MLX10801 datasheet(23/41 Pages) MELEXIS

23 / 41 page

IC specification

MLX10801

Power LED driver for automotive applications

Power saving low side coil driver

Electronic fuse

3901010801

Page 23/41

Rev 021

14/July/05

Author: TFR

revised: RAH/SSZ

jitter mode

8.3.

Coil inductance, EMI and selected parameter set

The inductance L of a coil describes the amount of magnetical energy that can be stored in it.

Consequently, high inductive coils will be discharged less than low inductive coils in a given time.

Generally the coil can be driven in two different ways:

The coil will only be discharged partially. That means the coil still carries a significant amount of energy

when going from discharging to charging. In that moment the charging current rises immediately to

the coil current that was flowing just before switching. This is connected with large dI/dt transients

on the RSENSE pin that have a negative impact on EMI.

The coil will be discharged completely. Thus, at the end of a discharging cycle, the coil doesn’t carry energy

anymore. With the next charging cycle, current increases steadily from around zero. This way,

large dI/dt transients are completely avoided.

Care has to be taken when working in jitter mode. In this case, monoflop time (=discharging time) is

not constant but varies in a certain range (see chapter 14.2 for details). It must be ensured that only

the longest possible monoflop time completely discharges the coil. Otherwise the coil is discharged

before the monflop time ends which results in a loss of efficiency.

Imax1

Iavg

tmon1

tmon2

Imax2

Conclusion: In most cases the coil is driven in a combination of both ways. A tradeoff has to be made between

EMI behaviour and maximum allowed LED current. By varying these parameters, an optimum can be found for

virtually every application.

MLX10801 Datenblatt(PDF) 23 Page - Melexis Microelectronic Systems