mlx10803 Melexis Company, mlx10803 Datasheet - Page 17

• Manufacturer Part Number: mlx10803
• Description: Ic Specification Mlx10803 High Power Led Driver
• Manufacturer: Melexis Company

After powering on the MLX10803 the switch becomes open and the current through the LED starts to rise. The rate
of current raise is limited by the value of the coil. When the current through the LED reaches half of a maximum
value, the ON timer is started, and if during 58.5 clocks of the internal oscillator the maximum current value through
the LED is not reached, the driver switches off. This maximum current is adjusted by the resistors on the IREF2,
IREF1 or voltage applied to VREF pins (voltage on these pins is divided by 5). The minimum of these voltages is
taken as a reference. The driver is switched off for a monoflop time, which is equal to 9…16 pulses of oscillator.
The frequency of the oscillator can be set by the customer using the Rosc value using such formula:
Both parameters, the peak current threshold voltage and the monoflop time, create an ON/OFF period to form an
average current through the LED. By adjusting these parameters, an adjustment of the average load current is
possible in a wide range.
Note: The current sense comparator has a typical debouncing time of 300ns as shown in the block diagram. This
delay time prevents the driver from being switched off due to short term switching oscillations. When working with
very short monoflop times, this time has to be taken into account for calculations.
By applying a PWM signal on VS/PWM, the LED can be dimmed from 0% to 100%.
VS/PWM = L
VS/PWM = PWM
VS/PWM = H
Fosc
Imax
3901010803
Rev 025
Imax1
Iavg
Imax2
Iavg2
Iavg1
Iavg1
Iavg2
Imax
I
I
I
[
MHz
7.2.
T1
]
T2
222
The principle in detail
2 .
/(
Rosc
LED permanent OFF
LED dimmed with PWM between 0% to 100%
LED permanent ON
tmon_off
[
k
]
. 4
44
)
.
Page 17/25
IC specification
t
t
t
High power LED driver
MLX10803
2/OCT/07
Data Sheet