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1 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 general description the aat1401 is a step-up single channel led driver with an input voltage range of 2.7v to 5.5v. the wide input voltage range, small solution size, advanced dimming features and high efficiency is suitable for led backlight solutions for single cell li-ion based equipment. a preci - sion, high voltage current sink maintains the maximum led current set by an external resistor from 10 to 31ma. the high switching frequency supports ultra small, low cost filtering components. two dimming controls are available; 32 dimming steps using the s 2 cwire? interface, and filtered pwm control. the frequency range of the pwm dimming extends up to 100 khz eliminating audible noise and suitable for cabc (content adaptive brightness control) applications. the device includes over-temperature protection and programmable over-voltage protection and recovers automatically when the faults are removed. the aat1401 is available in a 10-pin wafer-level chip scale package (wlcsp) and is rated over the -40c to +85c tempera - ture range. features? input voltage range: 2.7 to 5.5v ? drives up to 28v with 6 series leds at 31ma ? 1mhz switching frequency allows small external components ? up to 85% efficiency ? dimming control options: ? 32 steps - s 2 cwire single wire interface ? filtered pwm ? low operating current at 2.3ma ? shutdown current < 1a ? over-voltage protection for open-led faults ? over temperature protection ? ultra small, low profile 10-pin 1.55 x 1.15mm wlcsp package applications? digital still cameras (dsc) ? mobile handsets ? netbooks and notebooks ? portable media players ? white led drivers typical application lx ovp d1 v in : 2.7vC5.5v aat1401 cs l1 10h v out : up to 28vat 31ma c out 0.1f50v c in 4.7f in gnd en/set s 2 c r1 r2 r set 10k pgnd rset c comp 56nf comp pwm up to 6 wleds pwm downloaded from: http:///
2 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 pin descriptions pin # symbol function a1 lx switching node of boost converter. connect an inductor between lx and input supply (vin); schottky rectiier anode is connected between lx pin while cathode is connected to output capacitor. a2 in supply input for the ic. connect a 4.7f 6.3v/10v ceramic capacitor from this pin to gnd. a3 en/set enable on/off control and s 2 cwire interface input. b1 pgnd power ground pin. b3 pwm input pwm pin. pull high to disable the pwm dimming feature. c1 gnd ground pin. c3 comp compensation pin. connect a capacitor from this pin to gnd. compensation components are mainly related to the output capacitor valued. see the capacitor selection section in the application infor- mation section of this datasheet. d1 cs connect to the cathode of the last diode of the led string. d2 rset connect a resistor to gnd to set maximum led current up to 31ma. d3 ovp feedback pin for over-voltage protection. pin configuration wlcsp10 1.1 x1.5 (top view) a1 a2 a3 b1 c1 d1 d2 b3 c3 d3 downloaded from: http:///
3 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at conditions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. 2. mounted on an fr4 board. 3. check electrical characteristics. absolute maximum ratings 1 symbol description value units v in in to gnd, pgnd -0.3 to 6.0 v v lx lx to gnd, pgnd -0.3 to 34 v v cs sink to gnd, pgnd -0.3 to 28 v v en/set ,v pwm , v rset , v comp, v ovp en/set, pwm, rset, comp, ovp to gnd/pgnd -0.3 to in +0.3 v thermal information 2 symbol description value units ja thermal resistance 122 o c/w p d maximum power dissipation 820 mw t j maximum junction operating temperature -40 to +155 o c t lead maximum soldering temperature (at leads, 10 sec.) 300 recommended operating conditions symbol description min typ max units v in input supply voltage 2.7 5.5 v v out boosted output voltage v in + 3v v out 3 v l1 inductor value 4.7 10 22 h f pwm-f input filtered pwm frequency 100 100,000 hz t a ambient temperature range - 40 85 c downloaded from: http:///
