1 fn7371.1 EL7630 white led b oost regulator the EL7630 represents a high efficiency, constant frequency pwm regulator for use in white led driving applications. with efficiencies up to 86%, the EL7630 operates at 1.35mhz switching frequency while operating from an input voltage of between 2.7v and 5.5v. the maximum output voltage of 27v enables the EL7630 to drive up to 6 leds in series. it is also possible to use the EL7630 to drive leds in series/parallel combination for applications requiring up to 15 leds. available in the 6 ld sc-70 and the 5 ld tsot packages, the EL7630 features the same pino ut as competitive products but offers higher efficiency, constant frequency operation. it is specified for operation over the -40c to +85c ambient temperature range. pinouts EL7630 (6 ld sc-70) top view EL7630 (5 ld tsot) top view features ? up to 6 leds in series ? 27v maximum output ? 2.7v to 5.5v input ? up to 86% efficient ? 1.35mhz constant frequency ? enable/pwm dimming control ? pb-free plus anneal available (rohs compliant) applications ? led backlighting ? cell phones ?pdas ? handheld devices 1 2 3 6 4 lx gnd fb vin enab 5pgnd 1 2 3 5 4 lx gnd fb vin enab ordering information part number (see note) part marking tape & reel package (pb-free) pkg. dwg. # EL7630icz-t7 bca 7? (3k pcs) 6 ld sc-70 p6.049 EL7630icz-t7a bca 7? (250 pcs) 6 ld sc-70 p6.049 EL7630iwtz-t7 baac 7? (3k pcs) 5 ld tsot mdp0049 EL7630iwtz-t7a baac 7? (250 pcs) 5 ld tsot mdp0049 note: intersil pb-free plus anneal pr oducts employ special pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are rohs compliant and compatible with both snpb and pb-free soldering operations. intersil pb-free products are msl classified at pb-free peak reflow temperatures that meet or exceed the pb-free requirements of ipc/jedec j std-020. data sheet february 22, 2006 caution: these devices are sensitive to electrosta tic discharge; follow proper ic handling procedures. 1-888-intersil or 1-888-468-3774 | intersil (and design) is a registered trademark of intersil americas inc. copyright intersil americas inc. 2006. all rights reserved all other trademarks mentioned are the property of their respective owners. n o t r e c o m m e n d e d f o r n e w d e s i g n s r e c o m m e n d e d r e p l a c e m e n t p a r t i s l 9 7 6 3 4
2 february 22, 2006 absolute maxi mum ratings (t a = 25c) input voltage (v in ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +6v lx voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +27v fb voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +6v enab voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +6v pgnd to gnd (sc-70 package) . . . . . . . . . . . . . . . . -0.3v to +0.3v operating temperature . . . . . . . . . . . . . . . . . . . . . . .-40c to +85c maximum junction temperature . . . . . . . . . . . . . . . . . . . . . . +125c storage temperature . . . . . . . . . . . . . . . . . . . . . . . .-65c to +150c lead temperature (soldering, 10s) . . . . . . . . . . . . . . . . . . . . +300c caution: stresses above those listed in ?absolute maximum ratings? may cause permanent damage to the device. this is a stress o nly rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. important note: all parameters having min/ max specifications are guaranteed. typ values are for information purposes only. unle ss otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: t j = t c = t a electrical specifications v in = 3v, v enab = 3v, over temperature from -40 c to 85c unless otherwise specified. parameter description condition min typ max unit v in-min minimum operating voltage v out = 16v, i led = 20ma 2.7 v v in-max maximum operating voltage v out = 25v, i led = 20ma 5.5 v v fb feedback voltage t a = 25c 86 95 104 mv 80 95 115 mv i fb fb pin bias current 100 na i in supply current enab = 3v, output not switching 0.6 1.0 ma enab = 0v 1 a f osc switching frequency t a = 25c 0.8 1.35 1.8 mhz 0.8 1.35 1.9 mhz d max maximum duty cycle t a = 25c 85 90 % 82 90 % i lim switch current limit t a = 25c 280 350 ma 250 350 ma r ds(on) switch on resistance i lx = 100ma 750 m ? i leak switch leakage current v lx = 27v 0.01 1 a v enab-hi enab voltage high 2.5 v v enab-lo enab voltage low 0.6 v i enab enab pin bias current 1a ? i led / ? v in line regulation v in = 2.7v to 5v 0.2 %/v EL7630
