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| zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 1 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated 60v 550ma led driver and automotive grade description the zxld1356 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 550ma. depending upon supply voltage and external components, this can provide up to 30 watts of output power. the zxld1356 has been qualified to aecq100 grade 1 enabling operation in ambient temperatures from -40c to +125c output current can be adjusted above, or below the set value, by applying an external control signal to the 'adj' pin. enhanced output current dimming can be achieved by applying a pwm signal to the ?adj? pin. features ? typically better than 0.8% output current accuracy ? 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 ? available in thermally enhanced packages ? v-dfn3030-6 ja 44c/w ? tsot25 ja 82c/w ? available in ?green? molding compound (no br, sb) with lead free finish/ rohs compliant ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) ? zxld1356qet5ta automotive grade qualified to aec-q100 grade 1 pin assignments (top view) tsot25 i sense v in 2 1 3 4 5 adj gnd lx 1 2 34 5 6 v-dfn3030-6 (top view) lx gnd adj v in i sense gnd applications ? low voltage halogen replacement leds ? automotive lighting ? low voltage industrial lighting ? led back-up lighting ? illuminated signs ? emergency lighting ? selv lighting ? refrigeration lights notes: 1. no purposely added lead. fully eu directiv e 2002/95/ec (rohs) & 2011/6 5/eu (rohs 2) compliant. 2. see http://www.diodes.com for more in formation about diodes incorpor ated?s definitions of halogen and antimony free, "green " and lead-free. 3. halogen and antimony free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm t otal br + cl) and <1000ppm antimony compounds.
zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 2 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical applications circuit ? v in i sense lx gnd zxld1356 ad j v in (24 v) rs 0.36v 4.7f c1 gnd 100nf d1 l1 pin descriptions pin name pin number function tsot25 v-dfn3030-6 lx 1 1 drain of ndmos switch gnd 2 2, 5 ground (0v) adj 3 3 multi-function on/off and brightness control pin: ? leave floating for normal operation.(v adj = v ref = 1.25v giving nominal average output current o i outnom = 0.2v/r s ) ? drive to voltage below 0.2v to turn off output current ? drive with dc voltage (0.3v zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 4 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated thermal resistance symbol parameter rating unit tsot25 v-dfn3030-6 ja junction to ambient 82 44 c/w jb junction to board 33 ? c/w jc junction to case ? 14 c/w recommended operating conditions (@t a = +25c, unless otherwise specified.) symbol parameter min max units v in input voltage (note 4) 6 60 v t offmin minimum switch off-time 800 ns t onmin minimum switch on-time 800 ns f lx max recommended maximum operating frequency (note 5) 625 khz d lx duty cycle range 0.01 0.99 t op operating temperature range -40 +125 c notes: 4. v in > 16v to fully enhance output transistor. otherwise out current must be derated - see graphs. operation at low supply may caus e excessive heating due to increased on-resistance. tested at 7v guaranteed for 6v by design. 5. zxld1356 will operate at higher frequencies but accuracy will be affected due to propagation delays. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 5 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated electrical characteristics (v in = 24v, @t amb = +25c, unless otherwise specified.) symbol parameter condition min typ max unit v su internal regulator start-up threshold 4.85 5.2 v v sd internal regulator shutdown threshold 4.40 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 (note 6) adj pin floating, l = 68mh, 3 ledsf = 360khz 1.6 ma v sense mean current sense threshold voltage (defines led current 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 (note 7) 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 0.20 0.27 v 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 18.0 k ? i lxmean continuous lx switch current 0.55 a r lx lx switch ?on? resistance @ i lx = 0.55a 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 (*) dc brightness control range note 8 5:1 t ss start up time (see graphs for more details) 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. 2 ms f lx operating frequency (see graphs for more details) adj pin floating l= 68mh (0.36v) i out = 0.55a @ v led = 3.6v driving 3 leds 360 khz f lxmax recommended maximum operating frequency 500 khz notes: 6. static current of device is approximately 700 a, see graph, page 17. 7. 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. 8. ratio of maximum brightness to minimum brightness before shutdown v ref =1.25/0.25. v ref externally driven to 2.5v, ratio 10.1. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 6 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated 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) 0v v in 200mv 230mv 0v sense voltage v sense+ v sense- to f f to n 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 figure 2. theoretical operating waveforms operation can be best understood by assuming that the adj pi n of the device is unconnect ed 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 out put 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 ri sing voltage at the (-) input of the comparator. when this reac hes the threshold voltage (v adj ), the comparator output switches low and mn turns off. the co mparator output also drives another nmos switch, which bypasses internal resistor r3 to provide a controlled amount of hyster esis. 