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june 2012 ? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev.1.0.1 FAN5346 ? series boost led driver with pwm dimming interface FAN5346 series boost led driver with pwm dimming interface features ? asynchronous boost converter ? drives leds in series: ? FAN5346s20x: 20v output ? FAN5346s30x: 30v output ? 2.5v to 5.5v input voltage range ? pwm dimming for led brightness control ? 5khz to 100khz pwm dimming frequency range ? 1.2mhz fixed switching frequency ? soft-start capability ? input under-voltage lockout (uvlo) ? output over-voltage protection (ovp) ? short-circuit detection ? thermal shutdown (tsd) protection ? small form-factor 6-lead ssot23 package applications ? cellular mobile handsets ? mobile internet devices ? portable media players ? pda, dsc, mp3 players description the FAN5346 is an asynchronous constant-current led driver that drives leds in series to ensure equal brightness for all the leds. FAN5346s20x has an output voltage of 20v and can drive up to 5 leds in series. FAN5346s30x has an output voltage of 30v and up to 8 leds in series. optimized for small form-facto r applications, the 1.2mhz fixed switching frequency allows the use of small inductors and capacitors. the FAN5346 uses a pwm dimming control interface to set the brightness levels of the le ds. a pwm signal of 5khz to 100khz is applied to the en pin. for safety, the device features integrated over-voltage, over- current, short-circuit detection, and thermal-shutdown protections. in addition, input under-voltage lockout protection is triggered if the battery voltage is too low. the FAN5346 is available in a 6-lead ssot23 package. it is ?green? and ro hs compliant. (please see http://www.fairchildsemi.com/c ompany/green/index.html for fairchild?s definition of green). ordering information part number output voltage option temperature range package FAN5346s20x 20v -40 to 85c 6-lead, supersot?-6, jedec mo-193, 1.6mm wide (ma06a) FAN5346s30x 30v .
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 2 FAN5346 ? series boost led driver with pwm dimming interface typical application diagram figure 1. typical application block diagram figure 2. functional block diagram
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 3 FAN5346 ? series boost led driver with pwm dimming interface pin configuration figure 3. pin assignments, top view pin definitions pin # name description 5 vout boost output voltage . output of the boost regulator. connect the leds to this pin. connect c out (output capacitor) to gnd. 1 vin input voltage . connect to the power source and decouple with c in to gnd. 4 en enable brightness control . program dimming levels by driving pin with the pwm signal. 3 fb voltage feedback . the boost regulator regulates this pin to 0.250v to control the led string current. tie this pin to a current setting resistor (r set ) between gnd and the cathod e of the led string. 6 sw switching node . tie inductor l1 from vin to sw pin. 2 gnd ground . tie directly to a gnd plane.
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 4 FAN5346 ? series boost led driver with pwm dimming interface absolute maximum ratings stresses exceeding the absolute maximum ratings may damage t he device. the device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. in addition, extended exposure to stresses above the recommended operati ng conditions may affect device reliability. the absolute maximum ratings are stress ratings only. symbol parameter min. max. unit v in vin pin -0.3 6.0 v v fb , v en fb, en pins -0.3 v in + 0.3 v v sw sw pin FAN5346s20x -0.3 22.0 v FAN5346s30x -0.3 33.0 v v out vout pin FAN5346s20x -0.3 22.0 v FAN5346s30x -0.3 33.0 v esd electrostatic discharge protection human body model per jesd22-a114 1.5 kv charged device model per jesd22-c101 1.5 t j junction temperature -40 +150 c t stg storage temperature -65 +150 c t l lead soldering temperature, 10 seconds +260 c recommended operating conditions the recommended operating conditions table defines the conditi ons for actual device operation. recommended operating conditions are specified to ensure optimal performance to the datasheet specif ications. fairchild does not recommend exceeding them or designing to absolute maximum ratings. symbol parameter min. max. unit v in v in supply voltage 2.5 5.5 v v out v out voltage (1) FAN5346s20x 6.2 18.5 v FAN5346s30x 6.2 28.5 i out v out load current 5 25 ma t a ambient temperature -40 +85 c t j junction temperature -40 +125 c note: 1. application should guarantee that minimum and maximum du ty cycle fall between 20-85% to meet the specified range. thermal properties junction-to-ambient thermal resistance is a function of application and board layout. this data is measured with four-layer 2s2p boards in accordance to jedec standard jesd51. specia l attention must be paid not to exceed junction temperature t j(max) at a given ambient temperature t a . symbol parameter typical unit ja junction-to-ambient thermal resistance, ssot23-6 package 151 c/w