3 february 22, 2006 typical application figure 1. typical application circuit and efficiency vs led current c1 vdd lx gnd l1 22h d1 c2 0.22f r set 4.75 ? 2.7v~5.5v off/on leds EL7630 1f enab fb v in efficiency (%) 65 70 75 80 85 90 0 5 10 15 20 25 30 led current (ma) typical performance curves figure 2. quiescent current (enable) figure 3. load regulation (v in =4v) figure 4. line regulation figure 5. switching frequency vs temperature 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0123456 v in (v) quiescent current (ma) 24.56 24.565 24.57 24.575 24.58 24.585 24.59 24.595 24.6 0 5 10 15 20 v out (v) led current (ma) 24.56 24.58 24.6 24.62 24.64 24.66 24.68 24.7 2.5 3 3.5 4 4.5 5 5.5 v in (v) led current (ma) 1.2 1.22 1.24 1.26 1.28 1.3 1.32 1.34 -40 10 60 temperature (c) switching frequency (mhz) EL7630
4 february 22, 2006 block diagram pin functions lx (pin 1) - switching pin. connect to inductor and diode. gnd (pin 2) - ground pin. connect to local ground. fb (pin 3) - feedback pin. connect to the cathode of lowest led and the sense resistor. enab (pin 4) - enable pin. connect to enable signal to turn-on or off the device. pgnd (pin 5, sc-70 package) - ground pin. connect to pin 2 and to local ground. v in (pin5/pin6 sc-70 package) - input supply pin. connect to the input supply voltage. figure 6. pwm dimming curve (400hz) typical performance curves 0 4 8 12 16 20 0 20 40 60 80 100 duty-cycle (d) i out (ma) 22 fet driver pwm logic controller current sense gm amplifier 1.2mhz oscillator and ramp generator bandgap reference generator 95mv gm amp compensation pwm comparator vin enable lx pgnd fb (shared with pgnd in tsot5 package) gnd EL7630 fet driver pwm logic controller current sense gm amplifier 1.2mhz oscillator and ramp generator bandgap reference generator 95mv gm amp compensation pwm comparator vin enable lx pgnd fb (shared with pgnd in tsot5 package) gnd EL7630 figure 7. EL7630 block diagram EL7630
5 february 22, 2006 detailed description EL7630 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. it can drive up to 6 leds in series or 15 leds in parallel/series configuration, with efficiencies of up 86%. EL7630 operates from an input voltage of 2.7v to 5.5v and can boost up to 27v. steady-state operation EL7630 operates with constant frequency pwm. the switching frequency is around 1.2mhz. depending on the input voltage, inductance, number of leds and the led current, the converter operates in either continuous conduction mode or discontinuous conduction mode. both are normal. the forward current of the led is set using the r set resistor. in steady state mo de, this current is given by the equation: shut-down the enab pin, when taken low places EL7630 into power down mode. when in power down, the supply current reduced to less than 1a. dimming control the enab pin also doubles as a brightness control. there are two different types of dimming control methods. the first dimming control is controlled through the duty-cycle of the enab input pwm waveform, which can operate at frequencies of 400hz to 1khz. the leds operate at either zero or full current. this is called pwm dimming control method. the relationship between the average led current and the duty-cycle (d) of the enab pin?s waveform is as follows: the magnitude of the pwm signal should be higher than the minimum enab voltage high. the bench pwm dimming test results are shown in figure 8. in the test, two pwm frequencies 400hz and 1khz are chosen to compare the linear dimming range. it is clear that for lower pwm frequency, the linear dimming range is wider than one for higher pwm frequency. in the pwm dimming test, the output capacitor is 0.22f. the second dimming control is to apply a variable dc voltage to adjust the led current. this is called analog dimming control. the dimming c ontrol using a dc voltage is shown in figure 9. as the dc dimming signal voltage increases, the voltages drop on r 1 and r 2 increases and the voltage drop