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issue 2 - september 2008 1 www.zetex.com ? diodes incorporated 2008 www.diodes.com a product line of diodes incorporated ZXLD1366 high accuracy 1a, 60v led dr iver with internal switch description the ZXLD1366 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected leds efficiently from a voltage source higher than the led voltage. the device operates from an input supply between 6v and 60v and provides an externally adjustable output current of up to 1a. depending upon supply voltage and external components, this can provide up to 48 watts of output power. the ZXLD1366 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. output current can be adjusted above, or below the set value, by applying an external control signal to the 'adj' pin. the adj pin will accept either a dc voltage or a pwm waveform. depending upon the control frequency, this will pr ovide either a continuous (dimmed) or a gated output current. soft-start can be forced using an external capacitor from the adj pin to ground. applying a voltage of 0.2v or lower to the adj pin turns the output off and switches the device into a low current standby state. features ? typically better than 0.8% output current accuracy ? available in thermally enhanced dfn package ? simple and with low part count ? single pin on/off and brightness control using dc voltage or pwm ? pwm resolution up to 1000:1 ? high efficiency (up to 97%) ? wide input voltage range: 6v to 60v ? inherent open-circuit led protection applications ? low voltage halogen replacement leds ? automotive lighting ? low voltage industrial lighting ? led back-up lighting ? illuminated signs ? emergency lighting ? selv lighting ? lcd tv backlighting ? refrigeration lights pin connections typical application circuit lx tsot23-5 top view 1 2 3 5 4 gnd adj v in dfn633 top view lx gnd adj gnd i sense i sense v in v in i sense lx gnd ZXLD1366 adj v in (24v) rs 0.2 4.7 f c1 gnd 100nf d1 l1 www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 2 www.zetex.com ? diodes incorporated 2008 www.diodes.com absolute maximum ratings (voltages to gnd unless otherwise stated) electrical characteristics (test conditions: v in =24v, t amb =25c unless otherwise stated) (a) notes: (a) production testing of the device is pe rformed at 25c. functional operation of the device and parameters specified over a -40c to +105c temperature range, are guaranteed by design, characterization and process control. (b) v in > 16v to fully enhance output transistor. otherwise out current must be derated - see graphs. operation at low supply may cause excessive heating due to increased on-resistance. tested at 7v guaranteed for 6v by design. (c) static current of devi ce is approximately 700 a, see graph, page 17 (d) 100% brightness corresponds to v adj = v adj(nom) = v ref . driving the adj pin above v ref will increase the v sense . threshold and output current proportionally. input voltage (v in ) -0.3v to +60v (65v for 0.5 sec) i sense voltage (v sense ) +0.3v to -5v (measured with respect to v in ) lx output voltage (v lx ) -0.3v to +60v (65v for 0.5 sec) adjust pin input voltage (v adj )-0.3v to +6v switch output current (i lx ) 1.25a power dissipation (p tot ) (refer to package thermal de-rating curve on page 26) sot23-5; 1w: dfn; 1.8w operating temperature (t op ) -40 to 125c storage temperature (t st ) -55 to 150c junction temperature (t j max )150c these are stress ratings only. operatio n outside the absolute maximum ratings may cause device failure. operation at the absolute maximum ratings, for extended periods, may reduce device reliability. thermal resistance tsot23-5 dfn junction to ambient (r ja ) 82c/w 44c/w junction to board (r jb ) 33c/w - junction to case (r jc )- 14c/w symbol parameter conditions min. typ. max. unit v in input voltage see note (b) 660v v su internal regulator start-up threshold 4.85 5.2 v v sd internal regulator shut down threshold 4.4 4.75 v i inqoff quiescent supply current with output off adj pin grounded 65 108 a i inqon quiescent supply current with output switching (c) adj pin floating, l=68 h, 3 leds, f = 260khz 1.6 ma v sense mean current sense threshold voltage (defines led curren t setting accuracy) measured on i sense pin with respect to v in v adj = 1.25v; v in =18v 195 200 205 mv v sensehys sense threshold hysteresis 15 % i sense i sense pin input current v sense = v in -0.2 4 10 a v ref internal reference voltage measured on adj pin with pin floating 1.25 v v ref / t temperature coefficient of v ref 50 ppm/c v adj external control voltage range on adj pin for dc brightness control (d) 0.3 2.5 v v adjoff dc voltage on adj pin to switch device from active (on) state to quiescent (off) state v adj falling 0.15 0.2 0.27 v www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 