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february 2011 doc id 010005 rev 1 1/23 23 STLA02 white led driver for display backlight features boost dc-dc converter drives up to 6 leds with a total current up to 20 ma output power capab ility up to 500 mw input voltage range 2.5 v to 18 v output current control 2.3 mhz switching frequency pwm input for the output current dimming with 300:1 dimming range 350 ma integrated switch overvoltage protection chip overtemperature detection and protection soft-start implemented package dfn6 2 x 2 mm applications pda and handheld devices cellular phones mp3 players description STLA02 is a boost converter that operates from 2.5 v to 18 v and can provide an output voltage as high as 27 v and can drive up to 6 white leds connected in series. the total output current capability is 20 ma at an output voltage of 24 v. the total output power cap ability is up to 500 mw. the regulation is done by the internal error amplifier which works with the feedback voltage from the sensing resistor connected in high side sensing configuration. the device can be turned on/off by the logic signal connected to the en pin and this pin is also dedicated for the pwm dimming of the output current. current mode control of the regulation allows a fast response to a change of the enable pin voltage level. dfn6 (2 x 2 mm) table 1. device summary part number order code package STLA02 STLA02pur dfn6 (2 x 2 mm) www.st.com
contents STLA02 2/23 doc id 010005 rev 1 contents 1 diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1 pwm input (en) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.2 selection of the external components . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 9 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
STLA02 diagram doc id 010005 rev 1 3/23 1 diagram figure 1. block diagram vlx vin en/ pwm fb step-up control vbg logic vset reference vset vbg 12 v/5 v conv ovp bias vout gnd fb sensing ilim ilim am07827v1 vlx vin en/ pwm fb step-up control vbg logic vset reference vset vbg 12 v/5 v conv ovp bias vout gnd fb sensing ilim ilim am07827v1
pin configuration STLA02 4/23 doc id 010005 rev 1 2 pin configuration figure 2. pin connections (top view) table 2. pin description pin n symbol name and function 1v in supply voltage pin 2 gnd ground 3 lx switching pin 4v out output voltage pin 5 fb feedback voltage 6 en/pwm enable pin or pwm control input for dimming exposed pad gnd ground
STLA02 maximum ratings doc id 010005 rev 1 5/23 3 maximum ratings note: absolute maximum ratings are those values beyond which damage to the device may occur. functional operation under these conditions is not implied. table 3. absolute maximum ratings symbol parameter value unit v in signal supply voltage - 0.3 to 19 v v lx inductor connection - 0.3 to 30 v fb feedback connection (1) 1. the maximum acceptable difference between the v out pin potential and feedback pin potential is 5 v. - 0.3 to 30 v en/pwm logic pin/pwm input - 0.3 to 12 v v out output voltage connection - 0.3 to 30 v p tot continuous power dissipation (at t a = 70 c) (1) 530 mw t op operating ambient temperature range - 40 to 85 c t j junction temperature - 40 to 150 c t stg storage temperature range - 65 to 150 c table 4. thermal data symbol parameter value unit r thja thermal resistance junction-ambient (1) 102 c/w 1. power dissipation is dependent on pcb. the recommended pcb design is included in this document (tbd). table 5. esd symbol parameter value unit hbm human body model 2 kv mm machine model 200 v