on r set decreases. thus, the led current decreases. the dc dimming signal voltage can be a variable dc voltage or a dc voltage generated from a pwm control signal. for some application areas, the pwm control signal is a high frequency signal. to make dimming controllable with these high frequency pwm signals, the high frequency components of the pwm control signal should be filtered to get the equivalent dc voltage. the equivalent dc voltage is then used as the variable dc voltage for dimming led current. where f is the brightness with respect to the undimmed value. i led v fb r set --------------- = (eq. 1) average i led v fb r set --------------- d ? = (eq. 2) 0 5 10 15 20 25 0 10203040506070809010 duty-cycle (%) i out (ma) figure 8. pwm dimming linear range (for 400hz and 1khz pwm frequencies condition, c out = 0.22f) 1khz 400hz i led v fb r set --------------- r 1 r 2 + r 2 -------------------- - v dim r 1 ? r set r 2 ? --------------------------- ? ? = (eq. 3) v dim r 2 r 1 ------ - v fb 1 r 1 r 2 ------ - f ? + ?? ?? ?? ?? = (eq. 4) EL7630
6 february 22, 2006 for a required led current i led and chosen values of r 1 and r 2 , the dimming dc voltage v dim can be expressed as: it is clear that as the required led current i led is closed to the rate current v fb /r set , v dim is closed to v fb . as the required led current is lowe r than the rate current, the dimming dc voltage v dim is increased in r 2 /r 1 factor. open-voltage protection in some applications, it is possible that the output is opened, e.g. when the leds are disconnected from the circuit or the leds fail. in this case the feedback voltage will be zero. the EL7630 will then switch to a high duty cycle resulting in a high output voltage, which may cause the lx pin voltage to exceed its maximum 27v rating. to implement overvoltage protec tion, a zener diode dz and a resistor r 1 can be used at the output and fb pin to limit the voltage on the lx pin as shown in figure 10. it is clear that as the zener is turned on, due to the overvoltage, the zener diode?s current will set up a voltage on r 1 and r set and this voltage is applied on fb pin as the feedback node. this feedback will prevent the output from reaching the overvoltage condition. in the overvoltage protection circuit design, the zener voltage should be larger than the maximum forward voltage of the led string. components selection the input capacitance is normally 0.22f~4.7f and the output capacitor is 0.22f~1f. x5r or x7r type of ceramic capacitor with the correct voltage rating is recommended. the output capacitor value will affect pwm dimming performance. for lower output capacitor values, the range of pwm dimming is wider than for higher values of output capacitor. when choosing an inductor, make sure the inductor can handle the average and peak currents given by the following formulas (80% efficiency assumed): where: ? ? i l is the peak-to-peak inductor current ripple in ampere ? l inductance in h. ?f osc switching frequency, typically 1.2mhz the boost inductor can be chosen in a wide range of inductance (10h~82h). for 10h inductor value, the boost inductor current will be in discontinuous mode. as the inductor value decreases further, the ripple of the boost inductor current is increased and can even trigger overcurrent protection. for high boost inductor value, the boost inductor current will be in continuous mode. for general boost converter, as the converter operates in continuous mode, there is right half plane zero (rhpz). if rhpz frequency is less than or close to the control loop crossover frequency, there is a stability issue. in EL7630, the compensation network is well designed and there is no rhpz stability issue even if the inductor value is over 82h. for the same series of inductors, a lower inductance has lower dc resistance (dcr), which causes less conducting loss, but higher peak to p eak current variation, which generates more rms current loss. figure 11 shows the efficiency of the demo board with different led load for a specific series of inductor. the diode used should be a schottky type with minimum reverse voltage of 28v. the diode?s peak current is the same as the inductor?s peak current. the schottky rms current is: EL7630 c1 vdd lx enab fb gnd l1 22h d1 c2 0.22f r set 4.75 ? off/on leds 1f lx v in 2.7v~5.5v r1 r2 dimming signal figure 9. analog dimming control application circuit v dim v fb v fb i led ? r set ? ?? + r 2 r 1 ------ - ? = (eq. 5) EL7630 c1 l1 22h d1 c2 0.22f r set 4.75 ? 