4 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 1. the aat1401 is guaranteed to meet performance specification over the C40c to +85c operating temperature range, and is assured by design, characterization and correla - tion with statistical process controls. electrical characteristics 1 v in = 3.6v, c in = 4.7f, c out = 0.1f, l = 10h, r set = 10k?, t a = -40c to 85c unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units v in input voltage range 2.7 5.5 v v out maximum output voltage 28 v i q quiescent supply current v enset = v in 430 700 a i shdn input shutdown current v enset = 0v 1 a i qsw input switching current v enset = v in 2.3 ma r ds(on)n nmos on-resistance t a = 25c 650 m? maximum eficiency i out = 31ma 85 % f osc switching frequency t a = 25c 1.0 mhz t ss soft-start time v enset = v in to 95% of output regulation, c comp = 56nf 4 ms d max maximum duty cycle 94.0 % v ovp-t out over-voltage protection threshold v ovp rising 1.1 1.2 1.3 v v ovph over-voltage protection hysteresis 75 mv t sd over-temperature shutdown threshold 155 c t hys over-temperature shutdown hysteresis 15 c v cs current sink voltage i out = 31ma 500 mv i cs(acc) current sink accuracy r set = 10k 27.9 31.0 34.1 ma v rset rset voltage r set = 10k 1.206 v en/set v en/set (l) en/set v in = 2.7v to 5.5v 0.4 v v en/set (h) en/set v in = 2.7v to 5.5v 1.4 v t en/set(low) en/set input low time 0.3 75 s t en/set(hi_min) en/set minimum high time 100 ns t en/set(himax) en/set maximum high time 75 s t en/set(off) en/set input off timeout 500 s t en/set(lat) en/set latch timeout 500 s i en/set (lk) en input leakage v enset = 5v, v in = 5v -1 1 a pwm v pwm(l) logic threshold low 0.4 v v pwm(h) logic threshold high 1.4 v i pwm(lk) pwm input leakage v pwm = 5v, v in = 5v -1 1 a downloaded from: http:///
5 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 typical characteristics quiescent current vs. input voltage input voltage (v) quiescent current (a) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 380 400 420 440 460 480 500 85c25c -40c shutdown current vs. input voltage input voltage (v) shutdown current (a) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 0.00 0.02 0.04 0.06 0.08 0.10 85c25c -40c efficiency vs. output current (r set = 10k?, l = 10h, 6 les output current ( efficiency ( 08 16 24 32 41 22 02 8 61 42 23 0 21 01 82 6 30 35 40 45 50 55 60 65 70 75 80 85 90 v in = 2.7v v in = 3.0v v in = 3.6v v in = 4.2v v in = 5.0v v in = 5.5v led current accuracy vs. s 2 c (v in = 3.6v, l = 10h) s 2 c data current (ma) 19 17 25 33 51 32 12 9 0 4 8 12 16 20 24 28 32 r set = 10k r set = 15k r set = 20k r set = 25k r set = 30k sink current accuracy vs. temperature (v in = 3.6v, r set = 1k? temperature (c current (ma -4 0- 15 10 35 60 85 18.0 18.8 19.6 20.4 21.2 22.0 sink current accuracy vs. temperature (v in = 3.6v, r set = 1k? temperature (c current (ma -4 0- 15 10 35 60 85 30.0 30.4 30.8 31.2 31.6 32.0 downloaded from: http:///
6 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 typical characteristics led current accuracy vs. input voltage (v in = 3.6v, r se = ? input voltage (v current (a 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 18.8 19.2 19.6 20.0 20.4 20.8 21.2 startup time vs. c comp (6 wleds) c comp (nf) t su (ms) 10 20 30 40 50 60 70 80 90 100 0 3 6 9 12 15 en input high threshold voltage vs. input voltage input voltage (v) v en(h) (v) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 0.5 0.6 0.7 0.8 0.9 1.0 1.1 85c25c -40c en input low threshold voltage vs. input voltage input voltage (v) v en(l) (v) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 0.4 0.5 0.6 0.7 0.8 0.9 1.0 85c25c -40c nmos r ds(on)n vs. input voltage input voltage (v) r ds(on) (m) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 400 500 600 700 800 900 1000 85c25c -40c downloaded from: http:///
7 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 typical characteristics pwm input high threshold voltage vs. input voltage input voltage (v) v pwm(h) (v) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 0.5 0.6 0.7 0.8 0.9 1.0 1.1 85c25c -40c pwm input low threshold voltage vs. input voltage input voltage (v) v pwm(l) (v) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 0.4 0.5 0.6 0.7 0.8 0.9 1.0 85c25c -40c ovp high threshold voltage vs. input voltage input voltage (v) v ovp(h) (v) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 1.15 1.17 1.19 1.21 1.23 1.25 85c25c -40c ovp low threshold voltage vs. input voltage input voltage (v) v ovp(l) (v) 2. 73 .1 3. 53 .9 4. 34 .7 5. 15 .5 1.00 1.04 1.08 1.12 1.16 1.20 85c25c -40c startup waveform (v in = 3.6v; c in = 4.7f, c out = .f, c co = 6f, st = ?, 6 tme (mv n (vv v out (vv i in (mv i (mv 0 00 0 turn off (v in = 3.6v; c in = 4.7f, c out = 0.1f, c comp = 56nf, r set = 10?, 6 e t (100 en (5v v out (0v i in (00 i e (0 0 0 0 0 downloaded from: http:///
