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ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 1 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated 60v 1a led driver with aec-q100 description the ZXLD1362 is a continuous mode inductive step- down converter with integrated switch and high side current sense. it operates from an input supply from 6v to 60v driving single or multiple series connected leds efficiently externally adjustable output current up to 1ma. the ZXLD1362 has been qualified to aec-q100 grade 1 enabling operation in ambient temperatures from -40 to 125c. the output current can be adjusted by applying a dc voltage or a pwm waveform. 100.1 adjustment of output current is possible using pwm control. applying 0.2v or lower to the adj pin turns the output off and switches the device into a low current standby state. pin assignments features ? simple low parts count ? single pin on/off and brightness control using dc voltage or pwm ? high efficiency (up to 95%) ? wide input voltage range: 6v to 60v ? up to 1mhz switching frequency ? qualified to aec-q100 grade 1 ? thermally enhanced tsot23-5: ja 82c/w ? typical 2% output current accuracy typical application circuit ? v in i se n s e lx gnd ZXLD1362 adj v in (24v) r s 0.1v 4.7f c1 gnd 100nf d1 68m l1 i sense v in adj gnd lx tsot23-5 top view
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 2 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated block diagram figure 1. block diagram pin description name pin no. description lx 1 drain of ndmos switch gnd 2 ground (0v) adj 3 multi-function on/off and br ightness control pin: ? leave floating for normal operation.(v adj = v ref = 1.25v giving nominal average output current o i outnom = 0.1/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 increase 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 outnom = 0.1/r s (note: r smin =0.1 ? with adj pin open circuit) v in 5 input voltage (6v to 60v). decouple to ground with 4.7f of higher x7r ceramic capacitor close to device 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 4.7mf 5v
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 3 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated absolute maximum ratings (voltages to gnd unless otherwise stated) symbol parameter rating unit v in input voltage -0.3 to +60 (65v for 0.5 sec) v v sense i sense voltage +0.3 to -5 (measured with respect to v in ) v v lx lx output voltage -0.3 to +60 (65v for 0.5 sec) 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 16) 1 w t st storage temperature -55 to 150 c t j max junction temperature 150 c these are stress ratings only. operation above the absolute maxi mum rating may cause device failure. operation at the absolute maximum ratings, for extended periods, may reduce device reliability. esd susceptibility rating unit human body model 500 v machine model 75 v semiconductor devices are esd sensitive and may be damaged by expos ure 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 ja junction to ambient 82 c/w jb junction to board 33 c/w recommended operating conditions symbol parameter min max units v in input voltage range (note 1) 6 60 v t offmin minimum switch off-time 800 ns t onmin minimum switch on-time 800 ns f lxma x recommended maximum operating frequency (note 2) 625 khz t op operating temperature range -40 125 c notes: 1. 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. 2. ZXLD1362 will operate at higher frequencies but accuracy will be affected due to propagation delays.
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 4 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated electrical characteristics (test conditions: v in = 24v, t a = 25c, unless otherwise specified.) (a) symbol paramete r condition min. typ. max. unit v su internal regulator start-up threshold 4.85 v v sd internal regulator shutdown threshold 4.75 v i inqoff quiescent supply current with output off adj pin grounded 65 90 a i inqon quiescent supply current with output switching (note 3) adj pin floating, l=68mh, 3 leds, f=260khz 1.8 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 95 100 105 mv v sensehys sense threshold hysteresis 10 % i sense i sense pin input current v sense = v in -0.1 4 10 a v ref internal refe rence 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 4 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 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? i lxmean continuous lx switch current 1 a r lx lx switch ?on? resistance @ i l x = 1a 0.5 1.0 ? 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 5 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=68mh (0.1v) i out =1a @ v led =3.6v driving 3 leds 300 khz t onmin minimum switch ?on? time lx switch ?on? 130 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 notes: 3. static current of device is approximately 700a, see graph, page 16. 4. 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. 5. 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.
