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aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 1 www.analogictech.com general description the aat1239-1 is a high frequency, high efficiency con- stant current boost converter capable of driving up to ten (10) series-connected white leds or 40v. it is an ideal power solutions for backlight applications with up to ten white leds in series. the input voltage is 2.7v to 5.5v for single-cell lithium-ion/polymer (li-ion) based portable devices. the led current is digitally controlled across a 6x oper- ating range using analogictech?s simple serial control? (s 2 cwire?) interface. programmability across 26 dis- crete current steps provides high resolution, low noise, flicker-free, constant led outputs. in programming aat1239 operation, led brightness increases based on the data applied at the en/set pin. the sel logic pin changes the feedback voltage between two program- mable ranges. the aat1239-1 features a high current limit and fast, stable transitions for stepped or pulsed current applica- tions. the high switching frequency (up to 2mhz) pro- vides fast response and allows the use of ultra-small external components, including chip inductors and capacitors. fully integrated control circuitry simplifies design and reduces total solution size. the aat1239-1 offers a true load disconnect feature which isolates the load from the power source while in the off or disabled state. this eliminates leakage current, making the devic- es ideally suited for battery-powered applications. the aat1239-1 is available in the pb-free, thermally- enhanced 12-pin tsopjw package. features ? input voltage range: 2.7v to 5.5v ? maximum continuous output 40v @ 30ma ? drives up to 10 leds in series ? constant led current with 3.5% accuracy over temperature and input voltage range ? digital control with s 2 cwire single wire interface ? 26 discrete steps ? no pwm control required ? no additional circuitry ? up to 82% efficiency ? up to 2mhz switching frequency allows small external chip inductor and capacitors ? hysteretic control ? no external compensation components ? excellent load transient response ? high efficiency at light loads ? integrated soft start with no external capacitor ? true load disconnect guarantees <1.0 a shutdown current ? selectable feedback voltage ranges for high resolution control of load current ? short-circuit, over-voltage, and over-temperature protection ? 12-pin tsopjw package ? -40c to +85c temperature range applications ? color display backlight ? digital still cameras (dscs) ? digital photo frames ? pdas and notebook pcs ? white led drivers typical application lin en/set pgnd pvin l1 2.2h c1 2.2f c2 2.2f m673 li-ion: v in = 2.7v to 4.2v aat1239-1 ds1 ss16l or equivalent r1 (r ballast ) 30 i led 20ma .1 sw fb sel vin agnd r3 12k r2 374k ovp enable/set feedback voltage select white leds osram lw m678 or equivalent
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 2 1239-1.2007.10.1.0 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 2 1239-1.2007.10.1.0 www.analogictech.com pin descriptions pin # symbol function 1 pvin input power pin; connected to the source of the p-channel mosfet. connect to the input capacitor(s). 2 en/set ic enable pin and s 2 cwire input control to set output current. 3 sel fb voltage range select. a logic low sets the fb voltage range from 0.4v to 0.1v; a logic high sets the fb voltage range from 0.6v to 0.3v. 4 vin input voltage for the converter. connect directly to the pvin pin. 5 n/c no connection. 6, 7 sw boost converter switching node. connect the power inductor between this pin and lin. 8 pgnd power ground for the boost converter. 9 agnd ground pin. 10 fb feedback pin. connect a resistor to ground to set the maximum led current. 11 ovp feedback pin for over-voltage protection sense. 12 lin switched power input. connect the power inductor between this pin and sw. pin configuration tsopjw-12 (top view) 1 2 3 4 5 6 12 11 10 9 8 7 pvin en/set sel vin n/c sw lin ovp fb agnd pgnd sw