8 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 typical characteristics operation waveform (v in = 3.6v; c in = 4.7f, c out = .f, c co = 6nf, t = ?, 6 w time (iv v (viv v out (c (mviv i inucto (miv i (miv 0 0 0 0 operation waveform (v in = 3.6v; c in = 4.7f, c out = .f,c co = 6nf, t = ?, w = , t ce, 6 w time (iv v (viv v out (c (mviv i inucto (miv i (miv 0 00 0 led current transient (v in = 3.6v; c in = 4.7f, c out = 0.f, c co = 6nf, et = 0?, = 0, dut ce = 00 t 0, 3 t tie (si (vi v out (0vi i in (00i i led (0i 0 0 0 0 led current transition (v in = 3.6v; c in = 4.7f, c out = .f, c co = 6nf, et = ?, = , dut ce = to , 3 to tie (si (vi v out (vi i in (i i led (i 0 0 0 0 led current transient by s 2 cwire (v in = 3.6v; c in = 4.7 c t = . c c = 6n set = ? s 2 cwire data t 6 tie (si enset(vi v t (2vi i in (2i i led (2i 0 0 0 0 led current transient by s 2 cwire (v in = 3.6v; c in = 4.7 c t = . c c = 6n set = ? s 2 cwire data 6 t tie (si enset(vi v t (2vi i in (2i i led (2i 0 0 0 0 downloaded from: http:///
9 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 functional description the aat1401 is a small size, high efficiency, current mode controlled step-up converter led driver for up to 6 white leds. it is available with up to 28v output voltage to allow up to 6 series connected leds to be driven with currents up to 31ma. the device uses a single current sink to regulate the led current by controlling the output volt - age. the maximum led current is programmed by an external resistor with range from 10ma to 31ma. the led current dimming is controlled via one of two options, using either the s 2 cwire 32-step single-wire interface or pwm control. the over-voltage protection function is designed to pro - tect the boost converter during the fault of the open circuit of the led string. the over-temperature function is targeted to protect the converter if an over-tempera - ture fault occurs. the aat1401 will recover to normal operation automatically when the ovp or otp fault is removed. soft start / enable the aat1401 is enabled by en/set pulled to high after power on with a certain delay time. internal soft start circuitry limits the input inrush current and eliminates output voltage overshoot. when enset is pulled low the aat1401 enters a low-power, non-switching state. the total input current during shutdown is less than 1a. an external diode limits v out to the level of v in during shut - down. the diode consumes a small amount of additional input current depending on the ovp resistor divider value. over-temperature protection thermal protection disables the aat1401 when internal dissipation becomes excessive. thermal protection dis - ables the power mosfet. the junction over-temperature threshold is 155c with 15c of temperature hysteresis. the output voltage automatically recovers when the over-temperature fault condition is removed. functional block diagram gnd pwm en/set comp in lx pgnd ovp osc ref interface control cs rset ovp downloaded from: http:///
10 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 over-voltage protection over-voltage protection prevents damage to the aat1401's lx pin during open-circuit or high output voltage condi - tions. an over-voltage event is defined as a condition where the voltage on the ovp pin exceeds the over-volt - age protection threshold (v ovp-t ). when v ovp has reached the threshold limit, the converter stops switching and the output voltage decays. switching resumes when the lower hysteresis limit of v ovp is reached, thereby maintaining an average output voltage between the upper and lower ovp thresholds. led current setting the maximum led current is determined by the r set resistor value. with a fixed 1.2v voltage on r set , the led maximum current is a linear ratio to the current flowing through r set . v set r set i led = 258 the led dimming is controlled via one of two options, either using the 32-step s 2 cwire single-wire interface via the en/set pin or pwm control with varied duty cycle up to 100khz frequency. 