3 www.zetex.com ? diodes incorporated 2008 www.diodes.com electrical characteristics (test conditions: v in =24v, t amb =25c unless otherwise stated) ( cont.) symbol parameter conditions min. typ. max. unit v adjon dc voltage on adj pin to switch device from quiescent (off) state to active (on) state v adj rising 0.2 0.25 0.3 v r adj resistance between adj pin and v ref 0< v adj < v ref v adj > v ref +100mv 30 10.4 50 14.2 65 18 k k i lxmean continuous lx switch current 1 a r lx lx switch ?on? resistance @ i lx = 1 a 0.5 0.75 i lx(leak) lx switch leakage current 5 a d pwm(lf) duty cycle range of pwm signal applied to adj pin during low frequency pwm dimming mode pwm frequency <300hz pwm amplitude = v ref measured on adj pin 0.001 1 brightness control range 1000:1 dc adj (*) notes: (*) ratio of maximum brightness to minimum brightness before shutdown v ref = 1.25/0.3. v ref externally driven to 2.5v, ratio 10:1. dc brightness control range see note (*) 5:1 t ss soft start time time taken for output current to reach 90% of final value after voltage on adj pin has risen above 0.3v requires external capacitor 22nf. see graphs for more details 2ms f lx operating frequency (see graphs for more detail) adj pin floating l = 68 h (0.2 ) i out = 1a @ v led = 3.6v driving 3 leds 260 khz t onmin minimum switch ?on? time lx switch ?on? 130 (?) (?) parameters are not tested at production. parameters are guaranteed by design, characterization and process control. ns t offmin minimum switch ?off? time lx switch ?off? 70 (?) ns t pwmin_rec recommended minimum switch pulse width lx switch 'on' or ?off? 800 ns f lxmax recommended maximum operating frequency 500 khz d lx recommended duty cycle range of output switch at f lxmax 0.3 0.7 www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 4 www.zetex.com ? diodes incorporated 2008 www.diodes.com pin description ordering information name pin no. description lx 1 drain of ndmos switch gnd 2 ground (0v) adj 3 multi-function on/off a nd brightness control pin: ? leave floating for normal operation.(v adj = v ref = 1.25v giving nominal average output current i outnom = 0.2v/r s ) ? drive to voltage below 0.2v to turn off output current ? drive with dc voltage (0.3v < v adj < 2.5v) to adjust output current from 25% to 200% of i outnom ? connect a capacitor from this pin to ground to set soft-start time. soft start time increases approximately 0.2ms/nf i sense 4 connect resistor r s from this pin to v in to define nominal average output current i out nom = 0.2v/r s ( note: r smin = 0.2 with adj pin open-circuit) v in 5 input voltage (6v to 60v). decouple to ground with 4.7 f or higher x7r ceramic capacitor close to device tab not internally connected. connect to ground plane to improve thermal efficiency device reel size (inches) reel width (mm) quantity per reel device mark ZXLD1366et5ta 7? 8 3,000 1366 ZXLD1366dactc 13? 12 3,000 1366 lx tsot23-5 top view 1 2 3 5 4 gnd adj v in dfn633 top view lx gnd adj gnd i sense i sense v in www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 5 www.zetex.com ? diodes incorporated 2008 www.diodes.com figure 1 block diagram - pin connection for tsot package low voltage detector voltage regulator lx mn l1 d1 i sense adj gnd v in v in 50k 20k 1.25v 1.35v 0.2v 600khz + - + - + - r4 r5 r2 r3 r1 2 3 54 1 d1 + - r s c1 4.7 f 5v www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 6 www.zetex.com ? diodes incorporated 2008 www.diodes.com device description the device, in conjunction with the co il (l1) and current sense resistor (r s ), forms a self- oscillating continuous-mode buck converter. device operation (refer to figure 1 - block diagram and figure 2 operating waveforms) operation can be best understood by assuming that the adj pin of the device is unconnected and the voltage on this pin (v adj ) appears directly at the (+) input of the comparator. when input voltage v in is first applied, the initial current in l1 and r s is zero and there is no output from the current sense circuit. under this condition, the (-) input to the comparator is at ground and its output is high. this turns mn on and switches the lx pin low, causing current to flow from v in to ground, via r s , l1 and the led(s). the current rises at a rate determined by v in and l1 to produce a voltage ramp (v sense ) across r s . the supply referred voltage v sense is forced across internal resistor r1 by the curr ent sense circuit and produces a proportional current in internal resistors r2 and r3. this produces a ground referred rising voltage at the (-) input of the comparator. when this reaches the threshold voltage (v adj ), the comparator output switches low and mn turns off. the comparator output also drives another nmos switch, which bypasses internal resistor r3 to provide a controlled