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aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 1 switchreg ? typical application general description the aat1270 is a high-efficiency, high-current boost converter capable of 1a maximum output current. it is an ideal power solution for led photo flash appli- cations in all single-cell lithium-ion / polymer battery operated products. the aat1270 maintains output current regulation by switching the internal high-side and low-side switch transistors. the transistor switches are pulse-width modulated at a fixed frequency of 2mhz. the high switching frequency allows the use of a small induc- tor and output capacitor, making the aat1270 ideal- ly suited for small battery-powered applications. analogictechs proprietary s 2 cwire ? (simple serial control ? ) serial digital interface is used to enable, disable and set the movie mode current level for the flash leds to one of 16 levels. the aat1270 also includes a separate flash enable input to initiate both flash/strobe operation and the default timer, which can be used to terminate a flash event after a user- programmed delay or as a safety feature. a flash inhibit pin is also included which reduces flash cur- rent to movie mode level during high battery demand. the maximum flash and movie mode current is set by one external resistor; the ratio between flash and movie mode current is set at approximately 7.3:1. one or two leds can be connected to the aat1270; when two leds are used, the output current is matched between each diode. the aat1270 contains over-voltage protection and a thermal management system to protect the device in the event of an output open-circuit and short-circuit condition respectively. built-in circuitry prevents exces- sive inrush current during start-up. the shutdown fea- ture reduces quiescent current to less than 1.0a. the aat1270 is available in a pb-free, thermally- enhanced 14-pin 3x3mm stdfn package. features ? input voltage range: 2.7v to 5.5v ? dual channel output up to 1a regulated output current (0.5a per channel) ? up to 85% efficiency with small magnetics ? 2 mhz switching frequency ? separate flash enable input ? separate flash inhibit input ? single resistor sets flash and movie mode current fixed flash-to-movie mode current ratio ? 16-level movie mode current via s 2 cwire? ? user-programmable safety timer ? true load disconnect ? input current limit ? over-voltage (open led, open circuit), short- circuit, and over-temperature protection ? shutdown current: < 1.0a ? small inductor solution: 1h (0.9mm in height) ? 14-pin stdfn 3x3 package ? -40 to +85c temperature range applications ? camcorder video light (torch light) ? cellphones / smartphones ? digital still cameras (dsc) ? led photo flash light (strobe light) ? mobile handsets ? mp3 players ? pdas and notebook pcs aat1270 r set 162k v battery c in 2.2f c t 47nf l1 1h in sw out flouta ct en/set flinh rset agnd pgnd flen movie mode enable and set flash enable flash inhibit floutb flgnd c out 2.2f gnd flash leds lumiled lxcl-pwf1 or equivalent
pin descriptions pin # symbol function 1 ct flash timer control input. connect a capacitor between ct and agnd to set maximum dura- tion for the flash pulse. a 47nf ceramic capacitor sets the flash timer to 1s. to disable the flash timer, connect ct to agnd. 2 en/set enable and movie mode serial control input. en/set is the s 2 cwire programming input to adjust the movie mode current level to one of 16 different levels based on the maximum cur- rent/7.3 set via the rset pin. 3 flen flash enable pin. a low-to-high transition on the flen pin initiates a flash pulse and starts the flash timer. 4 agnd analog ground pin. connect agnd to pgnd, gnd, and flgnd at a single point as close to the aat1270 as possible. 5 in power input. connect in to the input power supply voltage. connect a 2.2f or larger ceram- ic capacitor from in to pgnd as close as possible to the aat1270 6 sw boost converter switching node. connect a 1h inductor between sw and in. 7 pgnd power ground pin. connect pgnd to agnd, gnd, and flgnd at a single point as close to the aat1270 as possible. 8 out power output of the boost converter. connect a 2.2uf or larger ceramic capacitor from out to pgnd as close as possible to the aat1270. connect out to the anode(s) of the flash led(s). 