IC specification

MLX10803

High power LED driver

3901010803

Page 5/25

Data Sheet

Rev026

Jun/2012

1.1.2. Principle soft start up LED driver diagram

ROSC

IREF2

VREF

GND

RSENSE

DRVGATE

VS/PWM

VBAT

GND

100nF

Cap for EMC directly

on the connector

100nF...1uF

IREF1

Figure 1:

1.1.3. LED driver application notes

The MLX10803 is optimised for the use of low cost coils and n-channel MOSFETs. For a standard application with

1 LED and an average current of 350mA, a coil of about 100µH…220µH and ≤ 1Ω DC resistance should be

chosen. The sense resistor should have a value between 0.27Ω…0.47Ω / 250mW.

As a general rule: for higher load current lower inductance of the coil is needed because higher currents lengthen

the charging time of the coil. Thus, switching frequencies may become lower than 20kHz which is often not desired.

It is possible to set the peak current and the average current of the LED by variation of the RSENSE resistor, the

coil value and the internal oscillator frequency (ROCS resistor).

The flyback diode that carries the load current during the passive state (driver OFF) should be a fast switching and

low intrinsic capacitance diode like ES1D or BYG80 in order to avoid parasitic spikes on RSENSE. The diode must

be able to carry the LED current flowing during the OFF time of the driver.

The n-channel MOSFET should have low intrinsic capacitances, a drain-source voltage suitable for the application

and must be able to carry the current flowing through the LED(s) during the ON time. To decrease the time of

transistor switching and to improve the thermal behaviour of the module, the lines between transistor and IC should

be minimised.

For applications that use an NTC resistor for temperature sensing, the NTC value has to be selected according to

the application requirements. For most applications, a NTC value up to 470kΩ will be suitable.

In case of longer lines between the IC and the coil (which should be avoided because of EMI), a capacitor might be

placed in parallel to RSENSE to avoid crosstalk and parasitic switching. Well chosen parameters for external

components can help to avoid such conditions. The goal should be to unload the coil as much as possible during

the selected off time (see also chapter 7).