amount of hysteresis. the hysteresis is set by r3 to be nominally 15% of v adj . when mn is off, the current in l1 continues to flow via d1 and the led(s) back to v in . the current decays at a rate determined by the led(s) and diode forward voltages to produce a falling voltage at the input of the comparator. when this voltage returns to v adj , the comparator output switches high again. this cycle of events repeats, with the comparator input ramping between limits of v adj 15%. switching thresholds with v adj = v ref , the ratios of r1, r2 and r3 define an average v sense switching threshold of 200mv (measured on the i sense pin with respect to v in ). the average output current i outnom is then defined by this voltage and r s according to: i outnom = 200mv/r s nominal ripple current is 30mv/r s adjusting output current the device contains a low pass filter between the adj pin and the threshold comparator and an internal current limiting resistor (50k nom) between adj and the internal reference voltage. this allows the adj pin to be overdriven with ei ther dc or pulse signals to change the v sense switching threshold and adjust the output current. details of the different modes of adjusting output current are given in the applications section. output shutdown the output of the low pass filter drives the shutdo wn circuit. when the input voltage to this circuit falls below the threshold (0.2v nom.), the internal regulator and the output switch are turned off. the voltage reference remains powered during shutdown to provide the bias current for the shutdown circuit. quiescent supply cu rrent during shutdown is nominally 60 a and switch leakage is below 5 a. www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 7 www.zetex.com ? diodes incorporated 2008 www.diodes.com figure 2 theoretical operating waveforms 0v v in 200mv 230mv 0v sense voltage v sense+ v sense- toff ton 170mv 0v 5v v in 0.15v adj 0.15v adj i outnom i outnom +15% i outnom -15% v adj lx voltage coil current comparator input voltage comparator output www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 8 www.zetex.com ? diodes incorporated 2008 www.diodes.com actual operati ng waveforms [v in =15v, r s =0.2 , l=68h] normal operation. output current (ch3) and lx voltage (ch2) actual operati ng waveforms [v in =30v, r s =0.2 , l=68h] normal operation. output current (ch3) and lx voltage (ch2) actual operati ng waveforms [v in =60v, r s =0.2 , l=68h] normal operation. output current (ch3) and lx voltage (ch2) www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 9 www.zetex.com ? diodes incorporated 2008 www.diodes.com intentionally left blank www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 10 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 output current l=68h 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0102030405060 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 102030405060 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=68h ZXLD1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0 102030405060 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=68h www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 11 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 switching frequency l=68h 0 50 100 150 200 250 300 350 400 450 500 0 102030405060 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 duty cycle l=68h 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0102030405060 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 12 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 output current 0.960 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0102030405060 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0102030405060 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 102030405060 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=100h l=100h l=100h www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 13 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 switching frequency l=100h 0 50 100 150 200 250 300 350 400 450 500 0 102030405060 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 duty cycle l=100h 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 102030405060 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 14 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 output current l=150h 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0102030405060 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0102030405060 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0102030405060 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=150h l=150h www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 15 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 switching frequency l=150h 0 50 100 150 200 250 300 350 400 450 500 0 102030405060 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 