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 3 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 3 www.analogictech.com part number descriptions part number sel polarity high low s 2 c feedback voltage programming aat1239itp-1 0.6v v fb 0.3v 0.4v v fb 0.1v see table 2 absolute maximum ratings 1 t a = 25c unless otherwise noted. symbol description value units pvin, vin input voltage -0.3 to 6.0 v sw switching node 45 v lin, en/set, sel, fb maximum rating v in + 0.3 v 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 thermal information symbol description value units ja thermal resistance 160 c/w p d maximum power dissipation 625 mw 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.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 4 1239-1.2007.10.1.0 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 4 1239-1.2007.10.1.0 www.analogictech.com electrical characteristics 1 t a = -40c to +85c unless otherwise noted. typical values are at 25c, v in = 3.6v. symbol description conditions min typ max units power supply pv in , v in input voltage range 2.7 5.5 v v out(max) maximum output voltage 40 v i q operating current sel = gnd, fb = 0.1v 70 a i shdn shutdown current en/set = gnd 1.0 a i out maximum continuous output current 2 2.7v < v in < 5.5v, v out = 40v 30 ma v linereg(fb) / v in line regulation v in = 2.7v to 5.5v, v fb = 0.6v 0.7 % r ds(on) l low side switch on resistance 135 m r ds(on) in input disconnect switch on resistance 180 m t ss soft-start time from enable to output regulation; v fb = 300mv 400 s v ovp over-voltage protection threshold v out rising 1.1 1.2 1.3 v over-voltage hysteresis v out falling 100 mv i limit n-channel current limit 2.5 a t sd t j thermal shutdown threshold 140 c t hys t j thermal shutdown hysteresis 15 c sel, en/set v sel(l) sel threshold low 0.4 v v sel(h) sel threshold high 1.4 v v en/set(l) enable threshold low 0.4 v v en/set(h) enable threshold high 1.4 v t en/set (lo) en/set low time v en/set < 0.6v 0.3 75 s t en/set(hi) en/set high time v en/set > 1.4v 75 s t off en/set off timeout v en/set < 0.6v 500 s t lat en/set latch timeout v en/set > 1.4v 500 s i en/set en/set input leakage v en/set = 5v v in = 5v -1 1 a aat1239-1 v fb fb pin regulation v in = 2.7v to 5.5v, sel = gnd, en/set = data16 0.085 0.1 1.115 v v in = 2.7v to 5.5v, sel = high, en/set = high 0.54 0.6 0.66 1. specification over the -40c to +85c operating temperature range is assured by design, characterization, and correlation wi th statistical process controls. 2. maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and thermal limitations.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 5 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 5 www.analogictech.com typical characteristics efficiency vs. led current (10 white leds; r ballast = 30.1 ) i led (ma) efficiency (%) 66 68 70 72 74 76 78 80 2 4 6 8 10 12 14 16 18 2 0 v in = 5v v in = 4.2v v in = 3.6v efficiency vs. led current (9 white leds; r ballast = 30.1 ) i led (ma) efficiency (%) 66 68 70 72 74 76 78 2 4 6 8 10 12 14 16 18 20 v in = 5v v in = 4.2v v in = 3.6v shutdown current vs. input voltage (en = gnd) input voltage (v) shutdown current (a) 0.0 0.2 0.4 0.6 0.8 1.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5. 5 -40c 85c 25c line transient (10 white leds; r ballast = 30.1 ) time (50s/div) input voltage (top) (v) output voltage (middle) (v) feedback voltage (bottom) (v) 32.8 33 33.2 0.58 0.6 0.62 4.2v 3.6v accuracy i led vs. input voltage (v fb = 0.6v; r ballast = 30.1 ) input voltage (v) accuracy i led (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.7 3.2 3.7 4.2 4.7 5.2 5. 7 -40c 25c 85c accuracy i led vs. temperature (v fb = 0.6v; r ballast = 30.1 ) temperature (c) accuracy i led (%) -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -40 -15 10 35 60 85
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 6 1239-1.2007.10.1.0 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 6 1239-1.2007.10.1.0 www.analogictech.com typical characteristics soft start (10 white leds; v fb = 0.6v) time (200s/div) feedback voltage (middle) (v) enablevoltage (top) (v) inductor current (bottom) (a) 0 0.2 0.4 0.6 0 1 2 0v 3.3v soft start (10 white leds; v fb = 0.3v) time (200s/div) feedback voltage (middle) (v) enablevoltage (top) (v) inductor current (bottom) (a) 0 0.2 0.4 0 1 2 0v 3.3v 0v shutdown (10 white leds; v fb = 0.6v) time (100s/div) enablevoltage (top) (v) feedback voltage (middle) (v) inductor current (bottom) (a) 0 0.2 0.4 0.6 0.0 0.5 3.3v 0v shutdown (10 leds; v fb = 0.3v) time (50s/div) enablevoltage (top) (v) feedback voltage (middle) (v) inductor current (bottom) (a) 0 0.2 0.4 0 0.5 3.3v 0v output ripple (10 white leds; v in = 3.6v; c out = 2.2f; i led = 13ma) time (200ns/div) v sw (20v/div) v out (ac coupled) (20mv/div) i l (500ma/div) output ripple (10 white leds; v in = 3.6v; c out = 2.2f; i led = 20ma) time (200ns/div) v sw (20v/div) v out (ac coupled) (20mv/div) i l (500ma/div)