32 s 2 cwire rising-edge steps set the led current from 100% to 2% percentage of the maxi - mum led current value when pwm control is disabled by pulling the pwm pin high. s 2 cwire can also be used to set maximum led current along with a pwm signal to dim the led lighting from 100% to 1% of duty cycle. s 2 cwire? serial interface the led current magnitude can be controlled by the en/ set pin using the s 2 cwire interface. the interface records rising edges of the en/set pin and decodes them into 32 individual current level settings. code 1 is full scale (maximum led current), and code 32 is 2% of the full scale. the modulo 32 interface wraps states back to state 1 after the 32nd clock. the counter can be clocked at speeds up to 1mhz, so intermediate states are not visi - ble. the first rising edge of en/set enables the ic and initially sets the output led current to full scale after 500s t lat . once the final clock cycle is input for the desired brightness level, the en/set pin should be held high to maintain the device output current at the pro - grammed level. the device is disabled 500s after the en/set pin enters a logic low state. the en/set timing is designed to accommodate a wide range of data rates from 20khz to 1mhz. after the first rising edge of en/set, the boost converter is enabled and reaches full capacity after the soft-start time. exact counts of clock pulses for the desired current level should be entered on the en/set pin with a single burst of clocks. the counter refreshes each time a new clock input to the en/set pin is detected. a constant cur - rent is maintained as long as en/set remains in a logic high state. to save power, the boost converter is switched off after en/set has remained in the low state for at least the t off timeout period as shown in figure 1. s 2 cwire serial interface timing 1 en/set 2 n- 1 n 3 2 data reg 0n 0 t hi t lo t lat t off figure 1: s 2 cwire timing diagram. downloaded from: http:///
11 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 application informationled current setting the maximum led current is determined by value of the external resistor r set from 10ma to 31ma. the value of r set is determined by the voltage of r set and the led current, and can be calculated by: v set 258 i led r set = where v set = 1.2v. table 1 lists examples of standard 1% metal film r set values for different maximum led current requirements. maximum led current (ma) r set (k) 31 10 20 15 15 20 12 25 10 30 table 1: examples of standard 1% r set values for setting maximum led current levels. led current dimming is controlled either via the s 2 cwire single-wire interface through the en/set pin in 32 steps or via pwm control with varied duty cycle up to 100khz frequency. the s 2 cwire interface programs the led cur - rent from the maximum led current set by r set to 2% of the maximum led current as shown in table 2. s 2 cwire data led current (% i max ) s 2 cwire data led current (% i max ) 1 100 17 48 2 97 18 45 3 94 19 42 4 90 20 39 5 87 21 35 6 84 22 32 7 81 23 29 8 77 24 26 9 74 25 23 10 71 26 19 11 68 27 16 12 65 28 13 13 61 29 10 14 58 30 6 15 55 31 3 16 52 32 2 table 2: s 2 cwire dimming control current settings. figure 2 illustrates the led current value at different s 2 cwire code settings when r set is 15k with a maxi - mum led current of 20ma. i led (ma) 13 57 91 11 31 51 71 92 12 32 52 72 93 1 24 68 10 12 14 16 18 20 22 24 26 28 30 32 0 2 4 6 8 10 12 14 16 18 20 22 figure 2: s 2 cwire dimming control at maximum led current (20ma max). filtered pwm dimming the aat1401 provides a pwm input as an additional means of providing dimming control for cabc applica - tions. the led current reduces percentage linearly as the duty cycle decreasing. frequencies of up to 100khz can be applied. to avoid output flicker and noise, the input control pwm frequency is filtered by the low pass filter composed of the error amplifier and the external compensation capacitor. figure 3 shows the led current dimming controlled by varying the pwm duty cycle at r set = 15k. i led (ma) pwm duty cycle (%) 100 90 80 70 60 50 40 30 20 10 0 0 2 4 6 8 10 12 14 16 18 20 figure 3: filtered pwm dimming duty cycle vs. maximum led current (20ma max). downloaded from: http:///