2.7v~5.5v off/on leds 1f vdd lx enab fb gnd v in r1 dz figure 10. led driver with overvoltage protection circuit i lavg i led v out ? 0.8 v in ? --------------------------------- = (eq. 6) i lpk i lavg 1 2 -- - i l ? ? + = (eq. 7) i l ? v in v out v in ? ?? ? lv out f osc ?? -------------------------------------------------- - = (eq. 8) i rms d2i lavg 2 ? 1 6 -- - i l 2 ? ? + ?? ?? ? = (eq. 9) EL7630
7 all intersil u.s. products are manufactured, asse mbled and tested utilizing iso9000 quality systems. intersil corporation?s quality certifications ca n be viewed at www.intersil.com/design/quality intersil products are sold by description only. intersil corpor ation reserves the right to make changes in circuit design, soft ware and/or specifications at any time without notice. accordingly, the reader is cautioned to verify that data sheets are current before placing orders. information furnishe d by intersil is believed to be accurate and reliable. however, no responsibility is assumed by intersil or its subsidiaries for its use; nor for any infringements of paten ts or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of intersil or its subsidiari es. for information regarding intersil corporation and its products, see www.intersil.com february 22, 2006 the efficiency bench test result s are shown in figure 11. in the test, the input voltage is 4v and 2, 3, 4, 5 and 6 leds are used as the load (boost inductor l = 22h sumida cdrh5d28r-220nc). white led connections one leg of leds connected in series will ensure brightness uniformity. the 27v maximum output voltage specification enables up to 6 leds to be placed in series. in order to output more power to drive more leds, leds should be in series/parallel connection. due to the led's negative temperature coefficient, in each parallel branch, the driving source should be high impedance, to balance the led current in each branch. one of the ways to ensure the brightness uniformity is to add mirror current balance circuit, built up with three transistors for the 15 leds series/parallel connection application shown in figure 12. pcb layout considerations the pcb layout is very important for the converter to function properly. for the sc-70 6 pin package, power ground and signal ground should be separated to ensure the high pulse current in the power ground does not interfere with the sensitive signals conn ected to signal ground. both grounds should only be connecte d at one point right at the chip. the heavy current loops (v in -l1-lx-pgnd, and v in - l1-d1-c2-pgnd) should be as short as possible. for the tsot 5 pin package, there is no separated gnd. all return gnds should be connected in gnd pin but with no sharing branch. based on the signal level on each branch, the lower power level of the branch, the closer the branch to gnd pin in order to minimize the branch interactive. the fb pin is most important. the current sense resistor r set should be very close to this pin. if a long trace is required to the leds, a small decoupling capacitor should be placed at this pin. the heat of the ic is mainly dissipated through the pgnd pin. maximizing the copper area connected to this pin is preferable. in addition, a solid ground plane is always helpful for the emi performance. the demo board is a good example of layout based on the principle. please refer to the EL7630 application brief for the layout. figure 11. efficiency curve with 2, 3, 4, 5 and 6 leds load 55 60 65 70 75 80 85 90 0102030 led current (ma) 22h,v in =4v 3led 4led 5led 2led 6led efficiency (%) EL7630 c1 vdd lx enab fb gnd l1 d1 c2 r set v in 2.7v~5.5v off/on leds EL7630 vdd lx enab fb gnd l1 d1 figure 12. leds in series/parallel with mirror current balance EL7630
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