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 5 FAN5346 ? series boost led driver with pwm dimming interface electrical specifications v in = 2.5v to 5.5v and t a = -40c to +85c unless otherwise noted. typical values are at t a = +25c and v in = 3.6v. symbol parameter conditions min. typ. max. unit power supplies i sd shutdown supply current en = gnd 0.30 0.90 a i q(active) quiescent current at i load = 0ma device not switch ing, no load 300 a v uvlo under-voltage lockout threshold v in rising 2.10 2.35 2.60 v v in falling 1.80 2.05 2.30 v uvhyst under-voltage lockout hysteresis 250 mv en: enable pin v ih high-level input voltage 1.2 v v il low-level input voltage 0.4 v r en en pull-down resistance 200 300 400 k f pwm pwm dimming frequency (3) 5 100 khz t sd en low, shutdown pulse width v in = 3.6v; from falling edge of en 1 ms feedback and reference v fb feedback voltage i led = 20ma from -40c to +85c, 2.5v v in 5.5v 230 250 270 mv i fb feedback input current v fb = 250mv 0.1 1.0 a power outputs r ds(on)_q1 boost switch on resistance v in = 3.6v, i sw = 100ma 600 m v in = 2.5v, i sw = 100ma 650 i sw(off) sw node leakage (2) en = 0, v in = v sw = v out = 5.5v, v led = 0v 0.1 2.0 a i lim-pk boost switch peak current limit FAN5346s20x: v in = 3.2v to 4.3v, t a =-20c to +60c, v f = 3.4v, 4 leds 200 300 400 ma FAN5346s30x 500 750 1000 oscillator f sw boost regulator switching frequency 0.95 1.15 1.35 mhz output and protection v ovp boost output over-voltage protection FAN5346s20x 18.0 20.0 21.5 v FAN5346s30x 27.5 30.0 32.5 ovp hysteresis FAN5346s20x 0.8 FAN5346s30x 1.0 v tlsc v out short-circuit detection threshold v out falling v in ? 1.4 v v thsc v out short-circuit detection threshold v out rising v in ? 1.2 v d max maximum boost duty cycle (3,4) 85 % d min minimum boost duty cycle (3,4) 20 t tsd thermal shutdown 150 c t hys thermal shutdown hysteresis 35 c notes: 2. sw leakage current includes the leakage current of two internal switches; sw to gnd and sw to v out . 3. not tested in production; guaranteed by design. 4. application should guarantee that minimum and maximum du ty cycle fall between 20-85% to meet the specified range.
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 6 FAN5346 ? series boost led driver with pwm dimming interface typical characteristics v in = 3.6v, t a = 25 c, i led = 25ma, l = 10h, c out = 1.0f, and c in = 10.0f. 50% 60% 70% 80% 90% 5 10152025 efficiency led current (ma) v in=2.5v v in=2.7v v in=3.6v v in=4.2v vin=4.5v 50% 60% 70% 80% 90% 5 10152025 efficiency led current (ma) v in=2.5v v in=2.7v v in=3.6v v in=4.2v vin=4.5v figure 4. 3 leds: efficiency vs. led current vs. input voltage figure 5. 4 leds: efficiency vs. led current vs. input voltage 50% 60% 70% 80% 90% 5 10152025 efficiency led current (ma) v in=2.5v vin=2.7v v in=3.6v vin=4.2v v in=4.5v 50% 60% 70% 80% 90% 5 10152025 efficiency led current (ma) v in=2.5 v v in=2.7 v v in=3.6 v v in=4.2 v v in=4.5 v figure 6. 5 leds: efficiency vs. led current vs. input voltage figure 7. 6 leds: efficiency vs. led current vs. input voltage 50% 60% 70% 80% 90% 5 10152025 efficiency led current (ma) v in=2.5v v in=2.7v vin=3.6v v in=4.2v v in=4.5v 50% 60% 70% 80% 90% 5 10152025 efficiency led current (ma) vin=2.9v v in=3.6v vin=4.2v v in=4.5v figure 8. 7 leds: efficiency vs. led current vs. input voltage figure 9. 8 leds: efficiency vs. led current vs. input voltage
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 7 FAN5346 ? series boost led driver with pwm dimming interface typical characteristics v in = 3.6v, t a = 25 c, i led = 25ma, l = 10h, c out = 1.0f, and c in = 10.0f. 50% 60% 70% 80% 90% 2.5 3.0 3.5 4.0 4.5 efficiency input voltage (v) -40c +25c +85c 50% 60% 70% 80% 90% 2.5 3.0 3.5 4.0 4.5 efficiency input voltage (v) -40c +25c +85c figure 10. efficiency vs. input voltage vs. temperature for 5 leds in series figure 11. efficiency vs. input voltage vs. temperature for 7 leds in series -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 2.5 3.0 3.5 4.0 4.5 delta feedback (mv) input voltage (v) -40c +25c +85c 1000 1050 1100 1150 1200 1250 2.5 3.0 3.5 4.0 4.5 frequency (khz) input voltage (v) -40c +25c +85c figure 12. delta of v fb over input voltage and temperature for 7 leds with l=10h and c out =1.0f figure 13. frequency vs. input voltage vs. temperature 18.5 19.0 19.5 20.0 20.5 21.0 2.5 3.0 3.5 4.0 4.5 ovp (v) input voltage (v) 5 leds l = 10h c out = 1.0f i led = 25ma 29.0 29.5 30.0 30.5 31.0 31.5 2.5 3.0 3.5 4.0 4.5 ovp (v) input voltage (v) 7 leds l = 10h c out = 1.0f i led = 25ma figure 14. ovp vs. input voltage: FAN5346s20x figure 15. ovp vs. input voltage: FAN5346s30x
