AN4140
Application note
STLD41 output power capability
Introduction
This application note is dedicated to the output power capability of the STLD41, which is a
white LED driver for display backlight. The schematic, functional description and external
components selection are also discussed in this application note.
Detailed behavior, if different LED counts on the output and different currents through LEDs
are used, is also shown.
August 2012
Doc ID 023412 Rev 1
1/17
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Contents
AN4140
Contents
1
2
3
4
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Component calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1
4.2
4.3
4.4
C
IN
selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
C
OUT
selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
R
SENSE
value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5
Output power capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1
5.2
5.3
With the LQH6PPN470M3 inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
With the MSS1038473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
With the LPS6235473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1
6.2
6.3
With the LQH6PPN470M3 inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
With the MSS1038473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
With the LPS6235473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2/17
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AN4140
Description
1
Description
The STLD41 is a boost converter that operates from 3.0 V to 21 V and can provide an
output voltage as high as 38 V. It can drive up to 40 white LEDs connected in 4 strings of 10
LEDs in series. The total output current capability is 120 mA at an output voltage of 38 V.
Regulation is performed by the internal error amplifier which works with the feedback
voltage from the sensing resistor.
The device can be turned ON/OFF by way of the logic signal connected to the EN pin. The
Enable pin allows the device to be turned off, so reducing the current consumption to less
than 1 µA.
The LEDs can be dimmed by applying a PWM signal to the PWM pin.
Soft-start with controlled inrush current limit, thermal shutdown and overvoltage protection
are integrated functions of the device.
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Applications
AN4140
2
Applications
●
●
●
●
Mini PCs
PMP & PND
Printers
Game consoles.
Package DFN8 (3 x 3 mm)
Figure 1.
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AN4140
Application circuit
3
Application circuit
Figure 2.
Application schematic
Table 1.
Comp.
L
C
IN
C
OUT
D
R
SENSE
List of external components
Manufacturer
CoilCraft
Murata
CoilCraft
Murata
Murata
STMicroelectronics
Part number
LPS6235473MLB
LQH6PPN470M43
MSS1038473MLB
GRM32ER71H106K
GRM31CR61H225KA88L
STPS1L40M
Value
47 µH
10 µF
2.2 µF
1A
0.4
Ω
–
1.6
Ω
Size
Ratings
6 x 6 x 3.5 mm I = 1.2 A, DCR = 0.245
Ω
6 x 6 x 4.3 mm I = 1.25 A, DCR = 0.23
Ω
10 x 10 x 3.8 mm I = 2.22 A, DCR = 0.13
Ω
1210
1206
3.75 x 1 x 1.9 mm
0603
±10%, X7R, 50 V
±15%, X5R, 50 V
40 V
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