9 gnd ground pin. connect gnd to pgnd, agnd, and flgnd at a single point as close to the aat1270 as possible. 10 flinh flash inhibit pin. flinh is an active high control input with an internal 200k resistor to agnd. a low-to-high transition on the flinh pin reduces flouta and floutb output cur- rents to the maximum (default) movie-mode current level for the duration of flinh. strobing the flinh pin low to high does not reset the flash timer. 11 floutb flash output b. connect cathode of flash ledb to flout b. for a single flash led, connect floutb and flouta together. for two flash leds, each output will conduct 50% of the total flash output current. 12 flgnd flash ground pin. connect flgnd to pgnd, gnd, and agnd at a single point as close to the aat1270 as possible 13 flouta flash output a. connect cathode of flash led a to flouta. for a single flash led, connect flouta and floutb together. for two flash leds, each output will conduct 50% of the total flash output current. 14 rset flash current setting input. a 162k resistor from rset to agnd sets the maximum flash cur- rent available at flouta or floutb to 500ma. each flouta and floutb channel will con- duct 50% of the maximum programmed current. the aat1270s flash-to-movie-mode ratio is fixed at 7.3. ep exposed paddle (bottom); connect ep to pgnd as close as possible to the aat1270. aat1270 1a step-up current regulator for flash leds 2 1270.2007.07.1.0
aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 3 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at c ondi- tions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. pin configuration stdfn33-14 (top view) absolute maximum ratings 1 t a = 25c unless otherwise noted. recommended operating conditions symbol description value units ja thermal resistance 50 c/w p d maximum power dissipation 2 w symbol description value units in, sw, out maximum rating -0.3 to 6.0 v rset, en/set, flen, flinh, ct, maximum rating v in + 0.3 v flouta, floutb t j operating temperature range -40 to 150 c t s storage temperature range -65 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c ct flen agnd 1 in sw pgnd rset flgnd floutb flinh gnd out en/set 2 3 4 5 6 7 12 flout a 12 11 11 10 9 8
aat1270 1a step-up current regulator for flash leds 4 1270.2007.07.1.0 1. the aat1270 is guaranteed to meet performance specification from 0?c to +70?c. specification over the C40?c to +85c operati ng temperature range is assured by design, characterization and correlation with statistical process controls. electrical characteristics 1 v in = 3.6v; c in = 2.2f; c out = 2.2f; r set = 162k; t a = 0c to 70c, unless otherwise noted. typical val- ues are t a = 25c. symbol description conditions min typ max units power supply v in input voltage range 2.7 5.5 v v out(max) maximum output voltage 5.5 v flen = in, set fl load = 1a 0.57 1 i in(q) v in supply current en/set = in, set fl load = 0a, 0.23 ma r set = 162k i shdn(max) v in shutdown current en/set = flen = flinh = gnd 1 a i fl(total) total output current, flash mode r set = 162k ; flouta + floutb 800 1000 1200 ma i fl(match) flouta and floutb current 10 % matching i mm(total) total output current, movie mode r set = 162k ; movie mode current 137 ma set = 100%;flouta + floutb f osc switching frequency t a = 25?c 1.5 2.0 2.5 mhz t default default on time c t = 47nf 1 s t sd thermal shutdown threshold 140 c t sd(hys) thermal shutdown hysteresis 15 c en/set/ flen/ flinh logic control v en/set(l) , en/set, flen input low 0.4 v v flen(l) threshold v en/set(h) , ) en/set, flen input high 1.4 v v flen(h threshold i en/set en/set input leakage current v en/set = v in = 5v -1 1 a i flen flen input leakage current v flen = v in = 5v -1 1 a v t(flinh) flinh input threshold voltage ? v in v r in(flinh) flinh input resistance to agnd 200 k t en/set(low) en/set serial interface low time 0.3 75 s t en/set(hi _ min) minimum en/set high time 50 ns t en/set(hi _ max) maximum en/set high time 75 s t en/set(off) en/set off timeout 500 s t en/set(lat) en/set latch timeout 500 s t flen _ on flen on delay time en/set = gnd 100 s t flen _ off flen off delay time en/set = gnd 20 s t flinh _ on flinh on delay time 100 s t flinh _ off flinh off delay time 5 s