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, wi th 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 zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 7 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated device description (cont.) adjusting output current the device contains a low pass filter between the adj pin and the threshold comparator and an internal current limiting resisto r (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 cha nge 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 shutdown 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 volt age reference remains powered during shutdown to provide the b ias current for the shutdown circuit. quiescent supply current during shutdo wn is nominally 60a and switch leakage is below 5a. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 8 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated actual operating waveforms [v in = 15v, r s = 0.36v, l = 68h] normal operation. output current (ch3) and lx voltage (ch2) actual operating waveforms [v in = 30v, r s = 0.36v, l = 68h] normal operation. output current (ch3) and lx voltage (ch2) actual operating waveforms [v in = 60v, r s = 0.36v, l = 68h] normal operation. output current (ch3) and lx voltage (ch2) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 9 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions ? 0.5 00 output current (a) 0.5 20 0.5 40 0.5 60 0.5 80 0.6 00 0.6 20 0.6 40 15 led s 13 led s 11 l e d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supp ly voltage (v) zxld1356 output current l = 68h zxld 1356 output current deviation (normalized) l = 68h 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) 10% 8% -10% -8% -6% 6% -4% -2% 0% 2% 4% output current deviation (%) 15 leds 13 led s 11 le ds 9 leds 7 leds 5 l eds 3 l eds 1 l ed 040 50 60 10 20 30 supply voltage (v) zxld1356 efficienc y l = 68h 100% 95% 50% 55% 60% 90% 65% 70% 75% 80% 85% efficiency (%) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 10 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) zxld1356 switching frequenc y l = 68h 15 leds 13 leds 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) 700 600 500 400 300 100 200 0 switching frequency (khz) 15 leds 13 leds 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) zxld1356 duty cycle l = 68h 0 100 10 90 20 80 30 70 40 60 50 duty cycle (% ) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 11 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) ? zxld1356 output current l = 100h 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) 0.500 output current (a) 0.520 0.540 0.560 0.580 0.600 0.620 0.640 zxld1356 output current deviation (normalized) l = 100h 10% 8% -10% -8% -6% 6% -4% -2% 0% 2% 4% output current deviation (%) 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) 15 leds 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) zxld1356 efficienc y l = 100h 100% 95% 50% 55% 60% 90% 65% 70% 75% 80% 85% efficiency (%) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 12 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) zxld1356 switching frequenc y l = 100h 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) 70 0 600 500 400 300 100 200 0 switching freq uency (khz) 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) zxld1356 duty cycle l = 100h 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 13 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) ? zxld1356 output current l = 150h 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) ? 0.500 output current (a) 0.520 0.540 0.560 0.580 0.600 0.620 0.640 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) 10% 8% -10% -8% -6% 6% -4% -2% 0% 2% 4% output current deviation (%) zxld 1356 output current devi ation (n ormalized) l = 150h 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) zxld1356 efficienc y l = 150h 100% 95% 50% 55% 60% 90% 65% 70% 75% 80% 85% efficiency (%) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 14 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) ? 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) zxld1356 switching frequenc y l = 150h 700 600 500 400 300 100 200 0 switching frequency (khz) 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%) zxld1356 duty cycle l = 150h zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 15 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) zxld1356 output current l = 220h 15 led s 13 led s 11 le ds 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) ? 0.500 output current (a) 0.520 0.540 0.560 0.580 0.600 0.620 0.640 zxld 1356 output current devi ation (n ormalized) l = 220h 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) 10% 8% -10% -8% -6% 6% -4% -2% 0% 2% 4% output current deviation (%) zxld1356 efficienc y l = 220h 15 led s 13 led s 11 le d s 9 leds 7 l eds 5 leds 3 leds 1 led 040 50 60 10 20 30 supply voltage (v) 100% 95% 50% 55% 60% 90% 65% 70% 75% 80% 85% efficiency (%) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 16 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) 15 led s 13 led s 11 le d s 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) zxld1356 switching frequency l = 220h ? 