application STLA02 6/23 doc id 010005 rev 1 4 application note: above listed components refer to a typical application with maximum performance settings. operation of the STLA02 is not limited to the choice of these external components. figure 3. application schematic v in l c out en/pwm c in STLA02 r fb en/pwm vin vlx vout fb gnd i led am07828v1 v in l c out en/pwm c in STLA02 r fb en/pwm vin vlx vout fb gnd i led am07828v1 table 6. list of external components component manufacturer part number value size c in murata grm216r61e105ka12 1 f / 25 v 0805 c out murata grm216r61e105ka12 1 f / 25 v 0805 l murata lqh3npn100nj0l 10 h 3x3x0.9 mm tdk vlf3012st-100mr5 9 10 h 3x2.8x1.2 mm r fb tyco cpf0402b10re 10 0402 led osram lwl283-q1r2-3k8l-1-z 20 ma / 3.1 v 0603
STLA02 electrical characteristics doc id 010005 rev 1 7/23 5 electrical characteristics v en = v in = 3 v t a = - 40 c to 85 c unless otherwise specified. typical values are at t a = 25 c, unless otherwise specified. table 7. electrical characteristics symbol parameter test conditions min. typ. max. unit v in input operating supply voltage 2.5 18 v i s supply current v en = v in , v out = 24 v, v fb = 23 v 2 4 ma v en = gnd 10 a i o output current adjustment v in = 2.5 v to 18 v, r fb = 10 20 ma v out regulated voltage range v in = 2.5 v to 18 v v in +1 27 v i peak inductor peak current v in = 2.5 v 300 400 550 ma v fb feedback voltage (v out - v fb ) v en = v in , r fb = 10 190 200 210 mv i fb fb bias current v en = v in , v out = 24 v, v fb = 24 v 6 a i lx(leak) n-mos leakage current v en = 0, v lx = v out = 24 v 0.1 a i o output current tolerance v in = 3 v, i out = 0.2 v / r fb -5 5 % f s switching frequency v in = 2.5 v, t a = 25 c 1.7 2 2.3 mhz d max maximum duty cycle v en = v in , v out = 24 v, v fb = 24 v 88 92 % r dson -n internal n-channel r dson i lx = 20 ma 0.8 efficiency of the chip itself v in = 10 v, i o = 20 ma, v o = 6 x v fled_max + v rsense = 24 v (1) 85 % efficiency of the whole application v in = 10 v, i o = 20 ma, v o = 6 x v fled_max + v rsense = 24 v (1) 83 % ovp output overvoltage protection v in = 3 v, no load 28 v t shdn thermal shutdown 130 150 c t hys thermal shutdown hysteresis 15 c v il low and high level input logic signal on en pin v in = 2.5 v to 18 v, v enmax = 12 v 01.5 v v ih 1.8 v in t en led current rise time i led = 0 to i led = 20 ma v in = 9 v, v en = 0 v to 3 v 6 leds in series (1) 0.2 ms t response led current rise time i led = 0 ma to i led = 20 ma v in = 9 v, v en = 0 v to 3 v, 6 leds in series (1) , v out precharged 60 s 1. guaranteed by design, but not tested in production.
typical performance characteristics STLA02 8/23 doc id 010005 rev 1 6 typical performance characteristics figure 4. efficiency at 20 ma current load 50 53 56 59 62 65 68 71 74 77 80 83 86 89 92 2 3 4 5 6 7 8 9 10 11 12 13 14 15 v in [v] eff [%] 0 50 100 150 200 STLA02 20 ma / 18 v eff. in [ma] am07819v1 i in [ma] 50 53 56 59 62 65 68 71 74 77 80 83 86 89 92 2 3 4 5 6 7 8 9 10 11 12 13 14 15 v in [v] eff [%] 0 50 100 150 200 STLA02 20 ma / 18 v eff. in [ma] am07819v1 i in [ma] figure 5. quiescent current vs. v in 0 5 10 15 20 0 2 4 6 8 101214161820 v in [v] i in [a] am07820v1 0 5 10 15 20 0 2 4 6 8 101214161820 v in [v] i in [a] am07820v1
STLA02 typical performance characteristics doc id 010005 rev 1 9/23 figure 6. STLA02 driver current consumption vs. v in 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 v in [v] i in [ma] 25c -40c +85c am07821v1 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 v in [v] i in [ma] 25c -40c +85c am07821v1 figure 7. switching frequency vs. temperature 1 , 9 1 , 9 2 1 , 9 4 1 , 9 6 1 , 9 8 2 -60 -40 -20 0 20 40 60 80 100 temp [c] f [mhz] am07822v1 1 , 9 1 , 9 2 1 , 9 4 1 , 9 6 1 , 9 8 2 -60 -40 -20 0 20 40 60 80 100 temp [c] f [mhz] am07822v1
typical performance characteristics STLA02 10/23 doc id 010005 rev 1 figure 8. switching frequency vs. v in @ p out = 0.36 w 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 234567891011121314 v in [v] f [mhz] am07823v1 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 234567891011121314 v in [v] f [mhz] am07823v1 figure 9. overvoltage protection threshold vs. v in 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 v in [v] v out [v] am07824v1 25.0 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 v in [v] v out [v] am07824v1