typical characteristics aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 5 flash mode current matching vs. temperature (500ma/ch) temperature (c) led current (ma) 485 490 495 500 505 510 515 -40 -15 10 35 60 85 flouta floutb movie mode current matching vs. temperature (68.5ma/ch) temperature (c) led current (ma) 65.5 66.0 66.5 67.0 67.5 68.0 68.5 69.0 69.5 70.0 70.5 -40 -15 10 35 60 85 flouta floutb movie mode led current accuracy vs. input voltage (68.5ma/ch) input voltage (v) led current accuracy (%) -10 -5 0 5 10 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 floutb flouta switching frequency vs. input voltage (en/set = flen = 0v) input voltage (v) switching frequency (mhz) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c shutdown current vs. input voltage (en/set = flen = 0v) input voltage (v) shutdown current (a) 0 0.02 0.04 0.06 0.08 0.1 0.12 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 efficiency vs. input voltage (movie and flash mode) input voltage (v) efficiency (%) 40 45 50 55 60 65 70 75 80 85 90 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 68.5ma (movie) 34.25ma (movie) 13.7ma (movie) 500ma (flash)
typical characteristics aat1270 1a step-up current regulator for flash leds 6 1270.2007.07.1.0 en/set off timeout vs. input voltage input voltage (v) t en/set(off) (s) 200 250 300 350 400 450 500 550 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c en/set latch timeout vs. input voltage input voltage (v) t en/set(lat) (s) 200 250 300 350 400 450 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5. 5 85c -40c 25c en/set, flen input low threshold vs. input voltage input voltage (v) v en/set(l) (v) 0.2 0.4 0.6 0.8 1.0 1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25c 85c -40c en/set, flen input high threshold vs. input voltage input voltage (v) v en/set(h) (v) 0.2 0.4 0.6 0.8 1.0 1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25c 85c -40c movie mode output ripple (68.5ma/ch) time (125ns/div) output voltage (top) (v) switching voltage (middle) (v) inductor current (bottom) (a) 3.16 3.18 3.20 0.0 0.2 0.4 0v 3.2v flash mode output ripple (500ma/ch) time (250ns/div) output voltage (top) (v) switching voltage (middle) (v) inductor current (bottom) (a) 3.0 3.2 3.4 1.5 2.0 2.5 0v 4v
typical characteristics aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 7 movie mode turn on (68.5ma/ch) time (100s/div) v out (2v/div) v sink (2v/div) en/set (2v/div) i led (100ma/div) 0a 0v 0v 0v movie mode turn on (13.7ma/ch) time (200s/div) v out (2v/div) v sink (2v/div) en/set (2v/div) i led (100ma/div) 0a 0v 0v 0v flash inhibit on delay time (en/set = 0v; flen = 3.3v; 500ma/ch) time (100s/div) voltage (v) v sink (2v/div) v out (2v/div) flinh (2v/div) i led (500ma/div) 0 2 4 1a 0v flen on delay time vs. input voltage input voltage (v) t flen_on (s) 0 20 40 60 80 100 120 140 160 180 200 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25c -40c 85c movie mode to flash mode turn on (68.5ma/ch to 500ma/ch) time (100s/div) voltage (v) v out (2v/div) v sink (2v/div) flen (2v/div) i led (1a/div) 0 2 4 1 a 0v flash mode turn on (500ma/ch) time (100s/div) v out (2v/div) v sink (2v/div) flen (2v/div) i in (1a/div) 0a 0v 0v 0v
typical characteristics aat1270 1a step-up current regulator for flash leds 8 1270.2007.07.1.0 movie mode line transient (68.5ma/ch; v in = 4.2v to 3.6v) time (50s/div) i led (ac coupled) (50ma/div) v in (500mv/div) 4.2v 3.6v movie mode current transition (68.5ma/ch to 13.7ma/ch) time (200s/div) v out (ac coupled) (100mv/div) v sink (ac coupled) (200mv/div) en/set (2v/div) i led (100ma/div) 0a 3.3v
aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 9 functional block diagram functional description the aat1270 is a boost converter with a current regulated output designed to drive high current white leds used in flash/movie light applications. the maximum flash current is set by an external resistor, r set , which not only sets the flash current but also sets the maximum movie mode current reduced by a factor of 7.3. a flash pulse is initiated by switching the flen (flash enable) pin from low to high, which initiates the flash pulse and also starts the internal timer. the maximum flash time is deter- mined by an external timing capacitor connected to the ct pin. the flash duration can be set from 50ms to a maximum of 1s. the flash timer will terminate the flash current regardless of the status of the flen pin. this can be either used as a simple flash timing pulse or as a safety timer in the event of a control logic malfunction to prevent the led from over-heating. if the safety timer is not needed in the application, it can be disabled by connecting the ct pin directly to agnd. for applications using two flash leds, each diode can be connected to its corresponding current sink (flouta or floutb) and the output current will be equally shared. in single flash led applications, the two current sinks can be connected together to apply the full output current into the led. sw pgnd flout a agnd control rset in ct floutb flgnd out en/set flen flinh gnd 200k
