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zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 1 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated high accuracy 1a, 60v led driver with aec-q100 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. the zxld1366 has been qualified to aecq100 grade 1 enabling operation in ambient temperatures from -40c to +125c the zxld1366 uses a high-side output current sensing circuit which uses an external resistor to set the nominal average output current. the output current can be adjusted above, or below the set value, by applying an external c ontrol signal to the 'adj' pin. enhanced output current dimming resolution can be achieved by applying a pwm signal to the ?adj? pin. soft-start can be forced using an ex ternal 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. 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 (top view) so-8ep 4 6 5 1 7 2 8 3 lx gnd gnd adj v in gnd gnd i sense typical application circuit v in i sen se lx gnd zxld1366 adj v in (24v) rs 0.2v 4.7f c1 gnd 100nf d1 l1 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%) ? switching frequencies up to 1mhz ? wide input voltage range: 6v to 60v ? inherent open-circuit led protection ? available in thermally enhanced green molding packages ? so-8ep ja = + 45c/w ? v-dfn3030-6 ja = + 44c/w ? tsot25 ja = + 82c/w ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) ? qualified to aec-q100 grade 1 ? so-8ep zxld1366en8tc ? tsot25 ZXLD1366ET5TA applications ? automotive lighting ? low voltage industrial lighting ? led back-up lighting ? illuminated signs ? emergency lighting ? selv lighting ? refrigeration lights notes: 1. eu directive 2002/95/ec (rohs) & 2011/65/eu (roh s 2) compliant. all applicable rohs exemptions applied. 2. see http://www.diodes.com for more in formation about diodes incorpor ated?s definitions of halogen- and antimony-free, "gree n" and lead-free. 3. halogen- and antimony-free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 2 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated block diagram ? low voltage dete ctor voltage regulator lx mn l1 d1 i sen se adj gn d 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 figure. 1 pin connection for tsot25 package pin description name tsot25 v-dfn3030-6 so-8ep function lx 1 1 1 drain of ndmos switch gnd 2 2, 5 2, 3, 6, 7 ground (0v) adj 3 3 4 multi-function on/off and brightness control pin: ? leave floating for normal operation.(v adj = v ref = 1.25v giving nominal average output current i outnom = 0.2v/ rs ) ? 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 4 5 connect resistor rs from this pin to vi n to define nominal average output current i outnom = 0.2v /rs . (note : r smin = 0.2v with adj pin open-circuit) v in 5 6 8 input voltage (6v to 60v). decouple to ground with 4.7f of higher x7r ceramic capacitor close to device. pad - pad pad exposed pad (ep) - connect ed to device substrate. to improve thermal impedance of package the ep must be connected to power ground but should not be used as the 0v (gnd) current path. it can be left floating but must not be connected to any other voltage other than 0v.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 3 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated absolute maximum ratings (note 4) symbol parameter rating unit v in input voltage -0.3 to +65 v v sense i sense voltage (note 5) +0.3 to -5 v v lx lx output voltage -0.3 to +65 v v adj adjust pin input voltage -0.3 to +6 v i lx switch output current 1.25 a p tot power dissipation (refer to package thermal de-rating curve on page 25) tsot25 1 w v-dfn3030-6 1.8 so-8ep 2.2 t op operating temperature -40 to +125 c t st storage temperature -55 to +150 c t j max junction temperature +150 c note: 4 all voltages unless otherwise stated are measured with respect to gnd. 5. v sense is measured with respect to v in . caution: stresses greater than the 'absolute maximum ratings' sp ecified above, may cause permanent damage to the device. these are stress ratings only; functional operation of the devic e at conditions between maximum recommended operating conditions and absolute maximum r atings is not implied. device reliability may be affected by exposure to absolute maximum rating c onditions for extended periods of time. esd susceptibility rating unit human body model 500 v machine model 75 v caution: semiconductor devices are esd sensitive and may be damaged by exposur e to esd events. suitable esd precautions should be taken when handling and transporting these devices. the human body model is a 100pf capacitor discharge through a 1.5k ? resistor pin. the machine model is a 200pf capacitor discharged directly into each pin. thermal resistance symbol parameter rating unit tsot25 so-8ep v-dfn3030-6 ja junction to ambient 82 45 44 c/w jb junction to board 33 ? ? jc junction to case ? 7 14 recommended operating conditions symbol parameter min max units v in input voltage (note 6) 6 60 v i lx maximum recommended continuous/rms switch current 1 a 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 ensure devices is off 0.25 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 8) 625 khz d lx duty cycle range 0.01 0.99 d lx(limit) recommended duty cycle range of output switch at f lxmax 0.3 0.7 t op operating temperature range -40 +125 c notes: 6. 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. 