duty cycle l=150h 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0102030405060 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 16 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 output current 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0102030405060 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0 102030405060 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds ZXLD1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 102030405060 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=220h l=220h l=220h www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 17 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions ZXLD1366 switching frequency l=220h 0 50 100 150 200 250 300 350 400 450 500 0 102030405060 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0102030405060 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=220h ZXLD1366 duty cycle www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 18 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions led current vs vadj 0 200 400 600 800 1000 1200 0123 adj pin voltage (v) led current (ma) r=200m r=300m r=680m vref 1.238 1.2385 1.239 1.2395 1.24 1.2405 1.241 1.2415 1.242 1.2425 1.243 0 1020 3040 5060 70 adj pin voltage (v) supply current 0 100 200 300 400 500 600 700 800 0 10203040506070 supply voltage (v) supply voltage (v) supply voltage (v) supply current ( a) shutdown current 0 10 20 30 40 50 60 70 80 90 0 102030 40506070 shutdown current ( a) output transistor fully enhanced output transistor not fully enhanced www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 19 www.zetex.com ? diodes incorporated 2008 www.diodes.com typical operating conditions lx on-resistance vs die temperature 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -50 0 50 100 150 200 e temperature c n-resstance ms 7v 9v 12v 20v 30v vadj vs temperature 1.244 1.246 1.248 1.25 1.252 1.254 1.256 1.258 1.26 1.262 -50 0 50 100 150 200 temperature c vad v 7v 9v 12v 20v 30v 0 0.5 1 1.5 2 2.5 010203040506070 -40 o c 25 o c 125 o c lx on-resistance vs supply voltage on-resistance (ohms) supply voltage (v) www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 20 www.zetex.com ? diodes incorporated 2008 www.diodes.com application notes setting nominal average output current with external resistor rs the nominal average output current in the led(s) is determined by the value of the external current sense resistor (r s ) connected between v in and i sense and is given by: i outnom = 0.2/r s [for r s 0.2 ] the table below gives values of nominal average output current for several preferred values of current setting resistor (r s ) in the typical applicatio n circuit shown on page 1: the above values assume that the adj pin is floating and at a nominal voltage of v ref (=1.25v). note that r s = 0.2 is the minimum allowed value of se nse resistor under these conditions to maintain switch current belo w the specified maximum value. it is possible to use different values of r s if the adj pin is driven from an external voltage. (see next section). output current adjustment by external dc control voltage the adj pin can be driven by an external dc voltage (v adj ), as shown, to adjust the output current to a value above or below the nominal average value defined by r s . the nominal average output current in this case is given by: i outdc = (v adj /1.25) x (0.2/r s ) [for 0.3< v adj <2.5v] note that 100% brightness setting corresponds to v adj = v ref . when driving the adj pin above 1.25v, r s must be increased in proportion to prevent i outdc exceeding 1a maximum. the input impedance of the adj pin is 50k 25% for voltages below v ref and 14.2k 25% for voltages above v ref +100mv. r s ( ) nominal average output current (ma) 0.20 1000 0.27 740 0.56 357 gnd ZXLD1366 adj gnd + dc www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 21 www.zetex.com ? diodes incorporated 2008 www.diodes.com output current adjustment by pwm control directly driving adj input a pulse width modulated (pwm) signal with duty cycle d pwm can be applied to the adj pin, as shown below, to adjust the output current to a value above or below the nominal average value set by resistor r s : driving the adj input via open collector transistor the recommended method of driving the adj pin and controlling the amplitude of the pwm waveform is to use a small npn switching transistor as shown below: this scheme uses the 50k resistor between the adj pin and the internal voltage reference as a pull-up resistor for the external transistor. driving the adj input from a microcontroller another possibility is to drive the device from the open drain output of a microcontroller. the diagram below shows one method of doing this: if the nmos transistor within the microcontro ller has high gate / drain capacitance, this