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zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 1 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated high accuracy 1a, 60v led driver with internal switch description the zxld1366 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected leds efficiently from a voltage source higher than the led voltage. the dev ice operates from an input supply between 6v and 60v and provides an externally adjustable output current of up to 1a. depending upon supply voltage and external components, this can provide up to 48 watts of output power. the zxld1366 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. output current can be adjust ed above, or below the set value, by applying an external control signal to the 'adj' pin. the adj pin will accept either a dc voltage or a pwm waveform. depending upon the control frequency, this will provide either a continuous (dimmed) or a gated output current. soft-start can be forced using an external capacitor from the adj pin to ground. applying a voltage of 0.2v or lower to the adj pin turns the output off and switches the device into a low current standby state. pin assignments typical application circuit features ? typically better than 0.8% output current accuracy ? available in thermally enhanced dfn package ? simple and with low part count ? single pin on/off and brightness control using dc voltage or pwm ? pwm resolution up to 1000:1 ? high efficiency (up to 97%) ? wide input voltage range: 6v to 60v ? inherent open-circuit led protection applications ? low voltage halogen replacement leds ? automotive lighting ? low voltage industrial lighting ? led back-up lighting ? illuminated signs ? emergency lighting ? selv lighting ? lcd tv backlighting ? refrigeration lights . (top view) tsot23-5 i sense v in 2 1 3 4 5 adj gnd lx 1 2 3 4 5 6 dfn3030-6 (top view) lx gnd adj v in i sense gnd (top view) so-8-ep 4 6 5 1 7 2 8 3 lx gnd gnd adj v in gnd gnd i sense v in i sense lx gnd zxld1366 adj v in (24v) rs 0.2v 4.7mf c1 gnd 100nf d1 l1
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 2 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated block diagram figure 1 pin connection for tsot23-5 package pin description name tsot23-5 dfn3030-6 so8-ep description 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 br ightness control pin: ? leave floating for normal operation.(v adj = v ref = 1.25v giving nominal average output current i outnom = 0.2v/r s ) ? drive to voltage below 0.2v to turn off output current ? drive with dc voltage (0.3v < v adj < 2.5v) to adjust output current from 25% to 200% of i outnom ? connect a capacitor from this pin to ground to set soft-start time. soft start time increases approximately 0.2ms/nf i sense 4 4 5 connect resistor r s from this pin to v in to define nominal average output current i out nom = 0.2v/r s (note : r smin = 0.2v 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 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
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 3 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated absolute maximum ratings (voltages to gnd unless otherwise stated) symbol paramete r 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 volt age -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 26) sot23-5; 1 dfn; 1.8 w t op operating temperature -40 to 125 c 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. thermal resistance symbol parameter rating unit tsot23-5 so-8-ep dfn3030-6 j a junction to ambient 82 45 44 c/w jb junction to board 33 - - jc junction to case - 7 14 electrical characteristics (test conditions: v in = 24v, t amb = 25c, unless otherwise specified.) (a) symbol paramete r condition min. typ. max. unit v in input voltage see note (b) 6 60 v su internal regulator start-up threshold 4.85 5.2 v v sd internal regulator shutdown threshold 4.4 4.75 v i inqof f quiescent supply current with output off a dj pin grounded 65 108 a i inqon quiescent supply current with output switching (c) a dj pin floating, l=68mh, 3 leds, f=260khz 1.6 ma v sense mean current sense threshold voltage (defines led current setting accuracy) measured on i sense pin w ith 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 refe rence voltage measured on adj pin w ith pin floating 1.25 v dv ref /dt temperature coefficient of v ref 50 ppm/ c v adj external control voltage range on adj pin f or dc brightness control (d) 0.3 2.5 v v adjoff dc voltage on adj pin to switch device from active (on) state to quiescent (off) state v adj falling 0.15 0.2 0.27 v notes: (a) production testing of the device is per formed at 25c. functional operation of the device and parameters specified over a - 40c to +105c temperature range, are guaranteed by design, characterization and process control. (b) v in > 16v to fully enhance output transistor. otherwise out current must be derated - see graphs. operation at low supply may caus e excessive heating due to increased on-resist ance. tested at 7v guaranteed for 6v by design. (c) static current of device is approximately 700 ma, see graph, page 17 (d) 100% brightness corresponds to v adj = v adj (nom) = v ref . driving the adj pin above v ref will increase the v sense . threshold and output current proportionally
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 4 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated electrical characteristics (test conditions: v in = 24v, t amb = 25c, unless otherwise specified.) (a) (cont.) symbol paramete r condition min. typ. max. unit v adjon dc voltage on adj pin to switch device f rom 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 lx = 1a 0.5 0.75 ? i lx ( leak ) lx switch leakage current 5 a d pwm(lf) duty cycle range of pwm signal applied to a dj 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 see note (*) 5:1 t ss soft start time t ime taken for output current to reach 90% of f inal value after voltage on a dj 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) a dj pin floating l=68mh (0.2v) i out =1a @ v led =3.6v driving 3 leds 260 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 f lxmax recommended maximum operating f requency 500 khz d lx recommended duty cycle range of output switch at f lxmax 0.3 0.7 notes: (*) ratio of maximum brightness to minimum brightness be fore shutdown vref = 1.25/0.3. vr ef externally driven to 2.5v, ratio 10:1. (?) parameters are not tested at production. parameters are guaranteed by design, characterization and process control.