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 7 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 7 www.analogictech.com typical characteristics transition of led current (10 white leds; sel = low; i led = 3ma to 13ma) time (50s/div) output voltage (top) (v) feedback voltage (bottom) (v) 28 30 32 34 0.0 0.1 0.2 0.3 0.4 transition of led current (10 white leds; sel = low; i led = 13ma to 6ma) time (50s/div) output voltage (top) (v) feedback voltage (bottom) (v) 30 32 34 0.0 0.1 0.2 0.3 0.4 input disconnect switch resistance vs. input voltage input voltage (v) r ds(on)in (m ) 140 160 180 200 220 240 260 280 300 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 120c 100c 85c 25c low side switch on resistance vs. input voltage input voltage (v) r ds(on)l (m ) 80 100 120 140 160 180 200 220 240 260 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 120c 100c 25c 85c en/set latch timeout vs. input voltage input voltage (v) en/set latch timeout (s) 100 150 200 250 300 350 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c en/set off timeout vs. input voltage input voltage (v) en/set off timeout (s) 50 100 150 200 250 300 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25c 85c -40c
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 8 1239-1.2007.10.1.0 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 8 1239-1.2007.10.1.0 www.analogictech.com typical characteristics enable high threshold (v ih ) vs. input voltage input voltage (v) enable high threshold (v ih ) (v) 0.6 0.7 0.8 0.9 1.0 1.1 1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 25c 85c -40c enable low threshold (v il ) vs. input voltage input voltage (v) enable low threshold (v il ) (v) 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5. 5 25c 85c -40c
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 9 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 9 www.analogictech.com functional description the aat1239-1 consists of a dc/dc boost controller, an integrated slew rate controlled input disconnect mosfet switch, and a high voltage mosfet power switch. a high voltage rectifier, power inductor, output capacitor, and sense resistors are required to implement a dc/dc con- stant current boost converter. the input disconnect switch is activated when a valid input voltage is present and the en/set pin is pulled high. the slew rate control on the p-channel mosfet ensures minimal inrush cur- rent as the output voltage is charged to the input volt- age, prior to the switching of the n-channel power mosfet. monotonic turn-on is guaranteed by the inte- grated soft-start circuitry. soft-start eliminates output voltage overshoot across the full input voltage range and all loading conditions. the maximum current through the led string is set by the ballast resistor and the feedback voltage of the ic. the output current may be programmed by adjusting the level of the feedback reference voltage which is pro- grammed through the s 2 cwire interface. the sel pin selects one of two feedback voltage ranges. in the aat1239-1, the sel function is inverted in that the fb pin voltage can be programmed from 0.4v to 0.1v with a logic low applied to the sel pin and 0.6v to 0.3v with a logic high applied to the sel pin. the feedback volt- age can be set to any one of 16 current levels within each fb range, providing high-resolution control of the led current, using the single-wire s 2 cwire control. for some applications requiring a short duration of boosting current applying a low-to-high transition on the aat1239-1?s sel pin, led current can be programmed up to 3x. the step size is determined by the programmed voltage at the fb pin where the internal default setting is 1.5x in the aat1239-1. control loop the aat1239-1 provides the benefits of current mode control with a simple hysteretic output current loop pro- viding exceptional stability and fast response with mini- mal design effort. the device maintains exceptional constant current regulation, transient response, and cycle-by-cycle current limit without additional compen- sation components. the aat1239-1 modulates the power mosfet switching current to maintain the programmed fb voltage. this allows the fb voltage loop to directly program the functional block diagram control reference output select fb sel en/set pvin lin sw agnd pgnd ovp vin