aat1270 1a step-up current regulator for flash leds 10 1270.2007.07.1.0 if one sink pin (flouta or floutb) is not used, the unused current sink must be directly connected to out, which disables that channel. the movie-mode output current is controlled by the en/set pin, which uses a single-wire s 2 cwire interface to adjust the output current to one of 16 different levels. as shown in table 1, the current settings are in logarithmic scale where each code is 1db below the previous code. the flen signal takes priority over movie-mode operation. in mobile gsm systems where the phone remains in constant contact with the base station by regular communication, a flinh pin is provided to prevent the camera flash and pa transmission pulses from occurring simultaneously, potentially causing the bat- tery voltage to drop below the systems undervoltage lockout threshold (uvlo) or creating unwanted emi. during a flash event, strobing the flinh pin low-to- high will reduce the led current to the maximum movie mode current level for the duration of flinh. strobing flinh high-to-low will instruct the aat1270 to revert the flash led current to its default (maxi- mum) level assuming that the flen pin is still active (high) and that the flash timer has not expired. over-temperature protection thermal protection disables the aat1270 when internal power dissipation becomes excessive, as it disables both mosfets. the junction over-tem- perature threshold is 140c with 15c of tempera- ture hysteresis. the output voltage automatically recovers when the over-temperature fault condition is removed. over-voltage protection (open led, open circuit) the aat1270s output voltage is limited by internal over-voltage protection circuitry, which prevents damage to the aat1270 from open led or open circuit conditions. during an open circuit, the output voltage rises and reaches 5.5v (typical), and the ovp circuit dis- ables the switching, preventing the output voltage from rising higher. once the open circuit condition is removed, switching will resume. the controller will return to normal operation and maintain an average output voltage. applications information led selection the aat1270 is specifically designed to drive white flash leds (typical forward voltage of 2.5v to 4.5v). since the flouta and floutb input cur- rent sinks are matched with low voltage depend- ence; the led-to-led brightness will be matched regardless of the individual led forward voltage (v f ) levels. flash mode led current the led current is controlled by the r set resistor. for maximum accuracy, a 1% tolerance resistor is recommended. flouta and floutb can be pro- grammed up to a maximum total flash current of 1a, or up to 500ma per channel. flouta and floutb output current is matched across the pro- gramming range. the maximum flash current in each flouta and floutb is set by the r set resistor and can be cal- culated using the following equation: movie mode led current in the default movie mode, the corresponding flouta/floutb movie mode current can be cal- culated: for example, if an r set value of 162k is chosen, then the flouta/floutb flash current is set to 500ma. for movie mode operation, the maximum current available at either flouta or floutb is then: alternatively, the aat1270 s 2 cwire interface pro- grams the movie mode current at a reduced level. the flouta/floutb movie-mode current can be adjusted in logarithmic fashion to one of 16 steps. table 1 illustrates approximate movie mode levels i flout[a/b]max 7.3 500ma 7.3 i movie mode[a/b] = = = 68.5m a 81k ? a r set 81k ? a 162k i flouta = i floutb = = = 500ma per channel i flout[a/b]max 7.3 i movie mode[a/b] =
aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 11 to which the aat1270 movie mode operation can be programmed. table 1: programming movie mode current via s 2 cwire (%). s 2 cwire serial interface the simple serial control (s 2 cwire) serial interface records rising edges at the en/set pin and decodes them into 16 different states. the s 2 cwire serial interface has flexible timing. data can be applied at speeds faster than 1mhz, or at much slower speeds, such as 15khz. after data is applied, en/set is strobed high and held high to latch the data. once the signal applied at the en/set pin has been held in the logic high state for time longer than t lat (500s), the programmed current becomes active and the internal data register is reset to zero. for subsequent current level pro- gramming, the number of rising edges correspon- ding to the desired code must be applied to the en/set pin. s 2 cwire percentage of maximum data movie mode current (%) 1 100 289 379 471 563 656 750 8 44.7 9 39.8 10 35.5 11 31.6 12 28.2 13 25.1 14 22.4 15 20 16 0 figure 1: s 2 cwire serial interface timing 1 en/set 2 n-1 n 16 data reg 0n-1 0 t hi t lo t lat t off
aat1270 1a step-up current regulator for flash leds 12 1270.2007.07.1.0 flash timer the aat1270a includes a timer circuit that enables the flash current sinks for a programmed period of time. this feature eliminates the need for an exter- nal, housekeeping baseband controller to contain a safety delay routine. it also serves as a protection feature to minimize thermal issues with the flash leds in the event an external controllers flash soft- ware routine experiences hang-up or freeze. the flash timeout t can be calculated by the fol- lowing equation: where t is in seconds and c t is the capacitance of the timer capacitor in f. for example, using a 47nf capacitor for c t sets the flash timeout to: the relationship between capacitance of the timer capacitor and the flash timeout is illustrated in figure 2. figure 2: timer capacitor vs. flash timeout. timing diagram flash timeout (ms) capacitance (nf) 0 5 10 15 20 25 30 35 40 45 50 0 100 200 300 400 500 600 700 800 900 1000 flash timeout = 21.5s/f 0.047f = 1s t = 21.5s/f c t led current (0ma) movie mode flash flash flash times out set by ct flash times out flash lowered to movie-mode during flinh en/set flash enable flash inhibit t dly(ct ) flash lowered to movie-mode during flinh data to movie-mode level flash t dly(ct ) flash flash
aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 13 selecting the boost inductor the aat1270 controller utilizes pwm control and the switching frequency is fixed. to maintain 2mhz maximum switching frequency and stable opera- tion, an 1h output inductor is recommended. manufacturers specifications list both the inductor dc current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. measurements at full load and high ambient temperature should be performed to ensure that the inductor does not sat- urate or exhibit excessive temperature rise. the output inductor (l) is selected to avoid satura- tion at minimum input voltage and maximum output load conditions. worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. at high load the switching frequency is somewhat diminished, resulting in higher i peak . bench meas- urements are recommended to confirm actual i peak and to ensure that the inductor does not saturate at maximum led current and minimum input supply voltage. the rms current flowing through the boost induc- tor is equal to the dc plus ac ripple components. under worst-case rms conditions, the current waveform is critically continuous. the resulting rms calculation yields worst-case inductor loss. the rms current value should be compared against the inductor manufacturer's temperature rise, or thermal derating, guidelines: for a given inductor type, smaller inductor size leads to an increase in dcr winding resistance and, in most cases, increased thermal impedance. winding resistance degrades boost converter efficiency and increases the inductors operating temperature: selecting the boost capacitors in general, it is good design practice to place a decoupling capacitor (input capacitor) between the in and gnd pins. an input capacitor in the range of 2.2f to 10f is recommended. a larger input capacitor in this application may be required for sta- bility, transient response, and/or ripple performance. the high output ripple inherent in the boost con- verter necessitates the use of low impedance out- put filtering. multi-layer ceramic (mlc) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (esr) and equivalent series inductance (esl), and