MLX10803_06 Datasheet, PDF (5/25 Pages) List of Unclassifed Manufacturers – High power LED driver

IC specification MLX10803
High power LED driver
1.1.3. Principle soft start up LED driver diagram
Cap for EMC directly
on the connector
100nF...1uF
VBAT
100nF
VREF
ROSC
IREF1
IREF2
VS/PWM
DRVGATE
GND
RSENSE
GND
Figure 3: Application with gradual increase of light intensity after power up (soft start)
1.1.4. 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).
To reduce an influence of noise which can be coupled to sensitive reference pins IREF1, IREF2 it is possible to
connect noise-filtering capacitors in parallel to IREF1 and IREF2 resistors (see Figure 1, Cnoise capacitors). The
coupling also should be reduced as much as possible by proper routing of IREF1 and IREF2 stripes on PCB. IREF2
3901010803
Rev 024
Page 5/25
Data Sheet
7/DEC/06