arrangement can inject a negative spike into adj input of the ZXLD1366 and cause erratic operation but the addition of a schottky clam p diode (eg diodes inc. sd103cws) to ground and inclusion of a series resistor (3.3k) will prevent this. see the section on pwm dimming for more details of the various modes of control usi ng high frequency and low frequency pwm signals. pwm gnd 0v v adj gnd ZXLD1366 adj pwm gnd ZXLD1366 adj gnd gnd ZXLD1366 adj mcu 3.3k www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 22 www.zetex.com ? diodes incorporated 2008 www.diodes.com shutdown mode taking the adj pin to a voltage below 0.2v for more than approximately 100s will turn off the output and supply current to a low standby level of 65a nominal. note that the adj pin is not a logic input. taking the adj pin to a voltage above v ref will increase output current above the 100% nominal average value. (see page 18 graphs for details). soft-start an external capacitor from the adj pin to ground will provide a soft-start delay, by increasing the time taken for the voltage on this pin to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. adding capacitance increases this delay by approximately 0.2ms/nf. the graph below shows the variation of soft-start time for different values of capacitor. actual operating waveforms [v in =60v, r s =0.2 , l=68h, 22nf on adj] soft-start operation. lx voltage (ch2) and output current (ch3) using a 22nf external capacitor on the adj pin. soft start time vs capacitance from adj pin to ground -2 0 2 4 6 8 10 12 14 16 020406080100120 capacitance (nf) soft start time (ms) 2 3 ch3 500ma ch 2 20.0v m 400s 5.0 s/s a ch2 \ 12.0 v 200 ns/pt www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 23 www.zetex.com ? diodes incorporated 2008 www.diodes.com v in capacitor selection a low esr capacitor should be used for input dec oupling, as the esr of this capacitor appears in series with the supply source impedance and lo wers overall efficiency . this capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. to avoid transients into the ic, the size of the input capacitor will depend on the v in voltage: v in = 6 to 40v c in = 2.2 f v in = 40 to 50v c in = 4.7 f v in = 50 to 60v c in = 10 f when the input voltage is close to the output vo ltage the input current increases which puts more demand on the input capacitor. the minimum value of 2.2 f may need to be increased to 4.7 f; higher values will improve performance at lowe r input voltages, especially when the source impedance is high. the input ca pacitor should be placed as close as possible to the ic. for maximum stability over temperature and voltage, capacitors with x7r, x5r, or better dielectric is recommended. capaci tors with y5v dielectric are not suitable for decoupling in this application and should not be used. when higher voltages are used with the c in = 10 f, an electrolytic capacitor can be used provided that a suitable 1 f ceramic capacitor is also used and positioned as close to the v in pin as possible. a suitable capacitor would be nacew100m1006.3x8tr13f (nic components). the following web sites are useful when finding alternatives: www.murata.com www.niccomp.com www.kemet.com www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 24 www.zetex.com ? diodes incorporated 2008 www.diodes.com inductor selection recommended inductor values for the ZXLD1366 are in the range 68 h to 220 h. higher values of inductance are recommended at hi gher supply voltages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. higher values of inductance also result in a smaller change in output current over the supply voltage range. (see graphs pages 10-17). the inductor should be mounted as close to the device as possible with low resistance connections to the lx and v in pins. the chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean output current. suitable coils for use with the ZXLD1366 may be selected from the mss range manufactured by coilcraft, or the npis range manufactured by nic components. the following websites may be useful in finding suitable components www.coilcraft.com www.niccomp.com www.wuerth-elektronik.de the inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the specified limits over the supply voltage and load current range. the graph figure 3 below can be used to select a recommended inductor based on maintaining the ZXLD1366 case temperature below 60c. for detailed performance characteristics for the inductor values 68, 100, 150 and 220h see graphs on pages 10-17. figure 3 ZXLD1366 minimum recommended inductor (tsot) minimum recommended inductor 2% accuracy, <60c case temperature 0102030405060 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 number of leds supply voltage (v) legend 68uh 100uh 150uh 220uh www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 