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. zxld1366 will operate at higher frequencies but accuracy will be affected due to propagation delays.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 4 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated electrical characteristics (test conditions: v in = 24v, t a = +25c, unless otherwise specified.) symbol parameter condition min typ max unit v su internal regulator start-up threshold 4.85 5.20 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 9) adj pin floating, l = 68h, 3 leds, f = 260khz 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 0.20 0.25 0.30 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 1 a r lx lx switch ?on? resistance @ i lx = 1a 0.50 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 1.000 v brightness control range 1000:1 dc adj dc brightness control range (note 8) 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 2 ms f lx operating frequency (see graphs for more details) adj pin floating l = 68h (0.2v) i out = 1a @ v led = 3.6v driving 3 leds 260 khz t onmin minimum switch ?on? time lx switch ?on? 130 t offmin minimum switch ?off? time lx switch ?off? 70 notes: 9. static current of device is approximately 700 a, see graph, page 16 10. 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. 11. 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 .
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 5 of 30 www.diodes.com may 2012 ? diodes incorporated 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 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 current sense ci rcuit 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, whic h 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
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 6 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated device description (cont.) actual operating waveforms v in = 15v, r s = 0.2 , l = 68h normal operation. output current (ch 3) and lx voltage (ch 2) v in = 30v, r s = 0.2 , l = 68h normal operation. output current (ch 3) and lx voltage (ch 2) v in = 60v, r s = 0.2 , l = 68h normal operation. output current (ch 3) and lx voltage (ch 2) 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 either 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 shutdown circuit. when the input voltage to this ci rcuit 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 current during shutdown is nominally 60 a and switch leakage is below 5 a.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 7 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions 0 10 20 30 40 50 60 supply voltage (v) output current, l = 68h 1.100 1.080 1.060 1.040 1.020 1.000 0.980 ou t p u t c u r r e n t ( a ) 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) output current deviation, l = 68h 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 1 0 8 6 4 2 0 -2 o u t p u t c u r r en t devi a t i o n (%) -4 -6 -8 -10 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) efficiency, l = 68h 100 95 90 85 80 75 70 e f f i c ien c y (%) 65 60 55 50
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 8 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) switching frequency, l = 68h 500 450 400 150 100 50 0 swi t c h in g f r e q u en c y (k h z) 350 300 250 200 1 led 3 leds 5 leds 7 leds 9 leds 11 led s 13 leds 15 leds 0 102030405060 supply voltage (v) duty cycle, l = 68h 100 90 80 30 20 10 0 d u t y c y c le (%) 70 60 50 40
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 9 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) output current, l = 100h 1.100 1.080 1.060 1.040 1.020 1.000 0.980 o ut p ut c u r r ent ( a ) 0.960 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) output current deviation, l = 100h 10 8 6 4 2 0 -2 o ut p ut c u r r ent devi a ti o n (%) -4 -6 -8 -10 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 sup ply voltage (v) efficiency, l = 100h
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 10 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 1 led 3 leds 5 leds 7 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) switching frequency, l = 100h 500 450 400 150 100 50 0 swi t c h in g f r e q u en c y (k h z) 350 300 250 200 1 led 3 leds 5 leds 7 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) duty cycle, l = 100h 100 90 80 30 20 10 0 d u t y c y c le (%) 70 60 50 40
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 11 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 0 102030405060 supply voltage (v) output current, l = 150h 1 led 3 leds 5 leds 7 leds 9 leds 11 led s 13 leds 15 leds 1.100 1.080 1.060 1.040 1.020 1.000 0.980 o ut p ut c u r r ent ( a ) 0 102030405060 supply voltage (v) output current deviation, l = 150h 10 8 6 4 2 0 -2 o u t p u t c u r r en t devi a t i o n (%) -4 -6 -8 -10 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) efficiency, l = 150h 1 led 3 leds 5 leds 7 leds 9 leds 11 led s 13 leds 15 leds
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 12 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 1 led 3 leds 5 leds 7 leds 11 led s 13 leds 15 leds 500 450 400 150 100 50 0 swi t c h in g f r e q u en c y (k h z) 350 300 250 200 01 02 03 04 05 06 0 supply voltage (v) switching frequency, l = 150h 100 90 80 30 20 10 0 d u t y c y c le (%) 70 60 50 40 0 102030405060 supply voltage (v) duty cycle, l = 150h 1 led 3 leds 5 leds 7 leds 11 leds 13 leds 15 leds