? 2011 fairchild semiconductor corp oration www.fairchildsemi.com FAN5346 ? rev. 1.0.1 8 FAN5346 ? series boost led driver with pwm dimming interface typical characteristics v in = 3.6v, t a = 25 c, i led = 25ma, l = 10h, c out = 1.0f, and c in = 10.0f. figure 16. shutdown current vs. input voltage figure 17. quiescent current vs. input voltage figure 18. led current vs. duty cycle, f pwm = 20khz figure 19. line t ransient response for 5 leds figure 20. line transient response for 6 leds figure 21. line transient response for 7 leds 0.00 0.20 0.40 0.60 0.80 2.50 3.00 3.50 4.00 4.50 shutdown current (a) v in (v) 225 230 235 240 245 250 255 260 265 2.50 3.00 3.50 4.00 4.50 quiescent current (a) v in (v) 0 5 10 15 20 25 0 20406080100 led current (ma) duty cycle (%)
? 2011 fairchild semiconductor corp oration www.fairchildsemi.com FAN5346 ? rev. 1.0.1 9 FAN5346 ? series boost led driver with pwm dimming interface typical characteristics v in = 3.6v, t a = 25 c, i led = 25ma, l = 10h, c out = 1.0f, and c in = 10.0f. figure 22. startup waveform for switch voltage, inductor current, v fb , and en for 5 leds figure 23. steady-state waveform for v out , switch voltage, and i nductor current for 5 leds figure 24. startup waveform for switch voltage, inductor current, v fb , and en for 6 leds figure 25. steady-state waveform for v out , switch voltage, and i nductor current for 6 leds figure 26. startup waveform for switch voltage, inductor current, v fb , and en for 7 leds figure 27. steady-state waveform for v out , switch voltage, and i nductor current for 7 leds
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 10 FAN5346 ? series boost led driver with pwm dimming interface circuit description overview the FAN5346 is an inductive current-mode boost serial led driver that achieves led current regulation by maintaining 0.250v across the r set resistor. the current through the led string (i led ) is given by: set led r i 250 . 0 = (1) the voltage v out is determined by the sum of the forward voltages across each led, plus the voltage across r set , which is always 250mv. driving eight leds in series FAN5346s30x can drive 8 leds in series, but the minimum input voltage (v in ) must be greater than or equal to 2.9v, while the forward voltage of the white led should be less than or equal to 3.2v, and the maximum led current cannot exceed 20ma to maintain stable operation. uvlo and soft-start if en has been low for more than 1ms, the ic may initiate a ?cold start? soft-start cycle when en rises, provided v in is above the uvlo threshold. pwm dimming the FAN5346 uses a pwm signal to directly modulate output current in the led string to vary the perceived led brightness. when the en pin is held high, the fb voltage is 250mv. this voltage is reduced when a pwm signal is applied to the en pin, thereby enabling the leds to be dimmed. the fb voltage is given by the equation: mv dutycycle v fb 250 = (2) where dutycycle = the duty cycle of the pwm signal and 250mv is the internal reference voltage. figure 28 illustrates how the FAN5346 divides the internal 250mv reference voltage at the duty cycle of the pwm signal. a low-pass filter filters the pwm signal, which then is input into the error amplifier as the reference voltage for the fb pin. figure 28. block diagram of fb and en circuit for pwm dimming over-current and short-circuit detection the boost regulator employs a cycle-by-cycle peak inductor current limit of 300ma (typical) and 750ma (typical) for FAN5346s20x and FAN5346s30x, respectively. over-voltage / open-circuit protection if the led string is an open circuit, fb remains at 0v and the output voltage continues to incr ease in the absence of an over- voltage protection (ovp) circuit. the FAN5346s20x ovp circuit disables the boost regulator when v out exceeds 20v and continues to keep the regulator off until v out drops below 19v. for FAN5346s30x, the ovp is 30v and it turns back on when v out is below 29v thermal shutdown when the die temperature exceeds 150c, a reset occurs and remains in effect until the die cools to 115c; at which time, the circuit is allowed to begin the soft-start sequence.
