MLX10803 datasheet(21/25 Pages) ETC2

21 / 25 page

IC specification

MLX10803

High power LED driver

3901010803

Page 21/25

Data Sheet

Rev 025

2/OCT/07

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

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