? 1/8 STLD20D white led power supply preliminary data october 2004 rev. 2 features high efficiency above 80% can drive up to 4 leds in series from 2.8v supply constant led current regulation integrated led disconnect switch that cuts the leds branch in shutdown mode constant switching frequency stable current regulation across the total input voltage range supply voltage rejection inherent soft start by limiting the peak inductor current peak inductor current adjustability (STLD20D- c8 only) shutdown pin with possibility of pwm dimming control over voltage and over temperature protection with automatic restart low shutdown current < 1a small external inductor (10h, height < 2mm) tiny ceramic external capacitor can be supplied by a li-ion battery - v in range: 2.5vdc to 5vdc table 1: order codes part number marking package STLD20D-c8 l2d sot23-8l STLD20D-def l2d qfn 3x3 8l this is preliminary information on a new product now in devel opment or undergoing evaluation. details are subject to change wit hout notice. asd? figure 1: basic connection l = 10h d cout = 1f cin = 2.2f i = 20ma led r set v batt r led v out v in lds fb d: stm bat20j l: murata lqh32cn100k33 sw gnd (*) STLD20D-c8 only shdn r (*) set STLD20D application white led supply for lcd backlight mobile phone pda and organizers any handsets powered from 2.8v to 4.2v description the STLD20D is a constant switching frequency boost regulator with specific features to supply up to 4 white leds in series. a stable led current regulation, from 2.8v to 4.2v, is achieved by sens- ing the led current through a low ohmic shunt re- sistor r led (see figure 1). the device also includes a supply rejection circuit that prevent any kind of flickering effect on the display during dy- namic supply voltage variation. a led disconnect switch cut the led branch to reduce the current consumption in shutdown mode. the maximum peak inductor current can be programmed. the STLD20D includes often numerous features and in- novative design circuit that allows getting an efficien- cy above 80% across the total supply voltage range. figure 2: efficiency versus input voltage (i led =20ma; t amb =25c) 78 79 80 81 82 83 84 85 86 87 88 2.5 3 3.5 4 4.5 5 input voltage (vdc) efficiency (%)
STLD20D 2/8 figure 5: block diagram figure 3: STLD20D-c8 pin-out designation (sot23-8l top view) figure 4: STLD20D-def pin-out designation (qfn 8l top view) sw v out lds fb fb gnd v in shdn r set 12 3 4 5 6 7 8 gnd v in shdn r set fb lds v out sw gnd exposed p ad sw v in v out shdn lds n/c fb 12 3 4 5 6 7 8 gnd v in shdn n/c fb lds v out sw gnd shdn fb v in lds v out r set (*) oscillator otp ovp ramp oscillator compensation pwn comp. s q r + + + - - - power fault vin enable drain current reference led disconnect led current reference shdn vin sw lds sw (*) STLD20D-c8 only t v in
STLD20D 3/8 table 2: external components pproposal (note 1) - referred basic connection (figure 1) table 3: absolute maximum ratings symbol parameter test conditions value unit min. typ. max. r led led current resistance 15 ? c in input filtering capacitor ceramic type 2.2 f c out output capacitance 1 l boost inductor (height < 2mm) inductance 10 h resistance at 500khz 1 ? isat (r set = 100k ? )300 ma d boost diode (stmicroelectronics bat20j type) v rrm 23 vdc i f (peak forward current) 1 a v f @ i f = 0.1a tj = 25c 0.35 0.4 v i r @ tj = 25c v r = 15v 3 12 a i r @ tj = 85c v r = 15v 120 250 note 1: the external components proposal should be considered as a design reference guide. the performances mentioned in the electrical characteristics ta ble are not guaranteed for all t he possible electrical parameter s of the com- ponents included in this list. on an other hand the operation of STLD20D is not limited with the use of components included in this list. symbol parameter test conditions value unit min. typ. max. v in supply voltage range 2.5 5 v v esd esd ratings hbm mil std 883c 2 kv t op operating temperature - 40 + 85 c t stg storage temperature - 65 150 c b vds breakdown voltage at pin sw and tss and v out 20 v shdn maximum voltage applied on shdn pin v in v