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 13 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 0 102030405060 supply voltage (v) output current, l = 220h 1.100 1.080 1.060 1.040 1.020 1.000 0.980 ou t p u t c u r r e n t ( a ) 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) output current deviation, l = 220h 10 8 6 4 2 0 -2 ou t p u t c u r r e n t d e vi a t ion ( % ) -4 -6 -8 -10 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 0 102030405060 supply voltage (v) efficiency, l = 220h 1 led 3 leds 5 leds 7 leds 9 leds 11 led s 13 leds 15 leds efficiency (%)
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 14 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 0 102030405060 supply voltage (v) switching frequency, l = 220h 500 450 400 150 100 50 0 swi t c h in g f r e q u en c y (k h z) 350 300 250 200 1 led 3 leds 5 leds 7 leds 11 led s 13 leds 15 leds 0 102030405060 supply voltage (v) duty cycle, l = 220h 100 90 80 30 20 10 0 d u t y c y c le (%) 70 60 50 40 1 led 3 leds 5 leds 7 leds 11 led s 13 leds 15 leds
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 15 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) adj pin voltage (v) led current vs. adj 03 2 1 1200 1000 800 600 400 200 0 led c u r r e n t (ma) r = 200m r = 300m r = 680m supply voltage (v) 070 50 10 20 30 40 60 800 500 400 300 200 100 0 s u p p l y c u r r e n t (ma) 600 700 supply voltage (v) 07 0 50 10 20 30 40 60 1.2430 1.2415 1.2410 1.2405 1.2400 1.2395 1.2380 adj p i n v o l t a g e (v) 1.2420 1.2425 1.2385 1.2390 supply voltage (v) 07 0 50 10 20 30 40 60 90 60 50 40 30 0 s h u t d o wn c u r r en t (ma) 70 80 10 20
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 16 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) 05 3035 10 15 20 25 supply voltage (v) lx on-resistance vs. supply voltage -40c 20c 150c 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 o n- r e s i s t a n c e ( ) 7v 9v 12v 20v 30v -50 0 200 50 100 150 temperature (c) v vs. temperature adj 1.262 1.260 1.258 1.256 1.254 1.250 1.248 1.246 1.244 v (v) adj 1.252 7v 9v 12v 30v 20v -50 0 200 50 100 150 die temperature (c) lx on-resisitance vs. die temperature 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 o n - r e s i s t a n c e ()
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 17 of 30 www.diodes.com may 2012 ? diodes incorporated 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 0.2 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) 0.20 1000 0.27 740 0.56 357 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 sense resistor under t hese conditions to maintain switch curr ent 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 . 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. output current adjustment by pwm control directly driving adj input a pulse width modulated (pwm) signal with dut y cycle dpwm can be applied to the adj pin, as shown below, to adjust the output c urrent to a value above or below the nominal average value set by resistor r s : gnd zxld1366 adj gnd + dc pw m gnd 0v v adj gnd zxld1366 adj
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 18 of 30 www.diodes.com may 2012 ? diodes incorporated 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: 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. 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 microcontroller has high gate / drain capacitance, this arr angement can inject a negative spi ke into adj input of the zxld1366 and cause erratic opera tion but the addition of a schottky clamp diode (eg diodes inc. sd103cws) to groun d 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 using high frequency and low frequency pwm signals. shutdown mode taking the adj pin to a voltage below 0.2v for more than approximately 100 s will turn off the output and supply current to a low standby level of 65 a 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). pwm gnd zxld1366 adj gnd gnd zxld1366 adj mcu 3.3k
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 19 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated application information (cont.) 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 cap acitance increases this delay by approximately 0.2ms/nf. the graph below sh ows the variation of soft-start time for different values of capacitor. 60 80 100 120 02040 capacitance (nf) soft-start time vs. capacitance form adj to ground 16 14 12 10 4 2 0 -2 8 6 s o f t -s t a r t t ime (ms) actual operating waveforms [v in = 60v, r s = 0.2 , l = 68 h, 22nf on adj] soft-start operation. lx voltage (ch2) and output current (ch3) using a 22nf external capacitor on the adj pin.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 20 of 30 www.diodes.com may 2012 ? diodes incorporated 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 appears in series with the supply source impedance and lowers overall efficiency. this capacit or 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 voltage 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 lower input voltages, especially when 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 dielectr ic 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 used with the c in = 10 f, an electrolytic capacitor can be used provided that a suit able 1f 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 zxld1366 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 sm aller change in output current over the s upply voltage range. (see graphs pages 10-17). the inductor should be mounted as close to the device as possible with low resistance connecti ons to the lx and vin pins. the chosen coil should have a saturation current higher than t he 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 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 cycl e and switch 'on'/'off' times within the specified limits ov er the supply voltage and load current range. the graph figure 3 below can be used to select a recommended i nductor based on maintaining the zxld1366 case temperature below +60c. for detailed performance characteristi cs for the inductor values 68, 100, 150 and 220 h see graphs on pages 10-17.