700 600 500 400 300 100 200 0 switching frequency (khz) zxld1356 duty cycle l = 220h 15 led s 13 led s 11 le ds 9 leds 7 leds 5 leds 3 leds 1 led 04 0 50 60 10 20 30 supply voltage (v) 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 17 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) led current vs v ad j 0 100 200 300 400 500 600 0123 adj pin voltage (v) led current (ma) r=0.36 ? r=0.56 ? r=1.33 ? vref 1.238 1.2385 1.239 1.2395 1.24 1.2405 1.241 1.2415 1.242 1.2425 1.243 0 1 02 03 04 05 06 07 0 adj pin voltage (v) supply current 0 100 200 300 400 500 600 700 800 0 1 02 03 04 05 06 07 0 supply voltage (v) supply voltage (v) supply voltage (v) supply current ( m a) shutdown current 0 10 20 30 40 50 60 70 80 90 0 1 02 03 0 4 05 06 07 0 shutdown current ( m a) output transistor fully enhanced output transistor not fully enhanced zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 18 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated typical operating conditions (cont.) 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 die temperature (c) on-resistance (oh m s) 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) vadj (v) 7v 9v 12v 20v 30v 0 0.5 1 1.5 2 2.5 0 1 02 03 04 05 06 07 0 supply voltage (v) on-resistance (ohms) -40 o c 25 o c 125 o c lx on-resistance vs supply voltage zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 19 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information setting nominal average output current with external resistor r s 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 > 0.36? ] the table below gives values of nominal average output current for several preferred values of current setting resistor (r s ) in the typical application circuit shown on page 1: r s ( ? ) nominal average output current (ma) 0.36 555 0.56 357 1.33 150 the above values assume that the adj pin is floating and at a nominal voltage of v ref (= 1.25v). note that r s = 0.36v is the minimum allowed value of sense resistor under these c onditions to maintain switch current below 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 . gnd zxld1356 adj gnd + dc 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 550ma 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. 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 : pwm gnd 0v v adj gnd zxld1356 a dj zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 20 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) driving the adj input via open collector transistor the recommended method of driving the adj pin and controlling the am plitude of the pwm waveform is to use a small npn switching transistor as shown below: pwm gnd zxld1356 adj gnd this scheme uses the 50k resistor between the adj pin and the in ternal voltage reference as a pull-up resistor for the external transistor eg mmbt3904. 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: gnd zxld1356 adj mcu 3.3k if the nmos transistor within the microcontroller has high gate / drain capacitance, this arrangement can inject a negative spi ke into adj input of the zxld1356 and cause erratic operation but the addition of a schottky clamp diode (eg diodes inc. sd103cws) to ground and inclusion of a series resistor (3.3k) will prevent this. see the section on pw m dimming for more details of t he various modes of control usi ng high frequency and low frequency pwm signals. 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 l ow 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 17 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 capaci tance increases this delay by approximately 0.2ms/nf. the graph on the next page shows t he variation of soft-start time for different values of capa citor. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 21 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) soft-start (cont.) soft start time vs capacitance from adj pin to ground -2 0 2 4 6 8 10 12 14 16 0 2 04 06 08 01 0 01 2 0 capacitance (nf) soft start time (ms) actual operating waveforms [v in = 60v, r s = 0.36v, l = 68h, 22nf on adj] soft-start operation. lx voltage (ch2) and output current (ch3) using a 22nf external capacitor on the adj pin. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 22 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) v in capacitor selection a low esr capacitor should be used for input decoupling, as the esr of this capacitor appea rs in series with the supply source impedance and lowers overall efficiency. this capacitor has to supply the relatively high peak current to the coil and smooth the current rip ple 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 = 2.2f v in = 40 to 50v c in = 4.7f v in = 50 to 60v c in = 10f when the input voltage is close to the output voltage the input current increases which puts more demand on the input capacitor . the minimum value of 2.2f may need to be increased to 4.7f; higher values will improve performance at lower input voltages, especially wh en the source impedance is high. the input capacitor 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. capacitors w ith y5v dielectric are not suitable for dec oupling in this application and should not be used. when higher voltages are with c in = 10f, an electrolytic capacitor can be used provided that a suitable 1m f ceramic capacitor is also used and positioned as close to the v in pin as possible. a suitable capacitor would be nace w100m1006.3x8tr13f (nic components). the following web sites are useful when finding alternatives: www.murata.com www.niccomp.com www.kemet.com inductor selection recommended inductor values for the zxld1356 are in the range 68 h to 220 h. higher values of inductance are recommended at higher supply voltages in order to minimi ze errors due to switching delays, whic h result in increased ripple and lower efficiency. higher va lues of inductance also result in a smaller change in output current over the s upply voltage range. (see graphs pages 10-16). the inductor should be mounted as close to the device as po ssible with low resistance connections to the lx and v in pins. the chosen coil should have a saturation cu rrent higher than the peak output current and a continuous current rating above the required mean output current. suitable coils for use with the zxld1356 may be selected from th e mss range manufactured by coilcraft, or the npis range manufa ctured 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 ov er the supply voltage and load current range. figures 3 and 4 (following) can be used to select a recommended inductor based on maintaining the zxld1356 case temperature bel ow 60c for the different package types. for detail ed performance characteristics for the in ductor values 68, 100, 150 and 220h see gr aphs on pages 10-16. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 23 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) inductor selection (cont.) minimum recommended inductor 2% accuracy, <60c case temperature 0 1 02 03 04 05 06 0 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 figure 3. zxld1356 minimum recommended inductor diode selection for maximum efficiency and performance, the rectifier (d1) should be a fast low capac itance schottky diode* with low reverse le akage at the maximum operating voltage and temperature. they also provide better efficiency than s ilicon diodes, due to a combination of lower forward voltage and reduced recovery tim e. it is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher t han the maximum output load current. it is very important to consider the re verse leakage of the diode when operating above 85c. excess leakag e 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 l x output. if a silicon diode is used, care should be tak en to ensure that the total voltage appearing on the lx pin including supply ripple, d oes not exceed the specified maximum value. *a suitable schottky diode w ould be b1100b (diodes inc). zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 24 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) reducing output ripple peak to peak ripple current in the led(s) can be reduced, if r equired, by shunting a capacitor, cled, across the led(s) as show n below: v in v in i sense lx zxld1356 rs l1 cled led d1 a value of 1f will reduce the supply ripple current by a fact or three (approx.). proportionally lower ripple can be achieved w ith higher capacitor values. note that the capacitor will not affect operating frequenc y or efficiency, but it will increase start-up delay, by redu cing 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 wi thout 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 o ff to prevent device operation with excessive on- resistance of the output transistor. the output transistor is not full enhanced until the supply voltage exceeds approximately 17v. at supply voltages between v sd and 17v care must be taken to avoid excess ive power dissipation due to the on-resistance. note that when driving loads of two or more leds, the forward drop will normally be sufficient to prevent the device from switc hing below approximately 6v. this will minimize the risk of damage to the device. thermal considerations when operating the device at high ambient temp eratures, or when driving maximum load cu rrent, care must be taken to avoid excee ding the package power dissipation limits. the graph below gives details fo r power derating. this assumes the device to be mounted on a (25mm) 2 pcb with 1oz copper standing in still air. tsot23-5 dfn3030-6 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -40 -25 -10 5 20 35 50 65 80 95 110 125 ambient temperature (c) 140 maximum power dissipation power dissipation (w) zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 25 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) thermal considerations (cont.) note that the device power dissipation will most often be a maxi mum at minimum supply voltage. it will also increase if the eff iciency 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 o peration at all drive levels. the leds are usually mounted remotely from the devic e so, for this reason, the temperature coefficients of the i nternal circuits for the zxld1356 have been optimized to minimize the change in output current when no compensation is employed. if output current compensation is required, it is possible to use an external temperature sensing netwo rk - 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. layout considerations lx pin the lx pin of the device is a fast switching node, so pcb tr acks should be kept as short as possible. to minimize ground 'bounc e', the ground pin of the device should be solder ed directly to the ground plane. coil and decoupling capacitors and current sense resistor it is particularly important to mount the coil and the input decoup ling capacitor as close to the device pins as possible to mi nimize parasitic resistance and inductance, which will degrade effi ciency. it is