12 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 capacitor selection a compensation capacitor c com is used for step-up con - verter loop compensation, soft startup time control, and pwm digital signal filtering. loop compensation requires matching values for c com , c out , i led , and v out : i led 30 10 -6 v out c out c com < the aat1401 can drive up to 6 white leds with forward voltages up to 4v each. in a worst case with v f of 4v, a c out value of 0.1f, and led maximum current of 20ma, the value of c com should be higher than 3.6nf. c out 30 v out i led 0.1 30 24 20 c com > (nf) = (nf) = 3.6nf a higher value for c com lengthens the soft startup time. the relationship between c com and startup time is almost linear, with startup time x 10 5 magnification of c com ; thus 56nf c com leads to a soft startup time of 5.6ms. table 3 gives several examples of minimum c com values at differ - ent c out and i led and the step-up converter's operation stable. values of 56nf for c com and 0.1f for c out are suitable in most cases. i led (ma) c out (f) v out (v) c com_min (nf) 31 0.1 24 2.3 31 1 24 23 20 0.1 24 3.6 20 1 24 36 10 0.1 24 7.2 10 1 24 72 table 3: minimum c com values vs. i led and c out (step-up converter operation stable). 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 as input, output and compen - sation capacitors in the aat1401 step-up converter led driver application. mlc capacitors of type x7r or x5r are recommended to ensure good capacitance stability over the full operating temperature range. a 4.7f/6.3v input capacitor is recommended and a 0.1f/50v output capac - itor is suitable as noted above. table 4 lists some recom - mended capacitors for use with the aat1401. inductor selection inductor value, saturation current and dcr is most impor - tant parameter in selecting an inductor for aat1401. the suitable inductance range for the aat1401 is 4.7h to 22h. higher inductance lowers the step-up convert - er's rms current value. together with lower dcr value of the inductor, it makes the total inductor power loss become much lower. considering inductor size and cost, 10h inductance is most suitable. figure 4 illustrates aat1401 efficiency at different inductance with similar dcr value. efficiency (%) i led (ma) 24 06 81 01 21 41 61 82 02 22 42 62 83 03 2 30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 4.7h10h 22h figure 4: aat1401 efficiency at different inductance with similar dcr (v in = 3.6v). manufacturer part number value (f) voltage (v) temperature range case size murata grm188r60j475k 4.7 6.3 x5r 0603 grm188r71h104ka93 0.1 50 x7r 0603 table 4: examples of aat1401 input and output capacitor selection. downloaded from: http:///
13 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 manufacturer part number inductance (h) maximum dc i sat current (ma) dcr (m, typ) size (mm) lxwxh type sumida cdrh3d18-100 10 900 164 4.0x4.0x2.0 shielded cdrh3d23-220 22 550 219 3.9x3.9x2.5 shielded murata lqh44pn100mp0l 10 1150 160 4.0x4.0x1.65 non-shielded lqh44pn220mp0l 22 800 370 4.0x4.0x1.65 non-shielded coilcraft epl2014-103mlc 10 600 440 2.1x2.2x1.0 shielded lps4012-223mlc 22 790 600 4.1x4.1x1.2 shielded coiltronics sd18-100-r 10 982 158 5.8x5.8x1.8 shielded table 5 : example of aat1401 inductor selection. considering the inductor copper loss, the inductor dcr value together with the rms current value flowing through the inductor leads to inductor conduction loss and also affects total efficiency. larger dcr leads to larger conduction loss and decreases total efficiency. the inductor conduction loss can be estimated as shown in the equation: 13 p l_loss = i 2 l_rms dcr = (i 2 l_max + i 2 l_min + i l_max i l_min ) dcr i l_max and i l_min are the inductor peak current and mini - mum current. figure 5 shows dcr effects on efficiency with a 10h inductor. efficiency (%) i led (ma) 24 06 81 01 21 41 61 82 02 22 42 62 83 03 2 30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 10h dcr 235m 3.2x3.2x1.55mm 10h dcr164m 4.0x4.0x2.0mm 10h dcr 36m 8.3x8.3x3.0mm figure 5: inductor dcr effects on total efficiency with 10h at 3.6v v in . inductor saturation current is also a key parameter in selecting an inductor. for the step-up converter, the peak inductor current is the dc input current plus half the inductor peak-to-peak current ripple. dc input current: v out i led v in i in = inductor peak-to-peak current ripple: v in (v out - v in ) v out l f i l_pp = inductor peak current: v in (v out - v in ) 2 v out l f v out i led v