LP3954 Datasheet, PDF (24/60 Pages) National Semiconductor (TI) – Advanced Lighting Management Unit

LP3954
SNVS340D – JUNE 2005 – REVISED MARCH 2013
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Figure 20. Output Current vs Pin Voltage (Current Figure 21. Pin Voltage vs Output Current (Switch
Sink Mode)
Mode)
Figure 22. Output Current vs R_RGB (Current Sink Mode)
Single High Current Driver
LP3954 has internal constant current driver that is capable for driving high current mainly targeted for FLASH
LED in camera phone applications.
MAXIMUM CURRENT SETUP FOR FLASH
The user sets the maximum current of FLASH with R_FLASH resistor based on following equation:
I_MAX = 300 × 1.23V / (R_FLASH + 50Ω),
(3)
where
Imax = maximum flash current in Amps (ie. 0.3A)
1.23V = reference voltage
300 = internal current mirror multiplier
R_FLASH = Resistor value in Ohms
50Ω = Internal resistor in the I_FLASH input
For example if 300mA is required for maximum flash current R_FLASH equals to
R_FLASH = 300 × 1.23V / I_MAX – 50Ω = 369V / 0.3A – 50Ω = 1.18kΩ
(4)
24
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