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 21 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated application information (cont.) minimum recommended inductor 2% accuracy, <60c case temperature 0 102030405060 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 zxld1366 minimum recommended inductor (tsot25) 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 s u p p l y v o l t a g e ( v ) legend 68h 100h 150h 220h figure. 4 zxld1366 minimum recommended inductor (v-dfn3030-6)
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 22 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated application information (cont.) figure. 5 zxld1366 minimum recommended inductor (so-8ep) diode selection for maximum efficiency and performance, the rectifier (d1) shoul d be a fast low capacitance 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 would be b3100 (diodes inc). 0 1 02 03 04 05 06 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 legend 47h 68h 100h 150h 47h 68h 100h 150h t < 70c, i = 1a cl e d number of leds supply voltage (v)
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 23 of 30 www.diodes.com may 2012 ? diodes incorporated 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 shown below: figure. 6 reduced output ripple a value of 1f will reduce the supply ripple current by a factor three (approx.). proportionally lower ripple can be achieved w ith higher capacitor 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 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 forwar d 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. v in v in i sense lx zxld1366 rs l1 cled led d1
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 24 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated application information (cont.) thermal considerations when operating the device at high ambient tem peratures, or when driving maximum load curr ent, care must be taken to avoid excee ding 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. -40 -25 -10 5 20 35 50 65 80 -5 110 125 ambient temperature (c) maximum power dissipation power dissipation (w) 2. 5 2.0 1.5 1.0 0.5 0 so-8ep v-dfn3030-6 tsot25 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 t he use of unsuitable coils, or excessive paras itic output capacitance on the switch outpu t. in order to maximize the thermal capabilities of the dfn3030-6 and the so-8ep packages thermal vias should be incorporated into the pcb. see figures 7 and 8 for examples used in the zxld1366 evaluation boards. figure. 7 suggested layout for v-dfn3030-6 package
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 25 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated application information (cont.) figure. 8 suggested layout for so-8ep package vias ensure an effective path to the ground plane for the heat fl ow therefore reducing the thermal impedance between junction a nd ambient temperature. diodes came to the conclusion that the compromise is reached by using more than 10 vias with 1mm of diameter and 0 .5 hole size. finally the same scheme in figure 7 (without the exposed paddle) can be usde for the tsot25 package guaranteeing an effective t hermal path. 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 th e device so, for this reason, the temperature coefficients of th e internal circuits for the zxld1366 have been optimized to minimize the change in output current when no compensation is employed. if out put current compensation is required, it is pos sible to use an external temperature sens ing network normally using negative tempera ture coefficient (ntc) thermistors and/or diodes, mounted very close to the led(s). the out put of the sensing network can be used to drive the adj pin in order to reduce output cu rrent with increasing temperature. layout considerations lx pin the lx pin of the device is a fast switching node, so pcb tra cks should be kept as short as po ssible. to minimize ground 'bounc e', the ground pin of the device should be sol dered directly to the ground plane. coil and decoupling capacitors and current sense resistor it is particularly important to mount the coil and the input decoupling 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 minimize 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 i sense 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 actual 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 ground will reduce frequency modulat ion of the output under these conditions. an additi onal series 3.3k ? resistor can also be used when driving the adj pi n from an external circuit (see next page). this resistor will provide filtering for low frequency noise and provide protection agains t high voltage transients.
