dm00059258

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
www.st.com
Contents
AN4140
Contents
1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
Component calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5
6
7
2/17
4.1
CIN selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2
COUT selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3
RSENSE value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.4
Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Output power capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1
With the LQH6PPN470M3 inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2
With the MSS1038473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3
With the LPS6235473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1
With the LQH6PPN470M3 inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2
With the MSS1038473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.3
With the LPS6235473MLB inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Doc ID 023412 Rev 1
AN4140
1
Description
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.
Doc ID 023412 Rev 1
3/17
Applications
2
AN4140
Applications
●
Mini PCs
●
PMP & PND
●
Printers
●
Game consoles.
Figure 1.
4/17
Package DFN8 (3 x 3 mm)
Doc ID 023412 Rev 1
AN4140
3
Application circuit
Application circuit
Figure 2.
Table 1.
Application schematic
List of external components
Comp.
Manufacturer
Part number
Value
L
CoilCraft
Murata
CoilCraft
LPS6235473MLB
LQH6PPN470M43
MSS1038473MLB
47 µH
CIN
Murata
GRM32ER71H106K
10 µF
1210
±10%, X7R, 50 V
COUT
Murata
GRM31CR61H225KA88L
2.2 µF
1206
±15%, X5R, 50 V
D
STMicroelectronics
STPS1L40M
1A
3.75 x 1 x 1.9 mm
40 V
0.4 Ω –
1.6 Ω
0603
RSENSE
Doc ID 023412 Rev 1
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
5/17
Component calculation
AN4140
4
Component calculation
4.1
CIN selection
It is recommended to use 10 µF as the input capacitor to achieve good stability of the device
and low noise on the VIN track.
4.2
COUT selection
It is recommended to use 2.2 µF as the optimal value of the output capacitor to get the best
compromise between output voltage ripple and load transient response.
4.3
RSENSE value
RSENSE = VREF / ILED
RSENSE sensing resistor
VREF reference voltage = 160 mV typical
ILED total LED output current
PRSENSE = RSENSE * ILED²
PRSENSE power dissipation of the sensing resistor
Table 2.
4.4
RSENSE calculated values
ILED
100
150
200
250
300
350
400
RSENSE
1.6 Ω
1.1 Ω
0.8 Ω
0.65 Ω
0.55 Ω
0.45 Ω
0.4 Ω
Inductor selection
A thin shielded inductor with a low DC series resistance of winding is recommended for this
application. To achieve a good efficiency in step-up mode, it is recommended to use an
inductor with a DC series resistance RDCL = RD / 10 [Ω, Ω, 1], where RD is the dynamic
resistance of the LED.
Equation 1
6/17
Doc ID 023412 Rev 1
AN4140
Component calculation
where:
IPEAK is peak inductor current
IOUT is current sourced at the VOUT pin
η is the efficiency of the STLD41
VOUT is output voltage at the VOUT pin
VIN is input voltage at the VBAT pin
L is inductance value of the inductor
f is the switching frequency.
Doc ID 023412 Rev 1
7/17
Output power capability
5
AN4140
Output power capability
All measurements were made at ambient temperature (24 °C) and 3 different inductors.
5.1
With the LQH6PPN470M3 inductor
Figure 3.
Current capability with the LQH6PPN470M3
AM12752v1
40
38
36
34
32
30
4.2
7
28
3.8
26
VOUT-MAX [V]
8
6
24
10
Iout = 100 mA
8
6
4.2
Iout = 150 mA
20
Iout = 200 mA
3.8
3
18
20
10
4.6
22
14
8
5
3.4
12
4.6
16
Iout = 250 mA
7
Iout = 300 mA
14
3.4
12
8
3
Iout = 350 mA
6
4.6
10
7
5
4.2
Iout = 400 mA
3.8 4.2
6
2.5
8/17
5.0
VIN [V]
Doc ID 023412 Rev 1
10.0
20.0
AN4140
With the MSS1038473MLB inductor
Figure 4.
Current capability with the MSS1038473MLB
AM12753v1
40
38
36
4.6
34
32
5
3.8
12
8
7
10
14
20
12
30
10
6
28
VOUT- MAX [V]
5.2
Output power capability
3.4
26
4.6
24
8
5
4.2
Iout = 100 mA
22
18
3
7
4.6
3.8
20
6
4.2
3.4
Iout = 150 mA
Iout = 200 mA
7
Iout = 250 mA
16
4.6
3.8
14
Iout = 300 mA
Iout = 350 mA
12
5
3
10
3
8
3.4
Iout = 400 mA
3.8 4.2
6
2.5
5.0
10.0
20.0
VIN [V]
Doc ID 023412 Rev 1
9/17
Output power capability
5.3
AN4140
With the LPS6235473MLB inductor
Figure 5.
Current capability with the LPS6235473MLB
AM12754v1
40
38
36
4.6
34
32
8
4.2
7
30
5
28
VOUT - MAX [V]
20
4.6
3.8
26
24
6
4.2
Iout = 100 mA
22
3.4
20
Iout = 150 mA
5
Iout = 200 mA
18
3
3.8
4.6
16
3.4
14
12
3
4.2
3.4
10
3
8
6
2.5
5.0
10.0
VIN [V]
10/17
Doc ID 023412 Rev 1
20.0
AN4140
Efficiency
6
Efficiency
6.1
With the LQH6PPN470M3 inductor
Eff [ %]
Figure 6.
IOUT = 100 mA with the LQH6PPN470M3
AM12755v1
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
Vout = 12 V
Vout = 14 V
Vout = 17 V
Vout = 20 V
Vout = 23 V
Vout = 25 V
Vout = 28 V
Vout = 31 V
Vout = 33 V
Vout = 36 V
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21
VIN [V ]
IOUT = 200 mA with the LQH6PPN470M3
Eff [%]
Figure 7.
