EVB10803 Melexis Company, EVB10803 Datasheet - Page 4

• Manufacturer Part Number: EVB10803
• Description: Evaluation Board Evb10803 Power Led Driver For Automotive Applications
• Manufacturer: Melexis Company

In PWM mode, the jumper JMP1 must be removed to open the connection to VBAT!
Please note that there is no polarity protection in the PWM line! The user has to ensure the
correct polarity of the PWM signal!
The VREF input is intended to be used to set an optional voltage reference for the RSENSE peak current threshold
level. It acts in the same way as IREF1 and IREF2 inputs but has no internal pull up current sources. Thus, the
voltage at VREF must be applied from extern. If the voltage level at VREF becomes lower then the voltages on
IREF1 and IREF2, this voltage becomes dominant and is used (divided by 5) as the RSENSE current threshold
level. With that feature, it is possible to have a 2
tail/break lights.
Whether this pin is an analogue input, it can also be used as an alternative, digital PWM input. The user has to
ensure that the voltage level during the ON state is higher then the dominant level on pins IREF1/IREF2. As the
highest possible voltage on both IREF pins can be 3.8V, a PWM signal with a signal amplitude of 5V (standard
logic or µC output) is best suited.
Furthermore, the OFF time signal amplitude has to be < 20mV, as any higher level on that pin is interpreted as
voltage input level and used for setting the RSENSE current threshold level.
As default, the VREF pin is externally pulled up to VS by a 470k resistor. This way, the VREF pin is always
recessive (“H”) in case it is not used.
In order to avoid destruction of the LED(s) due to overheating, the MLX10803 offers the possibility for a
temperature down regulation. Via connector J3, a NTC resistor can be connected as a temperature sensor. For
best results, the NTC should be thermally connected to the LED(s).
The NTC is connected to the IREF2 Pin of the MLX10803. For a quick adaptation to a certain application, the PCB
consists of two unpopulated 0805 pads for a serial and a parallel resistor (R6, R7). With these resistors, the
regulation starting point can be manipulated as desired. As default, the pad for the series resistor (R7) is shortcut
by a thin PCB trace. If a series resistor should be used, this trace has to be cut off before it is populated.
If temperature down regulation should be used, the parameters monoflop time (by potentiometer R4, ROSC) and
LED peak current (by potentiometer R5, IREF2) have to be adjusted first.
The voltage on pin IREF2 is measured and taken as a reference to define the starting point for the temperature
down regulation.
The voltage on pin IREF1, that is defined by the resistance of the NTC (together with the optionally used R6/R7),
must have the same voltage level as IREF2 at the corner temperature, where the down regulation starts to work.
So, the overall resistance of IREF1 is similar to the resistance on pin IREF2 at that corner temperature.
For a better illustration, an example is given below:
T
R
390121080301
20/Mar/2006
Author: SSZ
Start
IREF
2
8.3.
8.4.
85
47
C
k
Using the VREF input as a second peak current threshold level
Using an external NTC as temperature sensor
Rev. 5.01
Evaluation board EVB10803
Power LED driver for automotive applications
nd
LED current/light output as it is used for example in combined
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