SNVAA19 May   2021 LP8863-Q1 , LP8864-Q1 , LP8864S-Q1 , LP8866-Q1 , LP8866S-Q1

 

  1.   Trademarks
  2. 1Introduction
  3. 2Boost Output Voltage Range Design Consideration
  4. 3Boost UVP Design Consideration
  5. 4Boost OVP Design Consideration
  6. 5Calculation of Feedback Resistor Values
  7. 6Feedback Resistor Calculation Example
  8. 7References

2 Boost Output Voltage Range Design Consideration

Feedback resistors are selected to ensure that the minimum boost voltage with ISEL = 0 μA is below the minimum LED string voltage, as shown in Equation 4. The maximum boost voltage with ISEL = 38.7 μA need to be at least 2 V greater than the maximum LED string voltage + the maximum headroom at LED sink pins as shown in Equation 2.

Equation 1. GUID-20210423-CA0I-8F7V-XGLK-NGMK8MPMPJZM-low.gif
Equation 2. GUID-20210423-CA0I-R2MS-BQVC-TND7Z6JVDPWD-low.gif

Where:

    • VMINBOOST is the minimum boost voltage when ISEL = 0 μA (minimum)
    • VMAXBOOST is the maximum boost voltage when ISEL = 38.7 μA (maximum)
    • VSTRING is the voltage across LED string
    • VHEADROOM is the headroom voltage of LED current sink and can be substituted with 1 V in Equation 2
    • 2 V in Equation 2 is an empirical design margin considering the variations of internal reference and the tolerance of feedback resistors.