also important to minimi ze any track 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 act ual 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 shor t as possible to reduce noise pickup. a 100nf capacitor from the adj pin to gr ound will reduce frequency modulation of the output under these co nditions. an additional series 3.3k ? resistor can also be used when driving the adj pin from an exte rnal circuit (see below). this resistor will provide filtering for low frequency noise and provide prot ection against high voltage transients. gnd zxld1356 adj 3.3k 100nf gnd 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 desens itize it to leakage that might raise the adj pin voltage and cause excessive out put current. however, a ground ring placed around the adj pin is recommended to minimize changes in output current under these conditions. evaluation boards zxld1356 evaluation boards are ava ilable on request, which have connection terminals that allow customers to connect their own led products to the board. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 26 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated application information (cont.) 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, causi ng the input to the shutdown circuit to fall below its turn-o ff 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 current ioutavg proportional to the pwm duty cy cle. (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: s pwm outavg r d2.0 i = for dpwm > 0.001 this mode is preferable if optimum led 'whiteness' is required. it will also provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expens e of greater output ripple. zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 27 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated ordering information device part mark package code packaging reel size (inches) reel width (mm) quantity per reel part number suffix automotive grade zxld1356dactc 1356 dac v-dfn3030-6 13 12 3000 tc ZXLD1356ET5TA 1356 et5 tsot25 7 8 3000 ta zxld1356qet5ta 1356 et5 tsot25 7 8 3000 ta y (note 9) note: 9. for automotive grade with aec-q100 grade 1 qualification the zxld1356qet5ta should be ordered. package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. v-dfn3030-6 tsot25 v-dfn3030-6 dim min max typ a 0.80 0.90 0.85 a1 0 0.05 - a3 - - 0.203 b 0.30 0.40 0.35 d 2.95 3.05 3.00 d2 1.95 2.05 2.00 e 2.95 3.05 3.00 e2 1.15 1.25 1.20 e - - 0.95 e1 - - 1.90 l 0.45 0.55 0.50 all dimensions in mm tsot25 dim min max typ a ? 1.00 ? a1 0.01 0.10 ? a2 0.84 0.90 ? d ? ? 2.90 e ? ? 2.80 e1 ? ? 1.60 b 0.30 0.45 ? c 0.12 0.20 ? e ? ? 0.95 e1 ? ? 1.90 l 0.30 0.50 l2 ? ? 0.25 0 8 4 1 4 12 ? all dimensions in mm c a1 l e1 e a2 d e1 e 5x b 4x 1 l2 a e 2 d 2 l b e a 3 a a 1 c h a m f e r 0 . 3 0 0 x 4 5 p i n # 1 i d e 1 e d s e a t i n g p l a n e zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 28 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated suggested pad layout please see ap02001 at http://www.diodes.com/dat asheets/ap02001.pdf for the latest version. v-dfn3030-6 tsot25 dimensions value (in mm) c 0.950 x 0.450 x1 2.100 y 0.630 y1 1.300 y2 3.160 dimensions value (in mm) c 0.950 x 0.700 y 1.000 y1 3.199 y1 c c x (5x) y (5x) y 1 x 1 y x c y 2 c - 0 . 3 2 9 zxld1356/ zxld1356q document number: ds33470 rev. 4 - 2 29 of 29 www.diodes.com october 2012 ? diodes incorporated zxld1356/ zxld1356q a product line o f diodes incorporated important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve the right to ma ke modifications, enhancements, im provements, corrections or ot her changes without further notice to this document and any product described herein. diodes incorporated does not assume any liability ari sing out of the application or use of this document or any product described herein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or user of this document or products described herein in such applica tions shall assume all risks of such use and will agree to hold diodes incorporat ed and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability wh atsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes inco rporated products for any unintended or unauthorized application, customers shall i ndemnify and hold diodes incorporated and its representat ives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death a ssociated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. this document is written in english but may be translated into mu ltiple languages for reference. only the english version of t his document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical comp onents in life support devices or systems without the express written approval of the chief executive offi cer of diodes incorporated. as used herein: a. life support devices or syst ems 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 inst ructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support devic e or system whose failure to perform can be reasonably expect ed to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning the ir products and any use of diodes incorporated products in such safety-critica l, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporate d and its representatives against any damages arising out of the use of diodes incorporated products in such safety-critical, life suppor t devices or systems. copyright ? 2012, diodes incorporated www.diodes.com |
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