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 11 FAN5346 ? series boost led driver with pwm dimming interface application information the reference schematic diagram is shown in figure 29. FAN5346 is able to drive up to eight leds with input voltage equal to or greater than 2.9v (v in 2.9v). however, the number of leds that can be used FAN5346 depends on forward voltage. it is recommended that the forward voltage (v f ) of the white led be no gr eater than 3.2v and the maximum led current be 20ma. fan5345 can be also used as a boost convertor by connect the v out point to the load directly. the return trace of the load should also return to gnd through a sense resistor (r1). figure 29. reference application schematic diagram component placement and pcb recommendations FAN5346 switches at 1.2mhz to boost the output voltage. component placement and pcb layout need to be carefully taken into consideration to ensure stable output and to prevent generation of noise. fi gure 30 is a portion of the evaluation board layout. the critic al layout elements are: the l1, c in , c in return trace, c out , and the c out return trace. figure 30. reference pcb layout input capacitor and return trace the input capacitor is the first priority in a switching buck or boost regulator pcb layout. a stable input source (v in ) enables a switching regulator to deliver its best performance. during the regulator?s operation, it is switching at a high frequency, which makes the load of c in change dynamically since it is trying to make the input source vary at the same switching frequency as the regu lator. to ensure a stable input source, c in needs to hold enough energy to minimize the variation at the input pin of the regulator. for c in to have a fast response of charge / discharge, the trace from c in to the input pin of the regulator and the return trace from gnd of the regulator to c in should be as short and wide as possible to minimize trace resistance, inductance, and capacitance. during operation, the current flow from c in through the regulator to the load and back to c in contains high-frequency variation due to switching. trace resistance reduces the overall efficiency due to i 2 r loss. even a small trace inductance could effectiv ely yield ground variation to add noise on vout. the input c apacitor should be placed close to the vin and gnd pins of the regulator and traces should be as short as possible. avoid routing the return trace through different layers because vias have strong inductance effect at high frequencies. if routing to other pcb layers is unavoidable, place vias next to the vin and gnd pins of the regulator to minimize the trace distance. output capacitor and return trace the output capacitor serves t he same purpose as the input capacitor, but also maintains a stable output voltage. as explained above, the current travels to the load and back to the c out gnd terminal. c out should be placed close to the vout pin. the traces of c out to l1, vout, and the return
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 12 FAN5346 ? series boost led driver with pwm dimming interface trace from load to c out should be as short and wide as possible to minimize trace resistance and inductance. to minimize noise coupling to load, a small-value capacitor can be placed between vout and c out to route high-frequency noise back to gnd before it gets to the load. inductor inductor (l1) should be placed as close to the regulator as possible to minimize trace resistance and inductance for the reasons explained above. sense resistor the sense resistor provides a feedback signal for the regulator to control output voltage. a long trace from the sense resistor to the fb pin couples noise into the fb pin. if noise is coupled into the fb pi n, it causes unstable operation of the switching regulator, which affects application performance. the return trace from the sense resistor to the fb pin should be short and away from any fast-switching signal traces. the ground plane under the return trace is not necessary. if the ground plane under the return trace is noisy; but not the same ground plane as the regulator; the noise could be coupled into the fb pin through pcb parasitic capacitance, yielding noisy output. as shown in figure 30; c in , c out , and l1 are all placed next to the regulator. all traces are on the same layer to minimize trace resistance and inductance. total pcb area, not including the sense resistor, is 67.2mm 2 (7.47mm x 8.99mm) . table 1. recommended external components inductor (l) part number manufacturer 10.0h lqh43mn100k03 murata nlcv32t-100k-pfr tdk vlf3010at-100mr49-1 tdk dem2810c 1224-as-h-100m toko minimum c out 1.0f cv105x5r105k25at avx / kyocera minimum c in 10.0f grm21br71a106ke51l murata schottky diode n/a rbs520s30 fairchild semiconductor n/a rb520s-30 rohm
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 13 FAN5346 ? series boost led driver with pwm dimming interface physical dimensions figure 31. 6-lead, supersot?-6, jedec mo-193, 1.6mm wide package drawings are provided as a service to customers considering fairchild component s. drawings may change in any manner wit hout notice. please note the revision and/or date on the drawing and contact a fairchild semi conductor representative to verify or o btain the most recent revision. package specific ations do not expand the terms of fairchild?s worldwide terms and conditi ons, specifically the warranty therein, which covers fairchild products. always visit fairchild semiconductor?s online packa ging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/ .
? 2011 fairchild semiconductor corporation www.fairchildsemi.com FAN5346 ? rev. 1.0.1 14 FAN5346 ? series boost led driver with pwm dimming interface

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