STLA02 typical performance characteristics doc id 010005 rev 1 11/23 figure 10. overvoltage protection threshold vs. temp 2 5 . 0 2 5 . 5 2 6 . 0 2 6 . 5 2 7 . 0 2 7 . 5 2 8 . 0 2 8 . 5 2 9 . 0 2 9 . 5 3 0 . 0 -40-30-20-100 1020304050607080 temp [c] v out [v] am07825v1 2 5 . 0 2 5 . 5 2 6 . 0 2 6 . 5 2 7 . 0 2 7 . 5 2 8 . 0 2 8 . 5 2 9 . 0 2 9 . 5 3 0 . 0 -40-30-20-100 1020304050607080 temp [c] v out [v] am07825v1 figure 11. output current regulation vs. v in 17.0 17.2 17.4 17.6 17.8 18.0 18.2 18.4 18.6 18.8 19.0 19.2 19.4 19.6 19.8 20.0 20.2 20.4 20.6 20.8 21.0 0 2 4 6 8 10 12 14 16 18 v in [v] i out [ma] am07826v1 17.0 17.2 17.4 17.6 17.8 18.0 18.2 18.4 18.6 18.8 19.0 19.2 19.4 19.6 19.8 20.0 20.2 20.4 20.6 20.8 21.0 0 2 4 6 8 10 12 14 16 18 v in [v] i out [ma] am07826v1
typical performance characteristics STLA02 12/23 doc id 010005 rev 1 figure 12. switching waveform at v in = 2.5 v figure 13. switching waveform at v in = 7 v figure 14. switching waveform at v in = 12 v figure 15. overvoltage function vlx vout iout il vlx vout iout il vlx vout iout il vlx vout iout il vlx vout iout il vlx vout iout il il vout vlx il vout vlx figure 16. line transient response v in = 3.4 v to 4 v step vlx vin iout il vlx vin iout il
STLA02 typical performance characteristics doc id 010005 rev 1 13/23 figure 17. direct pwm dimming 300 hz at v bat = 2.5 v, v en = 0 to 3 v step
introduction STLA02 14/23 doc id 010005 rev 1 7 introduction the STLA02 is a boost converter dedicated to powering and controlling the current of white leds in an lcd backlight. the device operates at a typical constant switching frequency of 2.3 mhz. it steps an input voltage ranging from 2.5 v to 18 v, up to 27 v. the output current is adjustable by the resistor r fb connected between the v out and fb pins. the STLA02 device contains high side sensing to simplify the pcb layout in terms of connection of the leds. the output current is dimmable by the pwm signal applied to the en pin with minimum pwm frequency equal 100 hz. 7.1 pwm input (en) light intensity can be dimmed by a signal applied to the pwm (en) input. the pwm signal is directly connected to th e enable pin of the STLA02. it is recommended to use the frequency of the pwm signal in the range of 100 hz to 1 khz and amplitude of the signal 1.8 v min. the result of the dire ct pwm dimming method (300 hz pwm and v en = 1.8 v) is shown in figure 17 . note: when the device is required to operate in a constant current mode with the en pin connected to the voltage higher than 1.8 v, then the delay between rise times of v in voltage of the device and the en voltage is mandatory to guarantee the proper internal reset of the logic of the device during ramping of the v in . it is recommended to delay the en voltage rise time by 2 ms after the rise time on v in appears. 7.2 selection of the external components c in selection it is recommended to use 1 f as the input capacitor to achieve good stability of the device and low noise on the v in track. c out selection it is recommended to use 1 f as the optimal value of output capacitor to get the best compromise between output voltage ripple and l oad transients response. the output ripple can be checked according to the equation for step-up architecture: equation 1 inductor selection a thin shielded inductor with a low dc series winding resistance 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 r dcl = r d /10 [ ; ; 1], where r d is the dynamic resistance of the led [ ; ; 1]. ( ) [] hz , f , v , a ; v f v c 100 * v v i v 2 out out ) min ( in out ) max ( out pk pk ? ? ? ? = ?
