MLX10803_06 Datasheet, PDF (18/25 Pages) List of Unclassifed Manufacturers – High power LED driver

IC specification MLX10803
High power LED driver
Dimming is achieved by applying a PWM directly to the module supply or by changing the reference voltage on pin
VREF or the resistor’s value on IREF2 pin.
IC settling times must always be considered in PWM mode. Please refer also to chapter 1.1.4 for
additional PWM frequency considerations.
Limitation of the ON time prevents from exceeding the allowed average current when the power supply voltage is
not sufficient for the current to reach its peak value and restricts in this case duty cycle of switching to 68%.
I
Imax
Iavg
Imax/2
tmon_on
tmon_off
t
A pseudo random generator is applied to the monoflop time. The pseudo random generator runs with the clock
derived out of the monoflop time and adds a random distribution on these 3 LSBs. Therefore, the monoflop time
gets a random variation from its value. The EMI behaviour of the complete module is improved due to the variation
of the otherwise fixed switching frequency.
The inductance L of a coil describes the amount of magnetic energy that can be stored in it.
Consequently, high inductive coils will be discharged less than low inductive coils in a given time.
Generally the coil can be driven in two different ways:
1)
The coil is discharged partially only. That means the coil still carries a significant amount of energy
when going from discharging to charging. In that moment the charging current rises immediately to
the coil current that was flowing just before switching. This is connected with large dI/dt transients on the
RSENSE pin that have a negative impact on EMI. This is mostly preferred way of regulation because of low
influence of supply voltage and coil value on output current. Fast flyback diode is recommended and extra
important in this case.
2)
The coil discharged completely. Thus, at the end of a discharging cycle, the coil doesn’t carry energy
anymore. With the next charging cycle, current increases steadily from around zero. This way, large dI/dt
transients are completely avoided.
3901010803
Rev 024
Page 18/25
Data Sheet
7/DEC/06