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 5 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated device description the device, in conjunction with the coil (l1) and current sense resistor (rs), fo rms 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 gr ound and its output is high. this turns mn on and switch es 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 circuit and produces a proportio nal current in internal resistors r2 and r3. this produces a ground referred rising voltage at t he (-) input of the compar ator. when this reaches the threshold voltage (v adj ), the comparator output swit ches low and mn turns off. the comparator ou tput 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 10% 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 produc e a falling voltage at the input of the comparator. when this voltage returns to v adj , the comparator output switches hi gh again. this cycle of events repeats, with the comparator input ramping between limits of v adj 10%. switching thresholds with v adj = v ref , the ratios of r1, r2 and r3 define an average v sense switching threshold of 100mv (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 = 100mv/r s nominal ripple current is 10mv/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. th is 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 give n 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 re gulator and the output switch are turned off. the voltage re ference remains powered during shutdown to provide the bias current for the shutdown circui t. quiescent supply current during shutdown is nominally 60 a and switch leakage is below 5 a.
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 6 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated device description (continued) figure 2. theoretical operating waveforms
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 7 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated device description (continued) actual operating waveforms [v in =15v, r s =0.1v, l=100h] normal operation. output current (ch1) and lx voltage (ch2) actual operating waveforms [v in =30v, r s =0.1v, l=100h] normal operation. output current (ch1) and lx voltage (ch2) actual operating waveforms [v in =60v, r s =0.1v, l=100h] normal operation. output current (ch1) and lx voltage (ch2)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 8 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics ? 0 70 40 50 60 10 20 30 ZXLD1362 output current l = 68h supply voltage (v) 15 led 13 led 11 le d 9 led 7 led 5 led 3 l ed 1 led 1000 11 00 1010 1090 1020 1080 1030 1070 1040 1060 1050 output current (ma) 0 70 40 50 60 10 20 30 ZXLD1362 output current l = 68h supply voltage (v) 10% output current deviation -10% 8% -8% -6% -4% -2% 0% 6% 4% 2% 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 100% efficiency (%) 50% 60% 70% 90 % 80% 0 70 40 50 60 10 20 30 supply voltage (v) 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led ZXLD1362 efficienc y l = 68h
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 9 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ZXLD1362 switching frequenc y l = 68h 500 switching frequency (khz) 0 100 200 400 300 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ZXLD1362 duty cycle l = 68h 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 10 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ? 1000 11 00 1010 1090 1020 1080 1030 1070 1040 1060 1050 output current (ma) 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ZXLD1362 output current l = 100h ZXLD1362 output current l = 100h 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) -10% 10% -8% 8% -6% 6% -4% 4% -2% 2% 0% output current deviation 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ZXLD1362 efficienc y l = 100h 100% efficiency (%) 50% 60% 70% 90% 80%
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 11 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ? ZXLD1362 switching frequency l = 100h 500 switching frequency (khz) 0 100 200 400 300 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ZXLD1362 switching frequenc y l = 100h 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 12 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ZXLD1362 output current l = 150h ? 1000 11 00 1010 1090 1020 1080 1030 1070 1040 1060 1050 output current (ma) 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ZXLD1362 output current l = 150h -10% 10% -8% 8% -6% 6% -4% 4% -2% 2% 0% output current deviation 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ZXLD1362 efficienc y l = 150h 100% efficiency (%) 50% 60% 70% 90% 80%
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 13 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ? ZXLD1362 switching frequenc y l = 150h 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 500 switching frequency (khz) 0 100 200 400 300 ZXLD1362 duty cycle l = 150h 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 14 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ZXLD1362 output current l = 220h 15 led 13 led 11 le d 9 led 7 led 5 led 3 l ed 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 1000 11 00 1010 1090 1020 1080 1030 1070 1040 1060 1050 output current (ma) zxld13 62 output c urrent l = 220h -10% 10% -8% 8% -6% 6% -4% 4% -2% 2% 0% output current deviation 15 led 13 led 11 l e d 9 l ed 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supp ly voltage (v) 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 100% efficiency (%) 50% 60% 70% 90% 80% ZXLD1362 efficienc y l = 220h
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 15 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) ? ZXLD1362 switching frequency l = 2200h 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) ? 500 switching frequency (khz) 0 100 200 400 300 ZXLD1362 duty cycle l = 2200h 15 led 13 led 11 le d 9 led 7 led 5 led 3 led 1 led 0 70 40 50 60 10 20 30 supply voltage (v) 0 100 10 90 20 80 30 70 40 60 50 duty cycle (%)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 16 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (cont.) led current vs v ad j 0 200 400 600 800 1000 1200 0123 adj pin voltage (v) led current (ma) r=100m ? r=150m ? r=330m ? 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 0 3 04 0 5 06 0 7 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) shutdow n 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)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 17 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated typical characteristics (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 te mpe ra ture (c) on-resistance (oh m s) 7v 9v 12v 20v 30v lx on-resistance vs supply voltage 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 5 10 15 20 25 30 35 supply voltage (v) on-resistance (ohms) -40c 20c 150c 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