in i l _ pp 2 i l_peak = i in + = + for example, for a white led with 3.2v v f and 20ma current at 82% efficiency, the inductor peak current is 3.6 (3.2 6 - 3.6) 2 3.2 6 10 1m 3.2 6 0.02 3.6 0.82 i l_peak = + = 276ma table 5 gives some examples of recommended inductors for use with the aat1401. ovp setting over-voltage protection is designed to protect the step-up converter from a led string open fault. the ovp threshold is 1.2v. for 6 white leds with v f up to 4v, the resistor divider values for r1 and r2 can be calculated by: v out v ovp_th r 1 = - 1 r 2 higher resistor divider values decrease the power loss on the resistors. the total resistor value for 24v v out should be less than 2.4m for better noise immunity. values of 1m for resistor r1 and 51k for resistor r2 are recom - mended. downloaded from: http:///
14 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 manufacturer part number maximum dc blocking voltage v r (v) maximum dc forward current i f (ma) non-repetitive peak forward surge current i fsm (a) forward voltage v f (v) case size wxlxh (mm) diodes sdm20u40 40 250 1.0 0.37@20ma sod523 0.9x1.7x0.65 sd103bw 30 350 1.5 0.37@20ma sod123 1.7x3.85x1.35 central cmdsh2-3 30 200 1.0 0.32@15ma sdd323 1.35x2.6x1.0 tsc ss13l 30 1100 30 0.51@0.5a sub sma 1.9x3.8x1.43 ss14l 40 1100 30 0.51@0.5a sub sma 1.9x3.8x1.43 table 6: example of typical rectifier diode. rectifier diode selection an external rectifier diode is required for the non-syn - chronous step-up converter. a low v f schottky diode is recommended. the diode voltage rating should be higher than the ovp voltage. for an aat1401 driving 6 white leds with up to 4v forward voltage, the diode voltage rating should be higher than 24v. select a diode with dc rated current equal to the input current to allow an ade - quate margin for safe use. printed circuit board layout recommendations for best performance of the aat1401, the following guidelines should be followed when designing the pcb layout: 1. make the power trace as short and wide as possible, including the input/output power lines and switching node, etc. 2. make sure the ground bump connected to the print - ed circuit board with large copper area for better thermal dissipation. 3. put the input and output capacitor close to the ic as close as possible to get the best filter result. downloaded from: http:///
15 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 schematic and layout s 2 cwire/pwm microcontroller aat1401 white led driver c in 4.7f l1 10h 1m r1 51k r2 c out 0.1f/50v ds1 sdm20u40 dc+ dc- j2 pwm c com 56nf r set 15k vin r351k r451k c10.1f r71k r81k r91k r51k r6 51k v_ mcu en/set s 2 c up down cycle pic12f675 vdd 1 gp5 2 gp4 3 gp3 4 gp2 5 gp1 6 gp0 7 vss 8 u2 led1red j1 vin pgnd b1 lx a1 gnd c1 cs d1 rset d2 pwm b3 comp c3 in a2 en/set a3 ovp d3 aat1401iuq u1 1 2 3 j3 vmcu pwm d1 d2 d3 d4 d6 d5 figure 6: aat1401 evaluation board schematic. downloaded from: http:///
16 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 figure 7: aat1401 evaluation board figure 8: aat1401 evaluation board top side layout. top side layout (detail). figure 9: aat1401 evaluation board bottom side layout. downloaded from: http:///
17 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 component part number description manufacturer u1 aat1401 high eficiency serial led driver for 6 white leds skyworks u2 pic12f675 8-pin flash-based 8-bit cmos microcontroller microchip r1 rc0603fr-071ml res 1m 1/10w 1% 0603 smd yageo r2, r3, r4, r6 rc0603fr-0751kl res 51k 1/10w 1% 0603 smd rset rc0603fr-0715kl res 15k 1/10w 1% 0603 smd r5, r7, r8, r9 rc0603fr-071kl res 1k 1/10w 1% 0603 smd c in grm188r60j475k cap ceramic 4.7f 0603 x5r 6.3v 10% murata c out grm188r71h104k cap ceramic 0.1f 0603 x7r 50v 10% c1 grm188r71c104k cap ceramic 0.1f 0603 x7r 16v 10% c com grm188r71c563k cap ceramic 0.056f 0603 x7r 16v 10% d1, d2, d3, d4, d5, d6 rs-0805uw 20ma white led 0805 realstar ds1 sdm20u40 surface mount schottky barrier diode diodes l1 cdrh3d18-100nc power inductor 10h 0.9a smd sumida led1 0805krct red led 0805 hb cycle, up, down 6*6*5 12v 50ma pushbutton e-lt table 7: aat1401 evaluation board bill of materials (bom). downloaded from: http:///
