MLX10803_06 Datasheet, PDF (19/25 Pages) List of Unclassifed Manufacturers – High power LED driver

IC specification MLX10803
High power LED driver
Because of randomisation, the discharging time is not constant but varies within a certain range. It must be
ensured that only the longest possible monoflop time completely discharges the coil. Otherwise the coil is
discharged before the monoflop time ends which results in a loss of accuracy.
I
Imax2
Resistance 2
Imax1
Iavg
Resistance 1
Coil 1
Coil 2
Toff
Coil 1 > Coil 2
Resistance 1 > Resistance 2
t
Conclusion:
In most cases the coil is driven in a combination of both ways. A trade off has to be made between
EMI behaviour and maximum allowed LED current. By varying these parameters, an optimum can
be found for every application.
Below are some examples for typical parameter sets given for a 4A LED current and the following application data:
• RSENSE = 0.1 Ω/ 2 watt
• ROSC = 270kΩ
• L = 47µH, 4A minimum, 0.05 Ω
• Normal nFET switch transistor, rds on < 0,01 Ω
Remarks:
• 4A and 0.05 Ω results in 0.8 watt power dissipation over the coil.
• 4A and 0.1 Ω for the RSENSE resistor results in 1.6 watt, but only for 50% of the time in average.
• The LED(s) with this current will dissipate 32 watt if they have 8V forward voltage.
3901010803
Rev 024
Page 19/25
Data Sheet
7/DEC/06