are well suited for use with the aat1270 boost regulator. mlc capacitors of type x7r or x5r are recom- mended to ensure good capacitance stability over the full operating temperature range. table 2: typical suggested surface mount inductors max inductance dc i sat dcr size (mm) manufacturer part number (h) current (a) (m?) (lxwxh) type murata lqm2hpn1r0mg0 1.0 1.6 55 2.5x2.0x0.9 multilayer murata lqh3npn1r0g0 1.0 1.58 110 3.0x3.0x1.0 wirewound coilcraft lps3010 1.0 1.6 85 3.0x3.0x1.0 wirewound cooper bussmann sd3110 1.0 1.47 68.3 3.1x3.1x1.0 wirewound cooper bussmann sd3812 1.0 3.89 30 4.0x4.0x1.2 wirewound sumida cdh38d11/s 1.0 2.8 39 4.0x4.0x1.2 wirewound p loss(inductor) = i rms 2 dcr i peak 3 rms i=
aat1270 1a step-up current regulator for flash leds 14 1270.2007.07.1.0 the output capacitor is selected to maintain the out- put load without significant voltage droop (v out ) during the power switch on interval. a ceramic out- put capacitor 2.2f is recommended (see table 3). typically, 6.3v or 10v rated capacitors are required for this flash led boost output. ceramic capacitors selected as small as 0603 are available which meet these requirements. mlc capacitors exhibit signifi- cant capacitance reduction with applied voltage. output ripple measurements should confirm that output voltage droop and operating stability are with- in acceptable limits. voltage derating can minimize this factor, but results may vary with package size and among specific manufacturers. to maintain stable operation at full load, the output capacitor should be selected to maintain v out between 100mv and 200mv. the boost converter input current flows during both on and off switch- ing intervals. the input ripple current is less than the output ripple and, as a result, less input capac- itance is required. table 3: typical suggested surface mount capacitors. figure 3: aat1270 evaluation board schematic. capacitance voltage manufacturer part number (f) rating (v) temp co. case size murata grm185r60j225ke26 2.2 6.3 x5r 0603 murata grm188r71a225ke15 2.2 10 x7r 0603 murata grm21br70j225ka01 2.2 6.3 x7r 0805 murata grm21br71a225ka01 2.2 10 x7r 0805 murata grm219r61a475ke19 4.7 10 x5r 0805 murata grm21br71a106ke51 10 10 x7r 0805 2.2 f c2 1h l1 2.2f c1 162k r1 d1 dc+ vout d2 0 jp1 vdd 1 gp5 2 gp4 3 gp3 4 gp2 5 gp1 6 gp0 7 vss 8 pic12f675 u2 1f c4 100k r3 100k (opt) r4 330 r6 1 2 3 4 5 0 flen sw2 led1 red 1 2 3 4 5 0 flinh sw 3 1 2 3 4 5 0 en/set sw1 10k r5 led2 grn 330 r7 dc- 0 jp7 0 jp2 47nf c3 100k r2 jp3 jp4 10k r8 l1 murata lqm2hpn1r0mg0 1h 1.6a 55m c1, c2 murata grm188r71a225ke15 2.2f 0603 x7r 10v c3 murata grm155r71a473ka01 47nh 0402 x7r 10v in 5 ct 1 sw 6 out 8 enset 2 flen 3 pgnd 7 agnd 4 gnd 9 flinh 10 flb 11 flgnd 12 fla 13 rset 14 aa t1270 stdfn33-14 u1 en/set jp5 mcu jp6
aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 15 figure 4: aat1270 evaluation board figure 5: aat1270 evaluation board top side layout. second layer. figure 6: aat1270 evaluation board figure 7: aat1270 evaluation board third layer. bottom side layout. pcb layout guidelines boost converter performance can be adversely affected by poor layout. possible impact includes high input and output voltage ripple, poor emi per- formance, and reduced operating efficiency. every attempt should be made to optimize the layout in order to minimize parasitic pcb effects (stray resist- ance, capacitance, and inductance) and emi cou- pling from the high frequency sw node. a suggest- ed pcb layout for the aat1270 1a step-up regula- tor is shown in figures 4 through 7. the following pcb layout guidelines should be considered: 1. minimize the distance from capacitor c in and c out s negative terminals to the pgnd pins. this is especially true with output capacitor c out , which conducts high ripple current from the output to the pgnd pins. 2. minimize the distance between l1 to in and switching pin sw; minimize the size of the pcb area connected to the sw pin. 3. maintain a ground plane and connect to the ic pgnd pin(s) as well as the pgnd connections of c in and c out . 4. consider additional pcb exposed area for the flash leds to maximize heatsinking capability. this may be necessary when using high current application and long flash duration application. 5. connect the exposed paddle (bottom of the die) to either pgnd or gnd. connect agnd, flgnd to gnd as close as possible to the package.