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 18 of 28 www.diodes.com december 2010 ? 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 th e 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 = 0.1/r s [for r s > 0.1 ? ] the table below gives values of nominal average output current for several preferre d values of current setting resistor (r s ) in the typical application circuit shown on page 1: r s ( ) nominal average output current (ma) 0.1 1000 0.13 760 0.15 667 the above values assume that the adj pin is floating and at a nominal voltage of v ref (=1.25v). note that r s = 0.1 ? is the minimum allowed value of sense resistor under these conditi ons 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 exte rnal 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 (100mv/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. ? gnd ZXLD1362 adj gnd + dc
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 19 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) 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 t he 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 controllin g 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 th e internal voltage reference as a pull-up resistor for the external transistor. driving the adj input from a microcontroller another possibility is to driv e the device from the open drain output of a mi crocontroller. 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 spike into adj input of the 1362 and cause erratic operation but the addition of a schottky clamp diode (cathode to adj) to ground and inclusion of a series resistor (3.3k) will prevent this. see the secti on on pwm dimming for more details of the various modes of control using high frequency and low frequency pwm signals. ? pwm gnd 0v v ad j gnd ZXLD1362 adj pwm gnd ZXLD1362 adj gnd gnd ZXLD1362 adj mcu 3.3k
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 20 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) shutdown mode taking the adj pin to a voltage below 0.2v for more than approxim ately 100s will turn off the output and supply current to a low standby level of 20a 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 cont rol voltage at the input of the comparator. adding capacitance increases this delay by appr oximately 0.2ms/nf. the graph below shows the variation of soft-start time for different values of capacitor. actual operating waveforms [v in =24v, r s =0.1 ? , l=68h, 22nf on adj] soft-start operation. output curr ent (ch2) and lx voltage (ch1) soft start time vs capacitance from adj pin to ground -2 0 2 4 6 8 10 12 14 16 0 20 40 60 80 100 120 capacitance (nf) soft start time (ms)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 21 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) vin capacitor selection a low esr capacitor should be used for input decoupling, as t he esr of this capacitor appears 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 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 inpu t 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 dielectric is recommended. capacitors with y5v dielectric are not suitable for decoupling in this application and should not be used. if higher voltages are used and the c in is 10 f. this can be an electrolytic capac itor provide a suitable 1mf ceramic capacitor is also used and positioned as close the v in of the ic as possible. a suitable capacitor would be nacew100m1006.3x8tr13f. the following web sites are useful when finding alternatives: www.murata.com www.niccomp.com www.kemet.com
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 22 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) inductor selection recommended inductor values for the ZXLD1362 are in the range 68 h to 220 h. higher values of inductance are recommended at higher supply volt ages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. higher va lues 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 t he peak output current and a c ontinuous current rating above the required mean output current. suitable coils for use with the zxld 1362 may be selected from t he mss range manufactured by coilcraft, or the npis range manufactured by nic components. the following websites may be useful in find ing suitable components. www.coilcraft.com www.niccomp.com www.wuerth-elektronik.de the inductor value should be chosen to maintain operating duty cy cle 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 ZXLD1362 case temperature below 60c. for detailed performance characteristics for the inductor values 68, 100, 150 and 220 h see graphs on pages 10-17. figure 3. ZXLD1362 minimum recommended inductor ? a luminium board, 2% a cc urac y , <60c casetem p er at ur e 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0 1020304050 60 supply v oltage ( v ) number of leds ZXLD1362 minimum recommended inducto r
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 23 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) diode selection for maximum efficiency and performance, the rectifier (d1) sh ould be a fast low capacitance schottky diode* with low reverse leakage at the maximum oper ating 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 abov e the peak coil current and a c ontinuous 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 t he 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 ripple, does not exceed the specified maximum value. *a suitable schottky diode would be 30bq100pbf (ir). reducing output ripple peak to peak ripple current in the led(s) can be reduced, if required, by shunting a capaci tor cled across the led(s) as shown below: ? v in v in i se nse lx ZXLD1362 r s l1 cled led d1 a value of 1 f will reduce the supply ripple current by a factor three (approx.). proportionally lower ripple can be achieved with higher capacitor values. note that the capacitor will not affect operating frequency or efficiency, but it will increase s tart- 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.