STLD20D 4/8 table 4: electrical characteristics (for v in = 2.8 to 4.2v and tj = 25c) table 5: thermal characteristics symbol parameter test conditions value unit min. typ. max. v in operating input voltage range 2.8 4.2 v i out average regulated current i out = 20ma r led = 15 ? 19 20 21 ma i sd stand-by current shdn = low v in = 4.2v 1 a i q quiescent current consumption shdn = high v in = 4.2v 0.43 0.6 ma sw boost switch rdson sot23-8l tj = 25c i sw = 250ma v in = 2.8v 0.51 0.6 ? v in = 4.2v 0.45 0.49 qfn tj = 25c i sw = 250ma v in = 2.8v 0.65 v in = 4.2v 0.55 lds load disconnect switch r dson sot23-8l tj = 25c i lds = 20ma v in = 2.8v 5.5 6.1 ? v in = 4.2v 4.7 5.2 qfn tj = 25c i lds = 20ma v in = 2.8v 6.2 v in = 4.2v 5.3 fb feedback voltage 0.285 0.300 0.315 v line variation of the led current versus the input voltage: r led = 15 ? 0.9 ma/v eff efficiency with 4 leds vout = 16v circuit configura- tion (figure 1) l: murata lqh32cn100k33 diode: bat20j v in = 2.8v 80 % v in = 4.2v 85 switching frequency 400 500 600 khz dc min minimum duty cycle 22 25 % i lim peak current boost switch l = 10h r s et = gnd (STLD20D-c8) 640 ma ovp overvoltage protection 17.5 18.5 20 vdc hyst ov overvoltage hysteresis 0.7 vdc otp over temperature protection 110 c hyst ot over temperature protection hysteresis 5 c shdn shutdown signal logic disable low v il 0.3 v enable high v ih 1.2 symbol parameter value unit min. typ. max. rth(j-a) mounted on epoxy board without copper heatsink sot23-8l 300 c/w qfn 350
STLD20D 5/8 functional description 1. boost controller: the STLD20D is a pwm mode control boost con- verter operating at 500khz in discontinuous mode. an automatic compensation of the oscillation ramp allows rejection of the battery voltage transient. the led constant regulation (referred figure 4 ) is done by sensing the led current through the resistance r led ( figure 1 ). the voltage across r led is used by the feedback loop of the controller (pin fb). 2. peak inductor current limitation and soft start function: an integrated current sensor senses the peak drain current of the switch sw in order to keep the inductor current below its saturation level. since the peak drain current exceeds 590ma (if r set = gnd for STLD20D-c8), the rs flip flop turns off the switch sw. during start up, this peak drain current limitation acts inherently like a soft start function . 3. peak inductor current adjustability (STLD20D-c8 only) the peak current of the boost inductor should always be below the saturation current. in order to provide flexibility in the selection of the inductor, the maxi- mum peak inductor current can be adjusted by con- necting a resistor at the pin r set . the figure 5 gives the value of the resistance r set versus the peak in- ductor current limit i lmax at 25c. if a low ripple is es- pected on the battery voltage bus, then the maximum peak inductor current should be reduced. 4. shutdown: the shdn pin is a low logic input signal and allows turning off the controller without cutting the input volt- age from the boost regulator circuit. an integrated led disconnect switch lds disconnects the leds branch in shutdown mode .this arrangement allows eliminating the dc current path that normally exists with traditional boost regulator in shutdown mode. 5. brightness control: the brightness of the led is adjusted by pulsing the shutdown pin with a low frequency pwm signal. by using such a pwm signal the controller is alternatively on and off and the led current changes from full current to zero. the duty cycle allows to regulate the average led current . this scheme ensures that when the leds are on they are driven at the full current without risk of color change. 