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 10 1239-1.2007.10.1.0 www.analogictech.com required inductor current in order to maintain the desired led current. the switching cycle initiates when the n-channel mosfet is turned on and current ramps up in the inductor. the on interval is terminated when the inductor current reaches the programmed peak current level. during the off interval, the input current decays until the lower threshold, or zero inductor current, is reached. the lower current is equal to the peak current minus a preset hys- teresis threshold, which determines the inductor ripple current. the peak current is adjusted by the controller until the led output current requirement is met. the magnitude of the feedback error signal determines the average input current. therefore, the aat1239-1 controller implements a programmed current source connected to the output capacitor, parallel with the led string and ballast resistor. there is no right-half plane zero, and loop stability is achieved with no additional compensation components. an increase in the feedback voltage (v fb ) results in an increased error signal sensed across the ballast resistor (r1). the controller responds by increasing the peak inductor current, resulting in higher average current in the inductor and led string(s). alternatively, when the v fb is reduced, the controller responds by decreasing the peak inductor current, resulting in lower average current in the inductor and led string(s). under light load conditions, the inductor off interval current goes below zero and the boost converter enters discontinuous mode operation. further reduction in the load current results in a corresponding reduction in the switching frequency. the aat1239-1 provides pulsed frequency operation which reduces switching losses and maintains high efficiency under light load conditions. operating frequency varies with changes in the input volt- age, output voltage, and inductor size. once the boost converter has reached continuous mode, further increases in the led current will not significantly change the operat- ing frequency. a small 2.2 h (20%) inductor is selected to maintain high frequency switching (up to 2mhz) and high efficiency operation for outputs up to 40v. soft start / enable the input disconnect switch is activated when a valid input voltage is present and the en/set pin is pulled high. the slew rate control on the p-channel mosfet ensures minimal inrush current as the output voltage is charged to the input voltage, prior to switching of the n-channel power mosfet. monotonic turn-on is guaran- teed by the built-in soft-start circuitry. soft start elimi- nates output current overshoot across the full input volt- age range and all loading conditions. after the soft start sequence has terminated, the initial led current is determined by the internal, default fb voltage across the external ballast resistor at the fb pin. additionally, the aat1239-1 has been designed to offer the system designer two choices for the default fb volt- age based on the state of the sel pin. changing the led current from its initial default setting is easy by using the s 2 cwire single wire serial interface; the fb voltage can be decreased (as in the aat1239-1; see table 2) relative to the default fb voltage. current limit and over-temperature protection the switching of the n-channel mosfet terminates when a current limit of 2.5a (typical) is exceeded. this mini- mizes power dissipation and component stresses under overload and short-circuit conditions. switching resumes when the current decays below the current limit. thermal protection disables the aat1239-1 when inter- nal dissipation becomes excessive. thermal protection disables both mosfets. the junction over-temperature threshold is 140c with 15c of temperature hysteresis. the output voltage automatically recovers when the over-temperature fault condition is removed. over-voltage protection over-voltage protection prevents damage to the aat1239-1 during open-circuit