aat1270 1a step-up current regulator for flash leds 16 1270.2007.07.1.0 table 4: aat1270 evaluation board bill of materials. component part number description manufacturer u1 aat1270ifo 1a step-up current regulator for flash analogictech leds; stdfn33-14 package u2 pic12f675 8-bit cmos, flash-based c; 8-pin microchip pdip package sw1-sw3 pts645tl50 switch tact, spst, 5mm itt industries r1 chip resistor 162k?, 1%, 1/4w; 0402 vishay r2, r3, r4 chip resistor 100k?, 1%, 1/4w; 0603 vishay r5, r8 chip resistor 10k?, 5%, 1/4w; 0603 vishay r6, r7 chip resistor 330?, 5%, 1/4w; 0603 vishay jp1, jp2, jp7 chip resistor 0, 5% vishay c1, c2 grm188r71a225ke15 2.2f, 10v, x7r, 0603 murata c3 grm155r71a473ka01 47nf, 10v, x7r, 0402 murata c4 grm216r61a105ka01 1f, 10v, x5r, 0805 murata l1 lqm2hpn1r0mg0 multilayer, 1h, 1.6a, 55m? murata d1-d2 lxcl-pwf1 white flash led lumileds, philips led1 cmd15-21src/tr8 red led; 1206 chicago miniature lamp led2 cmd15-21vgc/tr8 green led; 1206 chicago miniature lamp jp3, jp4, jp5, jp6 prpn401paen conn. header, 2mm zip sullins electronics
aat1270 1a step-up current regulator for flash leds 1270.2007.07.1.0 17 ordering information package information 3 stdfn33-14 all dimensions in millimeters. package marking 1 part number (tape and reel) 2 stdfn33-14 xxxyy AAT1270IFO-T1 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . 3. the leadless package family, which includes qfn, tqfn, dfn, tdfn, and stdfn, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. a solder fillet at the exposed copper edge cannot be guaranteed and is not req uired to ensure a proper bottom solder connection. top view bottom view 3.000 all analogictech products are offered in pb-free packaging. the term pb-free means semiconductor products that are in compliance with current rohs standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. for more information, please visit our website at http://www.analogictech.com/pbfree.
aat1270 1a step-up current regulator for flash leds 18 1270.2007.07.1.0 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737- 4600 fax (408) 737- 4611 ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifications or to discontinue any product or service with- out notice. except as provided in analogictechs terms and conditions of sale, analogictech assumes no liability whatsoever, an d analogictech disclaims any express or implied war- ranty relating to the sale and/or use of analogictech products including liability or warranties relating to fitness for a part icular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. in order to minimize risks associated with the customers applications, adequa te design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. testing and other quality control techniques are utilized to the extent an alogictech deems necessary to support this warranty. specific testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trad emarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holder s.

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