IC specification
MLX10803
High power LED driver
3901010803 Page 21/25
Data Sheet
Rev026 Jun/2012
8. Temperature regulation
In normal mode the peak current threshold voltage is defined by the lowest voltage on pins VREF, IREF2 and
IREF1. Usually the resistor connected to IREF2 pin has a small thermal coefficient and the resistor on IREF1 pin
has a big negative temperature coefficient (but they also can be connected vice versa). Both of these pins have an
output current of 50 µA. When the voltage on pin IREF1 falls below the voltage on pin IREF2 or VREF, the voltage
reference for the actual maximum current is taken from pin IREF1. This makes the value of the peak current
sensitive to temperature and prevents overheating of LED or IC. When the voltage on pin IREF1 becomes higher
than voltage on IREF2 or VREF, the reference switches back to IREF2 or VREF pin.
The thermal behaviour of the system should be characterised during the design-in of the product by the user.
For a system that is designed for thermal conditions, temperature down regulation may not be needed. In this case,
It is enough to leave the IREF1 or IREF2 pin unconnected and the internal current source will pull it up to the
voltage Vdd – 0.7V.
System behaviour can be configured to compensate the dependency of LED light output versus temperature. The
example of such compensation is depicted below.
Illustration of a possible temperature regulation
Constant light
Saved energy
40% of the light at 25°C
0
50
100
150
200
250
300
350
400
450
500
0 20 40 60 80 100 120-20
Junction Temperature, T
J
(°C)
20
40
80
100
Light output from Amber LED with constant current supply
Compensation current funtion
Thermal protection function
Resulting thermal compensated and protected light output from an Amber LED
60