18 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 1. yy = date code. 2. sample stock is generally held on part numbers listed in bold . ordering information package maximum # of leds interface marking 1 part number (tape and reel) 2 wlcsp-10 6 s 2 c, filtered pwm f4yy AAT1401IUQ-T1 skyworks green? products are compliant with all applicable legislation and are halogen-free. for additional information, refer to skyworks de?nition of green? , document number sq04-0074. package information wlcsp-10 1.145 0.035 0.800 bsc 0.265 0.015 1.545 0.035 0.200 bsc 1.200 bsc 0.400 bsc ? 0.2 (ref.) pin a1 indication line_1 line_2 0.100 0.100 0.300 0.300 0.380 0.025 0.200 0.025 0.070 0.035 bottom view top view end view 0.650 0.085 side view all dimensions in millimeters. downloaded from: http:///
19 aat1401 da ta sheet serial led driver with filtered pwm and 32-step s2c dimming control skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202113a ? skyworks proprietary information ? products and product information are subject to change without notice. ? june 27, 2012 copyright ? 2012 skyworks solutions, inc. all rights reserved. information in this document is provided in connection with skyworks solutions, inc. (skyworks) pr oducts or services. these materials, including the information contained herein, are provided by sky works as a service to its customers and may be used for informational purposes only by the customer. skyworks a ssumes no responsibility for errors or omissions in these materials or the information contained her ein. sky- works may change its documentation, products, services, speciications or product descriptions at any time, without notice. skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for conlicts, incompatibilities, or other dificulties arising from any fut ure changes. no license, whether express, implied, by estoppel or otherwise, is granted to any intellectual prope rty rights by this document. skyworks assumes no liability for any materials, products or informatio n provided here- under, including the sale, distribution, reproduction or use of skyworks products, information or ma terials, except as may be provided in skyworks terms and conditions of sale. the materials, products and information are provided as is without warranty of any kind, whether e xpress, implied, statutory, or otherwise, including fitness for a particular purpose or use, merchantability, performance, quality or non-infringement of any intellectual proper ty right; all such warranties are hereby expressly disclaimed. skyworks does not warrant the accuracy or completeness of the information, text, graphics or other items contained within these materials. skyworks shall not be liable for any damages, in- cluding but not limited to any special, indirect, incidental, statutory, or consequential damages, i ncluding without limitation, lost revenues or lost profits that may result from the use of the materials or information, whether or not the recipient of materials has been advised of the possibility of such damage. skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, o r other equipment in which the failure of the skyworks products could lead to personal injury, death , physical or en- vironmental damage. skyworks customers using or selling skyworks products for use in such applicatio ns do so at their own risk and agree to fully indemnify skyworks for any damages resulting from such improper use or sale. customers are responsible for their products and applications using skyworks products, which may dev iate from published speciications as a result of design defects, errors, or operation of products ou tside of pub- lished parameters or design speciications. customers should include design and operating safeguards to minimize these and other risks. skyworks assumes no liability for applications assistance, custom er product design, or damage to any equipment resulting from the use of skyworks products outside of stated pub lished speciications or parameters. skyworks, the skyworks symbol, and breakthrough simplicity are trademarks or registered trademarks of skyworks solutions, inc., in the united states and other countries. third-party brands and names are for identiication purposes only, and are the property of their respective owners. additional information , including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by refere nce. downloaded from: http:///

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