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 5 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated device description the device, in conjunction with the coil (l1) and current sense resistor (r s ), forms a self-oscillating continuous-mode buck converter. device operation (refer to figure 1 - block diagram and figure 2 operating waveforms) operation can be best understood by assuming that the adj pin of the device is unconnected and the voltage on this pin (v adj ) appears directly at the (+) input of the comparator. when input voltage v in is first applied, the initial current in l1 and r s is zero and there is no output from the current sense circuit. under this condition, the (-) input to the comparator is at 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 vo ltage at the (-) input of the comparator. when this r eaches the thres hold 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 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 produc e 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 r epeats, with the comparator input ramping between limits of v adj 15%. switching thresholds with v adj = v ref , the ratios of r1, r2 and r3 define an average v sense switching threshold of 200mv (measured on the i sense pin with respect to v in ). the average output current i outnom is then defined by this voltage and r s according to: i outnom = 200mv/r s nominal ripple current is 30mv/r s adjusting output current the device contains a low pass filter between the adj pin and the threshold comparator and an internal current limiting resistor (50k ? nom) between adj and the internal reference voltage. 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.
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 6 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated figure 2 theoretical 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
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 7 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated actual operating waveforms [v in =15v, r s =0.2v, l=68h] normal operation. output current (ch3) and lx voltage (ch2) actual operating waveforms [v in =30v, r s =0.2v, l=68h] normal operation. output current (ch3) and lx voltage (ch2) actual operating waveforms [v in =60v, r s =0.2v, l=68h] normal operation. output current (ch3) and lx voltage (ch2)
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 8 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions zxld1366 output current l=68 h 0.980 1.000 1.020 1.040 1.060 1.080 1.100 01 02 03 04 05 06 0 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 1 02 03 04 05 06 0 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=68h zxld1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0 1 02 03 04 05 06 0 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=68h
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 9 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 switching frequency l=68h 0 50 100 150 200 250 300 350 400 450 500 0 102030405060 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 duty cycle l=68h 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 1 02 03 04 05 06 0 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 10 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 output current 0.960 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0 102030405060 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0 1 02 03 04 05 06 0 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 1 02 03 04 05 06 0 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=100h l=100h l=100h
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 11 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 switching frequency l=100h 0 50 100 150 200 250 300 350 400 450 500 0 1 02 03 04 05 06 0 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 duty cycle l=100h 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 1 02 03 04 05 06 0 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 12 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 output current l=150h 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0 102030405060 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0 1 02 03 04 05 06 0 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 102030405060 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=150h l=150h
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 13 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 switching frequency l=150h 0 50 100 150 200 250 300 350 400 450 500 0 1 02 03 04 05 06 0 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 duty cycle l=150h 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 1 02 03 04 05 06 0 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 14 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 output current 0.980 1.000 1.020 1.040 1.060 1.080 1.100 0 1 02 03 04 05 06 0 supply voltage (v) output current (a) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 output current deviation -10% -8% -6% -4% -2% 0% 2% 4% 6% 8% 10% 0 1 02 03 04 05 06 0 supply voltage (v) output current deviation (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds zxld1366 efficiency 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% 0 1 02 03 04 05 06 0 supply voltage (v) efficiency (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=220h l=220h l=220h
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 15 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) zxld1366 switching frequency l=220h 0 50 100 150 200 250 300 350 400 450 500 0 1 02 03 04 05 06 0 supply voltage (v) switching frequency (khz) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 102030405060 supply voltage (v) duty cycle (%) 01 leds 03 leds 05 leds 07 leds 09 leds 11 leds 13 leds 15 leds l=220h zxld1366 duty cycle
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 16 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated typical operating conditions (cont.) led current vs v ad j 0 200 400 600 800 1000 1200 0123 adj pin voltage (v) led current (ma) r=200m ? r=300m ? r=680m ? vref 1.238 1.2385 1.239 1.2395 1.24 1.2405 1.241 1.2415 1.242 1.2425 1.243 0 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) output transistor fully enhanced output transistor not fully enhanced
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 17 of 32 www.diodes.com june 2010 ? diodes incorporated 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 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
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 18 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated application information setting nominal average output current with external resistor rs the nominal average output current in the led(s) is determined by the value of the external current sense resistor (rs) connected between vin and isense and is given by: i outnom = 0.2/r s [for r s 0.2 v ] the table below gives values of nominal average output current for several prefe rred values of current setting resistor (r s ) in the typical application circuit shown on page 1: r s (v) 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 = 0.2v 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 ex ternal 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. gnd zxld1366 adj gnd + dc