or high output voltage conditions. an over-voltage event is defined as a condi- tion where the voltage on the ovp pin exceeds the over- voltage threshold limit (v ovp = 1.2v typical). when the voltage on the ovp pin has reached the threshold limit, the converter stops switching and the output voltage decays. switching resumes when the voltage on the ovp pin drops below the lower hysteresis limit, main- taining an average output voltage between the upper and lower ovp thresholds multiplied by the resistor divider scaling factor. under-voltage lockout internal bias of all circuits is controlled via the vin input. under-voltage lockout (uvlo) guarantees sufficient v in bias and proper operation of all internal circuitry prior to soft start.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 11 www.analogictech.com application information over-voltage protection ovp protection with open circuit failure the ovp protection circuit consists of a resistor network tied from the output voltage to the ovp pin (see figure 1). to protect the device from open circuit failure, the resistor divider can be selected such that the over-volt- age threshold occurs prior to the output reaching 40v (v out(max) ). the value of r3 should be selected from 10k to 20k to minimize losses without degrading noise immunity. r 2 = r 3 - 1 v out(max) v ovp ?? ?? r2 r3 c out vout aat1239-1 ovp gnd figure 1: over-voltage protection circuit. time (4ms/div) over voltage protection pin (top) (v) inductor current (bottom)(a) output voltage (middle) (v) 1.142v 1.238v 30 40 0 2 4 figure 2: over-voltage protection open circuit response (no led). assume r3 = 12k and v out(max) = 40v. selecting 1% resistor for high accuracy, this results in r2 = 374k (rounded to the nearest standard value). the minimum ovp threshold can be calculated: ?? + 1 ?? v out(ovp_min) = v ovp(min) = 35.4v r 2 r 3 to avoid ovp detection and subsequent reduction in the programmed output current (see following section), the maximum operating voltage should not exceed the minimum ovp set point. v out(max) < v out(ovp_min) in some cases, this may disallow configurations with high led forward voltage (v fled ) and/or greater than ten series white leds. v fled unit-to-unit tolerance can be as high as +15% of nominal for white led devices. ovp constant voltage operation under closed loop constant current conditions, the out- put voltage is determined by the operating current, led forward voltage characteristics (v fled ), quantity of series connected leds (n), and the feedback pin voltage (v fb ). v out = v fb + n v fled when the rising ovp threshold is exceeded, switching is stopped and the output voltage decays. switching auto- matically restarts when the output drops below the lower ovp hysteresis voltage (100mv typical) and, as a result, the output voltage increases. the cycle repeats, maintaining an average dc output voltage proportional to the average of the rising and falling ovp levels (mul- tiplied by the resistor divider scaling factor). high oper- ating frequency and small output voltage ripple ensure dc current and negligible flicker in the led string(s). the waveform in figure 3 shows the output voltage and led current at cold temperature with a ten series white led string and v ovp = 40v. as shown, the output voltage rises as a result of the increased v fled which triggers the ovp constant voltage operation. self heating of the leds triggers a smooth transition back to constant cur- rent control.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 12 1239-1.2007.10.1.0 www.analogictech.com v out (5v/div) i led (200ma/div) self-recovery cold temperature apply over-voltage protection figure 3: over-voltage protection constant voltage operation (10 white leds; i led = 20ma; r 2 = 12k ; r 3 = 374k ). while ovp is active, the maximum led current program- ming error ( i led ) is proportional to voltage error across an individual led ( v fled ). (n v fled(typ) - v out(ovp _ min) - v fb ) n v fled = to minimize the i led error, the minimum ovp voltage (v out(ovp_min) ) may be increased, yielding a corresponding increase in the maximum ovp voltage (v out(ovp_max) ). measurements should confirm that the maximum switch- ing node voltage (v sw(max) ) is less than 45v under worst- case operating conditions. ?? + 1 + v f + v ring ?? v sw(max) = v