2 Boost Output Voltage Range Design Consideration

Feedback resistors are selected to ensure that the minimum boost voltage with I_SEL = 0 μA is below the minimum LED string voltage, as shown in Equation 4. The maximum boost voltage with I_SEL = 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.

Equation 2.

Where:

• • V_MINBOOST is the minimum boost voltage when I_SEL = 0 μA (minimum)
  • V_MAXBOOST is the maximum boost voltage when I_SEL = 38.7 μA (maximum)
  • V_STRING is the voltage across LED string
  • V_HEADROOM 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.