25 www.zetex.com ? diodes incorporated 2008 www.diodes.com figure 4 ZXLD1366 minimum recommended inductor (dfn) diode selection for maximum efficiency and performance, the rectifier (d1) should be a fast low capacitance schottky diode* with low reverse leakage at the maximum operating voltage and temperature. they also provide better efficiency than silicon diodes, due to a combination of lower forward voltage and reduced recovery time. it is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. it is very important to consider the reverse leakage of the diode when operating above 85c. excess leakage will increase the power dissipation in the device and if close to the load may create a thermal runaway condition. the higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the lx output. if a silicon diode is used, care should be taken to ensure that the total voltage appearing on the lx pin including supply rippl e, does not exceed the specified maximum value. *a suitable schottky diode would be b3100 (diodes inc). minimum recommended inductor 2% accuracy, <60c case temperature 0.00 10.00 20.00 30.00 40.00 50.00 60.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 number of leds supply voltage (v) legend 68h 100h 150h 220h www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 26 www.zetex.com ? diodes incorporated 2008 www.diodes.com reducing output ripple peak to peak ripple current in the led(s) can be reduced, if required, by shunting a capacitor cled across the led(s) as shown below: a value of 1 f will reduce the supply ripple current by a factor three (approx.). proportionally lower ripple can be achieved with higher capacito r values. note that the capacitor will not affect operating frequency or efficiency, but it will increase start-up delay, by reducing the rate of rise of led voltage. by adding this capacitor the current waveform through the led(s) changes from a triangular ramp to a more sinusoidal version without altering the mean current value . operation at low supply voltage below the under-voltage lockout threshold (v sd ) the drive to the output transistor is turned off to prevent device operation with excessive on-resistance of the output transistor. the output transistor is not full enhanced until the suppl y voltage exceeds approximately 17v. at supply voltages between v sd and 17v care must be taken to avoid excessive power dissipation due to the on-resistance. if the supply voltage is always less than 30v continuous (or less than 40v for less than 0.5s) an alternative device is available, the zxld1360. note that when driving loads of two or more le ds, the forward drop will normally be sufficient to prevent the device from switching below approximately 6v. this will minimize the risk of damage to the device. thermal considerations when operating the device at high ambient te mperatures, or when driving maximum load current, care must be taken to avoid exceeding the package power dissipation limits. the graph below gives details for power derating. this assumes the device to be mounted on a 25mm 2 pcb with 1oz copper standing in still air. v in v in i sense lx ZXLD1366 rs l1 cled led d1 www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 27 www.zetex.com ? diodes incorporated 2008 www.diodes.com note that the device power dissipation will most often be a maximum at minimum supply voltage. it will also increase if the efficiency of the circuit is low. this may result from the use of unsuitable coils, or excessive parasitic output capacitance on the switch output. thermal compensation of output current high luminance leds often need to be supplied with a temperature compensated current in order to maintain stable and reliable operation at all drive levels. the leds are usually mounted remotely from the device so, for this reason, the temperature coefficients of the internal circuits for the ZXLD1366 have been optimized to minimize the change in output current when no compensation is employed. if output current compen sation is required, it is possible to use an external temperature sensing network - normally using negative temperature coefficient (ntc) thermistors and/or diodes, mounted very close to the led(s). the output of the sensing network can be used to drive the adj pin in order to reduce output current with increasing temperature. maximum power dissipation 0 200 400 600 800 1000 1200 1400 1600 1800 2000 -50 -30 -10 10 30 50 70 90 110 130 150 ambient temperature (deg c) power (mw) tsot dfn www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 28 www.zetex.com ? diodes incorporated 2008 www.diodes.com layout considerations lx pin the lx pin of the device is a fast switching node, so pcb tracks should be kept as short as possible. to minimize ground 'bounce', the ground pin of the