ovp(max) r 3 r 2 v f = -schottky diode ds1 forward voltage at turn-off v ring = voltage ring occurring at turn-off led selection and current setting the aat1239-1 is well suited for driving white leds with constant current. applications include main and sub-lcd display backlighting, and color leds. the led current is controlled by the fb voltage and the ballast resistor. for maximum accuracy, a 1% tolerance resistor is recommended. the ballast resistor (r ballast ) value can be calculated as follows: v fb(max) i led(max) r ballast = where: v fb(max) = 0.4v when sel = low v fb(max) = 0.6v when sel = high i.e., for a maximum led current of 20ma (sel = high): v fb i led(max) 0.6 0.020 r ballast = = = 30 30.1 maximum i led current (ma) r ballast ( ) sel = high sel = low 30 20.0 13.3 25 24.3 16.2 20 30.1 20.0 15 40.2 26.7 10 60.4 40.2 5 121.0 80.6 table 1: maximum led current and r ballast resistor values (1% resistor tolerance). typical white leds are driven at maximum continuous currents of 15ma to 20ma. the maximum number of series connected leds is determined by the minimum ovp voltage of the boost converter (v out(ovp_min) ), minus the maximum feedback voltage (v fb(max) ) divided by the maximum led forward voltage (v fled(max) ). v fled(max) can be estimated from the manufacturers? datasheet at the maximum led operating current. ?? + 1 ?? v out(ovp_min) = v ovp(typ) r 2 r 3 (v out(ovp_min) - v fb(max) ) v fled(max) n = figure 4 shows the schematic of using ten leds in series. assume v fled @ 20ma = 3.5v (typical) from lw m673 (osram) datasheet. ?? + 1 ?? v out(ovp_min) = 1.2v = 38.6v 374k 10.4k 38.6v - 0.6v 3.5v n = 10.9 therefore, under these typical operating conditions, ten leds can be used in series.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 13 www.analogictech.com led brightness control the aat1239-1 uses s 2 cwire programming to control led brightness and does not require pwm (pulse width modulation) or additional control circuitry. this feature greatly reduces the burden on a microcontroller or sys- tem ic to manage led or display brightness, allowing the user to ?set it and forget it.? with its high-speed serial interface (1mhz data rate), the output current of the aat1239-1 can be changed successively to brighten or dim the leds in smooth transitions (i.e., to fade out) or in abrupt steps, giving the user complete program- mability and real-time control of led brightness. 0 5 10 15 20 25 14710131 6 s 2 cwire data register led current (ma) sel=high sel=low default figure 5: programming aat1239-1 led current with r ballast = 30.1 . c1 2.2f 2.2h l1 374k r2 12k r3 r1 30.1 v cc 1 2 3 enable jp1 10k r4 2.2f c2 1 2 3 select jp2 ds1 under 20v application: c2 25v 0805 x7r 2.2f grm21br71e225ka73l c1 10v 0603 x5r 2.2f grm188r60j225ke01d ds1 ss16l n/c 5 vin 1 sw 6 pgnd 8 en 2 sel 3 sw 7 vp 4 gnd 9 fb 10 ovp 11 lin 12 aat1239-1 tsop12jw u1 led d1 led d2 led d3 led d4 led d5 led d9 l1 2.2h sd3814-2r2 or sd3110-2r2 led d6 led d7 led d8 led d10 c2 50v 1206 x7r 2.2f grm31cr71h225ka88 other alternatives: more stability at 40v: c2 50v 1206 x7r 4.7f grm31cr71h475k d1-d10 lw m673 white led figure 4: aat1239-1 white led boost converter schematic.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 14 1239-1.2007.10.1.0 www.analogictech.com alternatively, toggling the sel logic pin from low to high implements stepped or pulsed led currents by increas- ing the fb pin voltage. figure 6 illustrates the select pin scaling factor, defined as the led current with sel=high divided by the led current with sel=low. in the aat1239-1, the possible scaling factors are 3.0x to 1.5x with the internal default setting of 1.5x. s 2 cwire data register select pin scaling factor (low to high) (default) 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5 14 7101316 figure 6: aat1239-1 sel pin scaling factor: i led (sel = high) divided by i led (sel = low). s 2 cwire serial interface analogictech?s s 2 cwire single wire serial interface is a proprietary high-speed single-wire interface available only from analogictech. the s 2 cwire interface records rising edges of the en/set input and decodes them into 16 individual states. each state corresponds to a refer- ence feedback voltage setting on the fb pin, as shown in table 2. s 2 cwire serial interface timing the s 2 cwire single wire serial interface data