IC specification

MLX10801

Power LED driver for automotive applications

Power saving low side coil driver

Electronic fuse

3901010801

Page 6/41

Rev 021

14/July/05

Author: TFR

revised: RAH/SSZ

1.1.3. LED driver application notes

The MLX10801 is optimised for the use of low cost coils. For a standard application with 1 LED and an average

current of 350mA a coil of about 100µH…470µH having ≤ 1R omic resistance should be chosen. The sense resistor

should have a value between 0.47R…1R / 250mW.

As a general rule: the higher the load current, the lower the inductance of the coil should be, since higher currents

lengthen the charging time of the coil. Switching frequencies lower than 20kHz are often not desired.

It is possible (without manipulating the internal IC trimming data) to set the peak current and the average current of

the LED by a variation of sense resistor and coil value. The same can be achieved by programming a modified

parameter set to the EEPROM of the IC.

The free wheel diode that carries the load current during the passive state (driver OFF) should be a very fast

switching diode like ES1D or BYG80 with a recommended trr<30ns in order to avoid parasitic spikes on RSENSE.

The diode must be able to carry the current flowing in the LED.

For applications that use an external temperature sensor, virtually any low cost diode with a temperature coefficient

of -2mV/K can be used.

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.

A well chosen parameter set can help to avoid such a condition. The goal should be to unload the coil as much as

possible during the selected monoflop time (see as well chapter 8.3).

The schematic diagram under 1.1.1 is used in applications, where the LED is controlled by external control

electronics. A PWM with a frequency between 30Hz..4kHz can be applied to the CONTROL pin in order to

dim the light output. This frequency is limited by the debouncing time for the sleep mode on the lower side

and the selected monoflop time on the upper side of that range.

This function can be used to achieve different light outputs or also be used in a temperature down

regulation.

It is recommended to have the PWM frequency at least 5-10 times lower than the selected driver switching

frequency.

The minimum schematic diagram under 1.1.2 is sufficient for all applications with a constant light output.

Nevertheless a dimming function could be achieved by a PWM driving directly on the module supply.

In this mode, the PWM frequency should be chosen between 0 and 1kHz. It is limited by the maximum

IC settling time.