device should be soldered directly to the ground plane. coil and decoupling capacitors and current sense resistor it is particularly important to mount the coil a nd the input decoupling capa citor as close to the device pins as possible to minimize parasiti c resistance and inductance, which will degrade efficiency. it is also important to minimize any tr ack resistance in series with current sense resistor r s . its best to connect v in directly to one end of r s and isense directly to the opposite end of r s with no other currents flowing in these tracks. it is important that the cathode current of the schottky diode does not flow in a track between r s and v in as this may give an apparent higher measure of current than is actu al because of track resistance. adj pin the adj pin is a high impedance input for voltages up to 1.35v so, when left floating, pcb tracks to this pin should be as short as possible to reduce noise pickup. a 100nf capacitor from the adj pin to ground will reduce frequency modulation of the output under these conditions. an additional series 3.3k resistor can also be used when driving the adj pin from an external circuit (see below). this resistor will provide filter ing for low frequency noise and provide protection against high voltage transients. high voltage tracks avoid running any high voltage tracks close to the adj pin, to reduce the risk of leakage currents due to board contamination. the adj pin is soft-clamped for voltages above 1.35v to desensitize it to leakage that might raise the adj pin voltage and cause excessive output current. however, a ground ring placed around the adj pin is recommended to minimize changes in output current under these conditions. evaluation pcb ZXLD1366 evaluation boards are available on re quest. terminals allow for interfacing to customers own led products. gnd ZXLD1366 adj 3.3k 100nf gnd www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 29 www.zetex.com ? diodes incorporated 2008 www.diodes.com dimming output current using pwm low frequency pwm mode when the adj pin is driven with a low frequency pwm signal (eg 100hz), with a high level voltage vadj and a low level of zero, the output of the internal low pass filter will swing between 0v and vadj, causing the input to the s hutdown circuit to fall below its turn-off threshold (200mv nom) when the adj pin is low. this will cause the output current to be switched on and off at the pwm frequency, resulting in an average output curre nt ioutavg proportional to the pwm duty cycle. (see figure 4 - low frequency pwm operating waveforms). figure 4 low frequency pwm operating waveforms the average value of output current in this mode is given by: i outavg 0.2d pwm /r s [for d pwm >0.001] this mode is preferable if optimum led 'whitene ss' is required. it will also provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expense of greater output ripple. v adj pwm voltage to n ioutavg 0v 0 to f f 0.2 / rs ioutnom output current www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 30 www.zetex.com ? diodes incorporated 2008 www.diodes.com package outline - tsot23-5 note: controlling dimensions are in millimeters. ap proximate dimensions are provided in inches dim millimeters inches min. max. min. max. a - 1.00 - 0.0393 a1 0.01 0.10 0.0003 0.0039 a2 0.84 0.90 0.0330 0.0354 b 0.30 0.45 0.0118 0.0177 c 0.12 0.20 0.0047 0.0078 d 2.90 bsc 0.114 bsc e 2.80 bsc 0.110 bsc e1 1.60 bsc 0.062 bsc e 0.95 bsc 0.0374 bsc e1 1.90 bsc 0.0748 bsc l 0.30 0.50 0.0118 0.0196 l2 0.25 bsc 0.010 bsc a 4 12 4 12 www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 31 www.zetex.com ? diodes incorporated 2008 www.diodes.com package outline - dfn633 note controlling dimensions in millimetres. ap proximate dimensions are provided in inches dim millimeters inches dim millimeters inches min. max. min. max. min. max. min. max. a 0.700 0.800 0.0275 0.0315 d2 1.950 2.050 0.0768 0.0807 a1 0.000 0.050 0.000 0.00197 e 0.950 bsc 0.0374 bsc a3 0.203 ref 0.008 e 2.950 3.050 0.116 0.120 b 0.300 0.400 0.0118 0.0157 e2 1.150 1.250 0.0452 0.0492 d 2.950 3.050 0.116 0.120 e1 1.900ref 0.0748 l 0.450 0.550 0.0177 0.0216 top view bottom view pin 1 dot by marking side view chamfer 0.300x45 pin #1 identification d a a3 a1 b d2 e e e2 e1 l www.datasheet.co.kr datasheet pdf - http://www..net/