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 19 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated output current adjustment by pwm control directly driving adj input a pulse width modulated (pwm) signal with duty cycle dpwm 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 zxld1366 and cause erratic operation but the addition of a schottky clamp diode (eg diodes inc. sd103cws) to ground and inclusion of a series resistor (3.3 k) 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. pw m gnd 0v v adj gnd zxld1366 adj pwm gnd zxld1366 adj gnd gnd zxld1366 adj mcu 3.3k
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 20 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated 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 vref 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 [vin=60v, rs=0.2 v , 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. 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)
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 21 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated 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. when higher voltages are used with the c in = 10 f, an electrolytic capacitor can be used provided that a suitable 1mf ceramic capacitor is also used and positioned as close to the v in pin as possible. a suitable capacitor would be nacew100m1006.3x8tr13f (nic components). the following web sites are useful when finding alternatives: www.murata.com www.niccomp.com www.kemet.com
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 22 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated 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 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 vin 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 1366 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 zxld1366 case temperature below 60c. for detailed performance characteristics for the inductor values 68, 100, 150 and 220 h see graphs on pages 10-17. 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 (tsot23-5)
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 23 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated figure 4 zxld1366 minimum recommended inductor (dfn3030-6) figure 5 zxld1366 minimum recommended inductor (so-8-ep) zxld1366q so-8-ep minimum recommended inductor 2% accuracy, <60c case temperature, 1a target current 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 1 2 3 4 5 6 7 8 9 10 11 12 number of leds . supply voltage (v) legend 47h 68h 100h 150h 220h
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 24 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated 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 b3100 (diodes inc). 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: figure 6 reduce output ripple a value of 1mf will reduce the supply ripple current by a fa ctor 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. v in v in i sense lx zxld1366 rs l1 cled led d1
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 25 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated operation at low supply voltage below the under-voltage lockout threshold (v sd ) the drive to the output transistor is turned off to prevent device operation with excessive on-resistance of the output transistor. the output transistor is not full 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. 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 25mm2 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.
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 26 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated in order to maximize the thermal capabilities of the dfn3030-6 and the so-8-ep packages thermal vias should be incorporated into the pcb. see figures 7 and 8 fo r examples used in the zxld1366 evaluation boards. figure 7 suggested layout for dfn3030-6 package figure 8 suggested layout for so-8-ep package vias ensure an effective path to the ground plane for the heat flow therefore reducing the thermal impedance between junction and ambient temperature. diodes came to the conclusi on 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 tsot23-5 package guaranteeing an effective thermal path.
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 27 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated 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 zxld1366 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 temperat ure 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. 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 catho de 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. gnd zxld1366 adj 3.3k 100nf gnd
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 28 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated evaluation pcb zxld1366 evaluation boards are available on reques t. terminals allow for interfacing to customers own led products. 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 0.2d pwm /r s [for d pwm >0.001] this mode is preferable if optimum led 'whiteness' is requ ired. it will also provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expense of greater output ripple. v adj pwm voltage to n ioutavg 0v 0 to ff 0.2/rs ioutnom output current
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 29 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated ordering information device package reel size (inches) reel width (mm) quantity per reel device mark zxld1366et5ta tsot23-5 7? 8 3000 1366 zxld1366dactc dfn3030-6 13? 12 3000 1366 zxld1366en8tc so-8-ep 13? 12 2500 1366 package outline dimensions tsot23-5 dim. millimeters inches dim. millimeters inches min. max. min. max. min. max. min. max. a - 1.00 - 0.0393 e1 1.60 bsc 0.062 bsc a1 0.01 0.10 0.0003 0.0039 e 0.95 bsc 0.037 bsc a2 0.84 0.90 0.0330 0.0354 1.90 bsc 0.074 bsc b 0.30 0.45 0.0118 0.0177 l 0.10 0.60 0.0039 0.0236 c 0.12 0.20 0.0047 0.0078 l2 0.25 bsc 0.010 bsc d 2.90 bsc 0.114 bsc q 4 12 4 12 e 2.80 bsc 0.110 bsc
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 30 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated package outline dimensions dfn3030-6 dim millimeters inches dim millimeters inches min. max. min. max. min. max. min. max. a 0.700 0.800 0.0275 0.0315 d2 1.950 2.050 0.0768 0.0807 a1 0.000 0.050 0.000 0.00197 e 0.950 bsc 0.0374 bsc a3 0.203 ref 0.008 e 2.950 3.050 0.116 0.120 b 0.300 0.400 0.0118 0.0157 e2 1.150 1.250 0.0452 0.0492 d 2.950 3.050 0.116 0.120 e1 1.900ref 0.0748 l 0.450 0.550 0.0177 0.0216 top view bottom view pin 1 dot by marking side view chamfer 0.300x45 pin #1 identification d a a3 a1 b d2 e e e2 e1 l
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 31 of 32 www.diodes.com june 2010 ? diodes incorporated a product line o f diodes incorporated package outline dimensions so-8-ep
zxld1366 zxld1366 document number: ds31992 rev. 5 - 2 32 of 32 www.diodes.com june 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 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 ? 2010, diodes incorporated www.diodes.com

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