6. otp: an integrated temperature sensor senses the temperature of the junction of the controller. when this tem- perature exceeds 110c min fixed internally the controller is automatically turned off . when the tem- perature is reduced the operation of the device automatically recovers. figure 6: led current versus input voltage v(v) in i (ma) led 19.00 19.20 19.40 19.60 19.80 20.00 20.20 20.40 20.60 20.80 21.00 2.5 3 3.5 4 4.5 5 figure 7: r set (k ? ) versus i lmax (a) i(a) lmax r = f(i ) set lmax r(k) set ? 0 20 40 60 80 100 120 0.3 0.4 0.5 0.6 0.7 v =3.2v in v =4.2v in
STLD20D 6/8 7. over voltage protection (ovp): in case of failure and if the led branch is cut, then there is no signal at the feedback pin fb ( figure 1 ), the pwm controller will then switches with a maximum duty cycle. this will generate a voltage at the pin sw and v out that can exceed the maximum rating of the device. the overvoltage protection bloc senses the output voltage at the pin v out ( figure 1). if the voltage exceeds 18.5vdc typical the controller is automat- ically turned off. when the voltage is reduced of 0.7v, the operation of the device automatically recovers. 8. efficiency ( figure 1 & 2 ) the efficiency takes into account these following losses: r led ohmic losses boost switch sw losses led disconnect switch lds boost inductor losses boost diode losses total driver consumption. figure 8: sot23-8l package mechanical data e1 d a2 a l gauge plane seating plane < a1 c 0.25 e1 e b c e ref. dimensions millimeters inches min. max. min. max. a1.450.057 a1 0.15 0.006 a2 0.90 1.30 0.035 0.051 b 0.22 0.38 0.008 0.015 c 0.08 0.22 0.003 0.008 d 2.80 3 0.110 0.118 e 2.60 3 1.102 0.118 e1 1.50 1.75 0.059 0.069 e 0.65 typ. 0.026 typ. e1 1.95 typ. 0.077 typ. l 0.30 0.60 0.012 0.024 <0808
STLD20D 7/8 figure 9: qfn 3x3 8l package mechanical data figure 10: qfn foot print dimensions (in millimeters) l2 d1 a a1 b1 l e2 l1 d2 r r1 k b e a2 a3 l2 e 0.41 0.39 4.00 4.00 2.02 0.65 1.21 0.34 - exposed pad is not connected to the ground of the dice. - connect exposed pad to pin one. ref. dimensions millimeters inches min. typ. max. min. typ. max. a 0.80 0.90 1.00 0.031 0.035 0.039 a1 0.03 0.03 0.001 0.002 a2 0.65 0.70 0.75 0.026 0.028 0.030 a3 0.15 0.20 0.25 0.006 0.008 0.010 b 0.29 0.31 0.39 0.011 0.012 0.015 b1 0.17 0.30 0.007 0.012 d 3.00 0.118 d2 1.92 2.02 2.12 0.076 0.079 0.083 e 3.00 0.118 e2 1.11 1.21 1.31 0.044 0.048 0.051 e 0.65 0.026 k 0.20 0.008 l 0.20 0.29 0.45 0.008 0.011 0.018 l1 0.16 0.24 0.40 0.006 0.009 0.016 l2 0.13 0.005 r 0.15 0.006 r1 0.15 0.006
STLD20D 8/8 information furnished is believed to be accurate and reliable. however, stmicroelectronics assu mes no responsibility for the co nsequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publicati on are subject to change without notice. this publication supersedes and replac es all information previously supplied. stmicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectro nics. the st logo is a registered tr ademark of stmicroelectronics. all other names are the property of their respective owners ? 2004 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 - singapore - spain - sweden - switzerland - united kingdom - united states of america www.st.com table 6: ordering information part number marking package weight base qty delivery mode STLD20D-c8 l2d sot23-8l 0.2 g 3000 tape & reel STLD20D-def l2d qfn 3x3 8l 0.22 g 3000 tape & reel table 7: revision history date revision description of changes august-2004 1 first issue 12-oct-2004 2 table 4 on page 4 following parameters values updated: . i out (min), i q (min), sw (qfn max), lds (qfn max), i lim , hyst ot . fb var symbol changed to line and value changed from 0.7 to 0.9 ma/v
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