ZXLD1366 issue 2 - september 2008 32 www.zetex.com ? diodes incorporated 2008 www.diodes.com diodes zetex sales offices europe zetex gmbh kustermann-park balanstra?e 59 d-81541 mnchen germany telefon: (49) 89 45 49 49 0 fax: (49) 89 45 49 49 49 europe.sales@zetex.com americas zetex inc 700 veterans memorial highway hauppauge, ny 11788 usa telephone: (1) 631 360 2222 fax: (1) 631 360 8222 usa.sales@zetex.com asia pacific diodes zetex (asia) ltd 3701-04 metroplaza tower 1 hing fong road, kwai fong hong kong telephone: (852) 26100 611 fax: (852) 24250 494 asia.sales@zetex.com corporate headquarters diodes incorporated 15660 n. dallas parkway suite 850, dallas, x57248, usa telephone: (1) 972 385 2810 www.diodes.com ? 2008 diodes incorporated 2008 definitions product change diodes incorporated reserves the right to alter, without notice, specifications, desi gn, price or conditions of supply of any p roduct or service. customers are solely responsible for obtaining th e latest relevant information before placing orders. applications disclaimer the circuits in this design/application note are offered as desi gn ideas. it is the responsibility of the user to ensure that t he circuit is fit for the user?s application and meets with the user?s requirements. no representation or warranty is given and no liability whatsoev er is assumed by diodes inc. with respect to the accuracy or use of such information, or infringement of patents or other intellectua l property rights arising from such use or otherwise. diodes inc. does not assume any legal responsibility or will not be held legally lia ble (whether in contract, tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential loss in the use of these circuit applications, under any circumstances. life support diodes inc. products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the chief executive office r of diodes incorporated. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body or 2. support or sustain life and whose failure to perform when proper ly used in accordance with instructions for use provided in t he labelling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support devi ce or system whose failure to pe rform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. reproduction the product specifications contained in this publication are issu ed to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the pr oducts or services concerned. terms and conditions all products are sold subjects to diodes inc. terms and conditio ns of sale, and this disclaimer (save in the event of a conflic t between the two when the terms of the contract shall prevail) accordi ng to region, supplied at the time of order acknowledgement. for the latest information on technology, delivery terms and condi tions and prices, please contact your nearest diodes sales of fice. quality of product diodes zetex semiconductors limited is an iso 9 001 and ts16949 certified semiconductor manufacturer. to ensure quality of service and products we strongly advise th e purchase of parts directly from diodes zetex or one of our reg ionally authorized distributors. for a complete listi ng of authorized distributors please visit: www.zetex.com or www.diodes.com diodes inc does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales cha nnels. esd (electrostatic discharge) semiconductor devices are susceptible to damage by esd. suitab le precautions should be taken when handling and transporting dev ices. the possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. the extent of damage can vary from immediate functional or parametric malfunc tion to degradation of function or performance in use over ti me. devices suspected of being affected should be replaced. green compliance diodes inc. is committed to environmental excellence in al l aspects of its operations which includes meeting or exceeding reg ulatory requirements with respect to the use of hazardous substances. nu merous successful programs have been implemented to reduce the use of hazardous substances and/or emissions. all diodes zetex components are co mpliant with the rohs directive, and through this it is supporting its customers in their com pliance with weee and elv directives. product status key: ?preview? future device intended for production at some point. samples may be available ?active? product status recommended for new designs ?last time buy (ltb)? device will be discontinued and last time buy period and delivery is in effect ?not recommended for new designs? device is still in production to support existing designs and production ?obsolete? production ha s been discontinued datasheet status key: ?draft version? this term denotes a very early datasheet ver sion and contains highly provisional information, which may change in any manner without notice. ?provisional version? this term denotes a pre-release datasheet. it provides a clear indication of anticipated performance. however, changes to the test conditions and specif ications may occur, at any time and without notice. ?issue? this term denotes an issued datasheet cont aining finalized specifications. however, changes to specifications may occur, at any time and without notice. www.datasheet.co.kr datasheet pdf - http://www..net/

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