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 24 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) operation at low supply voltage below the under-voltage lockout threshold (vsd) the drive to t he output transistor is turned o ff to prevent device operation with excessive on-resistance of the output transistor. the output transistor is not full enh anced until the supply 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 zxld1360q. note that when driving loads of two or more leds, the forw ard 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 temperatures, 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. 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 us e of unsuitable coils, or excessiv e parasitic output capacitance o n the switch output. thermal compensation of output current high luminance leds often need to be supplied with a temperat ure compensated current in order to maintain stable and reliable operation at all drive levels. t he leds are usually mounted remotely from the device so, for this reason, the temperature coefficients of the internal circuits for the ZXLD1362 have been optimized to minimize the change in output current when no compensation is employed. if output current co mpensation is required, it is possible to use an external temperature sensing network - normally using negative temper ature coefficient (ntc) thermistors and/or diodes, mounted very close to the led(s). the output of the sensing networ k can be used to drive the adj pin in order to reduce output current with increasing temperature. m axi m u m power dissipation 0 100 200 300 400 500 600 700 800 900 1000 110 0 -50 -30 -10 10 30 50 70 90 110 130 150 ambient temperature (deg c) power ( m w)
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 25 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated application information (cont.) layout considerations lx pin the lx pin of the device is a fast switch ing node, so pcb tracks shou ld be kept as short as pos sible. 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 and the input decoupling capacitor as close to the device pins as possible to minimize parasitic resistance and inductance, which will degrade efficiency. 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 cathod e 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 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 filt ering for low frequency noise and provide protection against high voltage transients. high voltage tracks avoid running any high voltage tracks close to the adj pi n, 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 ZXLD1362 evaluation boards are available on request. these boar ds contain leds to allow quick testing of the 1362 device. additional terminals allow for interfacing to customers own led products. gnd ZXLD1362 adj 3.3k 100nf gnd
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 26 of 28 www.diodes.com december 2010 ? diodes incorporated 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 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 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 current i outavg 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 = 0.1d pwm /r s [for d pwm >0.001] this mode is preferable if optimum led 'whiteness' is re quired. it will also provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expense of greater output ripple.
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 27 of 28 www.diodes.com december 2010 ? diodes incorporated a product line o f diodes incorporated ordering information device part mark package code packaging (note 4) reel size (mm) reel width (mm) quantity per reel part number suffix aec-q100 grade ZXLD1362et5ta 1362 et5 tsot23-5 180 8 3000 ta 1 package outline dimensions tsot23-5
ZXLD1362 ZXLD1362 document number: ds33472 rev. 2 - 2 28 of 28 www.diodes.com december 2010 ? 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 described herein. diodes incorporated does not assume any liability arising out of the application or use of this document or any product described her ein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or us er of this document or products described herein in such applica tions shall assume all risks of such use and will agree to hold diodes in corporated 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 what soever in respect of any pr oducts purchased through unauthoriz ed sales channel. should customers purchase or use diodes in corporated products for any unintended or unauthorized application, customers shall i ndemnify and hold diodes incorporated and its representatives harmless a gainst all claims, damages, expens es, 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 prop erly 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-cri tical, life support devices or systems, notwithstanding any devic es- or systems- related information or support that may be provided by diodes inco rporated. further, customers must fully indemnify diodes inc orporated and its representatives against any damages aris ing out of the use of diodes incorporated products in such safety-critical, life su pport devices or systems. copyright ? 2010, diodes incorporated www.diodes.com

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