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 26 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated application information (cont.) gnd zxld1366 adj 3.3k 100nf gnd high voltage tracks avoid running any high voltage tracks close to the adj pin, to r educe 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 pcb zxld1366 evaluation boards are ava ilable on request. terminals allow users to inte rface the boards to their preferred led produ cts. 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 v adj and a low level of zero, the output of the internal low pass filter will swing between 0v and v adj , causing the input to the shutdown circui t 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 a n average output current i outavg proportional to the pwm duty cycle. (see figure 9 - 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 'whiteness' is requir ed. it will also provide the wides t possible dimming range (approx. 1000:1) and higher efficiency at the expens e of greater output ripple. v adj pwm voltage to n ioutavg 0v 0 to ff 0.2/rs ioutnom output current figure. 9 low frequency pwm operating waveforms
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 27 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated ordering information ? zxld1366 dac : v-dfn3030-6 en8 : so-8ep et5 : tsot25 tc : 13? tape & reel tc : 13? tape & reel ta : 7? tape & reel part number package packing zxld1366 xxx xx device part mark packaging reel size (inches) reel width (mm) quantity per reel part number suffix aec-q100 zxld1366dactc 1366 v-dfn3030-6 13 12 3000 tc zxld1366en8tc zxld 1366 yyww so-8ep 13 12 2500 tc grade 1 ZXLD1366ET5TA 1366 tsot25 7 8 3000 ta grade 1 where yy stands for last 2 digits of year - 10, 11 and ww stands for week number. package outline dimensions 1) tsot25 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
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 28 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated package outline dimensions (cont.) 2) so-8ep 3) v-dfn3030-6 so-8ep (sop-8l-ep) dim min max typ a 1.40 1.50 1.45 a1 0.00 0.13 - b 0.30 0.50 0.40 c 0.15 0.25 0.20 d 4.85 4.95 4.90 e 3.80 3.90 3.85 e0 3.85 3.95 3.90 e1 5.90 6.10 6.00 e - - 1.27 f 2.75 3.35 3.05 h 2.11 2.71 2.41 l 0.62 0.82 0.72 n - - 0.35 q 0.60 0.70 0.65 all dimensions in mm 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 gauge plane seating plane e1 e n e b a 45 e0 h f exposed pad bottom view l q c 7 4 3 9 (all sides) a1 d 14 85 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
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 29 of 30 www.diodes.com may 2012 ? diodes incorporated a product line o f diodes incorporated suggested pad layout 1) tsot25 2) so-8ep 3) v-dfn3030-6 dimensions value (in mm) c 0.950 x 0.700 y 1.000 y1 3.199 dimensions value (in mm) c 1.270 x 0.802 x1 3.502 x2 4.612 y 1.505 y1 2.613 y2 6.500 dimensions value (in mm) c 0.950 x 0.450 x1 2.100 y 0.630 y1 1.300 y2 3.160 y1 c c x (5x) y (5x) c y1 x1 x y y2 x2 y 1 x 1 y x c y 2 c - 0 . 3 2 9
zxld1366 zxld1366 document number: ds31992 rev. 7 - 2 30 of 30 www.diodes.com may 2012 ? diodes incorporated 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 rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product descri bed 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 di odes 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 inco rporated and all the companies wh ose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability w hatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes in corporated products for any unintended or unaut horized application, customers shall i ndemnify and hold diodes incorporated and its represent atives harmless against all claims, damages , expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated 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 mo re united states, international or foreign trademarks. life support diodes incorporated 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 officer 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 prope rly used in accordance with instructions for use provided in the labeling can be reasonably expected to re sult 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 their products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by di odes incorporated. further, customers must fully indemnify di odes incorporated and its representatives agains t any damages arising out of the use of di odes incorporated products in such safety- critical, life support devices or systems. copyright ? 2012, diodes incorporated www.diodes.com

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