will contribute final low comparator value, and either one can be used to adjust headroom voltage. Originally, DRIVER_HEADROOM was added to give more flexibility of headroom control as I remember, but it' doesn't need to be used actually.

    Every EPROM version of LP8556 only use HEADROOM_OFFSET control with min setting of DRIVER_HEADROOM.

    Hope this helps,