STLA02 introduction doc id 010005 rev 1 15/23 for nominal operation, the peak inductor current can be calculated by the formula: equation 2 where: i peak peak inductor current i out current sourced at the v out pin efficiency of the STLA02 v out output voltage at the v out pin v in input voltage at the v in pin l inductance value of the inductor f switching frequency for the optimal function of the STLA02 device, it is recommended to use the inductor value 10 h and higher with low serial resistance and relevant saturation current calculated from the equation above. r fb value r fb = v fb / i led in the case of a typical setting i led = 20 ma, v fb = 200 mv, and r sense = 10 . the resistor must be rated for a power di ssipation of 10 x 0.022 w = 0.004 w. pcb layout STLA02 is a powerful switched device, the pc b must be designed in line with rules for designing switched supplies. it is recommended to use a two layer pcb. the power wirings must be as short as possible and wide. place all external components close to the STLA02. high-energy switched loops should be as sma ll as possible to reduce emi. most leds need cooling, which may be done by a defined area of copper on the pcb. use the reference guide of each led to design the heatsink. place the r fb resistor as close as possible to pin 4 and 5. when a change of pcb layer is need ed, use enough vias. during routing the pcb must be focused on the minimum area of the application ground - the smaller the ground area of the dc-dc converter (a) , the better stability and lower noise issues are achieved. it is recommended to place the copper plate, conne cted through the vias to the exposed pad, on the bottom layer to create the heatsink of the device. a. the application ground area is represented by the area which is created by the ground pins of the c in , c out , ground of the device and gnd connection of the load. () [ ] in out 2 out 2 in in out out peak v v v f l 2 v v v i i ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? =
introduction STLA02 16/23 doc id 010005 rev 1 figure 18. top layer figure 19. bottom layer
STLA02 introduction doc id 010005 rev 1 17/23 figure 20. top overlay
package mechanical data STLA02 18/23 doc id 010005 rev 1 8 package mechanical data in order to meet environmental requirements, st offers these devices in different grades of ecopack ? packages, depending on their level of environmental compliance. ecopack specifications, grade definitions, an d product status are available at www.st.com . ecopack is an st trademark.
STLA02 package mechanical data doc id 010005 rev 1 19/23 table 8. dfn6 (2 x 2 mm.) mechanical data dim. mm. min. typ. max. a 0.700.750.80 a1 0 0.02 0.05 a3 0.20 b 0.180.250.30 d 1.902.002.10 d2 1.35 1.50 1.60 e 1.902.002.10 e2 0.15 0.30 0.40 e0.50 l 0.250.350.45 figure 21. dfn6 (2 x 2 mm.) drawing 7733060d
package mechanical data STLA02 20/23 doc id 010005 rev 1 table 9. dfn6 (2 x 2 mm.) tape and reel mechanical data dim. mm. inch. min. typ. max. min. typ. max. a 180 7.087 c 12.8 13.2 0.504 0.519 d 20.2 0.795 n 60 2.362 t 14.4 0.567 ao 2.3 0.091 bo 2.3 0.091 ko 1.0 0.039 po 4 0.157 p 8 0.315 figure 22. dfn6 (2 x 2 mm.) tape and reel drawing
STLA02 package mechanical data doc id 010005 rev 1 21/23 figure 23. dfn6 (2 x 2 mm) footprint recommended data
revision history STLA02 22/23 doc id 010005 rev 1 9 revision history table 10. document revision history date revision changes 22-feb-2011 1 initial release
STLA02 doc id 010005 rev 1 23/23 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 he rein 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 as sumes 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. i f 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 whatsoev er 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 parti cular 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 an authorized st representative, st products are not recommended, authorized or warranted for use in milita ry, 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 whatsoev er, 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. ? 2011 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - belgium - brazil - canada - china - czech republic - finland - france - germany - hong kong - india - israel - ital y - japan - malaysia - malta - morocco - philippines - singapore - spain - sweden - switzerland - united kingdom - united states of america www.st.com

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