AM12756v1
97.00
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
Vout = 12 V
Vout = 14 V
Vout = 17 V
Vout = 20 V
Vout = 23 V
Vout = 26 V
Vout = 28 V
Vout = 31 V
Vout = 34 V
Vout = 36 V
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21
VIN [V]
Doc ID 023412 Rev 1
11/17
Efficiency
AN4140
Eff [%]
Figure 8.
IOUT = 300 mA with the LQH6PPN470M3
AM12757v1
99.00
97.00
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
Vout = 12 V
Vout = 14 V
Vout = 17 V
Vout = 20 V
Vout = 23 V
Vout = 25 V
Vout = 28 V
Vout = 31 V
Vout = 33 V
Vout = 36 V
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21
VIN [V]
Eff [%]
Figure 9.
99.00
97.00
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
IOUT = 400 mA with the LQH6PPN470M3
AM12758v1
Vout = 9 V
Vout = 12 V
Vout = 15 V
Vout = 17 V
Vout = 20 V
Vout = 23 V
Vout = 26 V
Vout = 28 V
Vout = 31 V
Vout = 34 V
2
3
4
5
6
7
8
9
10
11
12
13
VIN [V]
12/17
Doc ID 023412 Rev 1
14
15
16
17
18
19
20
21
AN4140
With the MSS1038473MLB inductor
Eff [%]
Figure 10. IOUT = 100 mA with the MSS1038473MLB
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
AM12759v1
Vout = 9 V
Vout = 12 V
Vout = 16 V
Vout = 19 V
Vout = 22 V
Vout = 25 V
Vout = 27 V
Vout = 30 V
Vout = 33 V
Vout = 36 V
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
VIN [V]
Figure 11. IOUT = 200 mA with the MSS1038473MLB
Eff [%]
6.2
Efficiency
99.00
97.00
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
AM12760v1
Vout = 10 V
Vout = 13 V
Vout = 16 V
Vout = 19 V
Vout = 22 V
Vout = 25 V
Vout = 27 V
Vout = 30 V
Vout = 33 V
Vout = 36 V
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
VIN [V]
Doc ID 023412 Rev 1
13/17
Efficiency
AN4140
Eff [%]
Figure 12. IOUT = 300 mA with the MSS1038473MLB
99.00
97.00
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
AM12761v1
Vout = 10 V
Vout = 13 V
Vout = 17 V
Vout = 20 V
Vout = 23 V
Vout = 26 V
Vout = 28 V
Vout = 31 V
Vout = 33 V
Vout = 36 V
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
VIN [V]
Eff [%]
Figure 13. IOUT = 400 mA with the MSS1038473MLB
99.00
97.00
95.00
93.00
91.00
89.00
87.00
85.00
83.00
81.00
79.00
77.00
75.00
73.00
71.00
69.00
67.00
65.00
63.00
61.00
59.00
57.00
55.00
AM12762v1
Vout = 10 V
Vout = 13 V
Vout = 17 V
Vout = 20 V
Vout = 23 V
Vout = 26 V
Vout = 28 V
Vout = 30 V
Vout = 33 V
Vout = 36 V
2
3
4
5
6
7
8
9
10
11
12
13
VIN [V]
14/17
Doc ID 023412 Rev 1
14
15
16
17
18
19
20
21
AN4140
With the LPS6235473MLB inductor
Figure 14. IOUT = 100 mA with the LPS6235473MLB
AM12763v1
96.00
94.00
92.00
90.00
88.00
Vout = 10 V
86.00
Vout = 13 V
Eff [%]
84.00
82.00
Vout = 16 V
80.00
Vout = 19 V
78.00
Vout = 22 V
76.00
74.00
Vout = 25 V
72.00
Vout = 28 V
70.00
68.00
Vout = 30 V
66.00
Vout = 33 V
64.00
Vout = 36 V
62.00
60.00
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
VIN [V]
Figure 15. IOUT = 200 mA with the LPS6235473MLB
AM12764v1
98.00
96.00
94.00
92.00
90.00
Vout = 10 V
88.00
86.00
Vout = 13 V
84.00
Vout = 16 V
82.00
Eff [%]
6.3
Efficiency
Vout = 19 V
80.00
78.00
Vout = 22 V
76.00
Vout = 25 V
74.00
Vout = 28 V
72.00
70.00
Vout = 30 V
68.00
66.00
Vout = 33 V
64.00
Vout = 36 V
62.00
60.00
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
VIN [V]
Doc ID 023412 Rev 1
15/17
Revision history
7
AN4140
Revision history
Table 3.
16/17
Document revision history
Date
Revision
28-Aug-2012
1
Changes
Initial release.
Doc ID 023412 Rev 1
AN4140
Please Read Carefully:
Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the
right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any
time, without notice.
All ST products are sold pursuant to ST’s terms and conditions of sale.
Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no
liability whatsoever relating to the choice, selection or use of the ST products and services described herein.
No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this
document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products
or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such
third party products or services or any intellectual property contained therein.
UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED
WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS
OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
UNLESS EXPRESSLY APPROVED IN WRITING BY TWO AUTHORIZED ST REPRESENTATIVES, ST PRODUCTS ARE NOT
RECOMMENDED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING
APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY,
DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. ST PRODUCTS WHICH ARE NOT SPECIFIED AS "AUTOMOTIVE
GRADE" MAY ONLY BE USED IN AUTOMOTIVE APPLICATIONS AT USER’S OWN RISK.
Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void
any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any
liability of ST.
ST and the ST logo are trademarks or registered trademarks of ST in various countries.
Information in this document supersedes and replaces all information previously supplied.
The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners.
© 2012 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
Doc ID 023412 Rev 1
17/17
Similar pages