ST AN2333 Application note
AN2333
Application note
White LED power supply for large display backlight
Introduction
This application note is dedicated to the STLD40D, it's a boost converter that operates from
3.0 V to 5.5 V dc and can provide an output voltage as high as 37 V
10 white LEDs in series.
Figure 1. Package
and can drive up to
DC
Figure 2. Pin configuration
June 2011 Doc ID 12202 Rev 3 1/9
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Contents AN2333
Contents
1 Schematic description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Selection of external components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Input and output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 LED selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 PCB design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 PCB design rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2/9 Doc ID 12202 Rev 3
AN2333 Schematic description
1 Schematic description
The converter is a PFM (pulse frequency modulation) inductor switcher and can work in
discontinuous (DCM) as well as continuous (CCM) Mode operation. The output current
capability is 20 mA with an output voltage of 37Vdc.The regulation is done by sensing the
LED current through resistor R
enable signal pin EN. By applying a low frequency PWM signal the WLEDs can be dimmed.
.The device can be turned ON/OFF through the logic
LED
The maximum peak inductor current can be programmed by connecting a resistor R
pin R
SET
.
1.1 Application schematic
Figure 3. Typical application schematic
SET
to
Doc ID 12202 Rev 3 3/9
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