can be clocked-in at speeds up to 1mhz. after data has been submitted, en/set is held high to latch the data for a period t lat . the fb pin voltage is subsequently changed to the level as defined by the state of the sel logic pin. when en/set is set low for a time greater than t off , the aat1239-1 is disabled. when the aat1239-1 is disabled, the register is reset to its default value. in the aat1239-1, the fb pin voltage is set to 0.3v if the en/set pin is subsequently pulled high. s 2 cwire feedback voltage programming the fb pin voltage is set to the default level at initial powerup. the aat1239-1 is programmed through the s2cwire interface. table 2 illustrates fb pin voltage pro- gramming for the aat1239-1. the rising clock edges applied at the en/set pin determine the fb pin voltage. if a logic low is applied at the sel pin of the aat1239-1, the default feedback voltage range becomes 0.4v to 0.1v and 0.6v to 0.3v for a logic high condition at the sel pin. 1 en/set 2 n-1 n 16 data reg 0n-1 0 t hi t lo t lat t off figure 7: aat1239-1 s 2 cwire timing diagram to program the output voltage.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 15 www.analogictech.com selecting the schottky diode to ensure minimum forward voltage drop and no recov- ery, high voltage schottky diodes are considered the best choice for the aat1239-1 boost converter. the out- put diode is sized to maintain acceptable efficiency and reasonable operating junction temperature under full load operating conditions. forward voltage (v f ) and package thermal resistance ( ja ) are the dominant fac- tors to consider in selecting a diode. the diode non- repetitive peak forward surge current rating (i fsm ) should be considered for high pulsed load applications, such as camera flash. i fsm rating drops with increasing conduc- tion period. manufacturers? datasheets should be con- sulted to verify reliability under peak loading conditions. the diode?s published current rating may not reflect actual operating conditions and should be used only as a comparative measure between similarly rated devices. 40v rated schottky diodes are recommended for outputs less than 30v, while 60v rated schottky diodes are rec- ommended for outputs greater than 35v. the switching period is divided between on and off time intervals. = t on + t off 1 f s during the on time, the n-channel power mosfet is conducting and storing energy in the boost inductor. during the off time, the n-channel power mosfet is not conducting. stored energy is transferred from the input battery and boost inductor to the output load through the output diode. duty cycle is defined as the on time divided by the total switching interval. t on t on + t off d = = t on ? f s rising clock edges/data register sel = low sel = high reference voltage (v) led current (ma); r ballast = 30.1 reference voltage (v) led current (ma); r ballast = 30.1 1 0.4 (default) 13.29 0.6 (default) 19.93 2 0.38 12.62 0.58 19.27 3 0.36 11.96 0.56 18.60 4 0.34 11.30 0.54 17.94 5 0.32 10.63 0.52 17.28 6 0.30 9.97 0.50 16.61 7 0.28 9.30 0.48 15.95 8 0.26 8.64 0.46 15.28 9 0.24 7.97 0.44 14.62 10 0.22 7.31 0.42 13.95 11 0.20 6.64 0.40 13.29 12 0.18 5.98 0.38 12.62 13 0.16 5.32 0.36 11.96 14 0.14 4.65 0.34 11.30 15 0.12 3.99 0.32 10.63 16 0.10 3.32 0.30 9.97 table 2: aat1239-1 s 2 cwire reference feedback voltage control settings with r ballast = 30.1 (assumes nominal values)*. *all table entries are preliminary and subject to change without notice.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 16 1239-1.2007.10.1.0 www.analogictech.com the maximum duty cycle can be estimated from the relationship for a continuous mode boost converter. maximum duty cycle (d max ) is the duty cycle at minimum input voltage (v in(min) ). v out - v in(min) v out d max = the average diode current is equal to the output current. i avg(tot) = i out the average output current multiplied by the forward diode voltage determines the loss of the output diode. p loss(diode) = i avg(tot) v f = i out v f for continuous led currents, the diode junction tem- perature can be estimated. t j(diode) = t amb + ja p loss(diode) output diode junction temperature should be maintained below 110oc, but may vary depending on application and/or system guidelines. the diode ja can be mini- mized with additional pcb area on the cathode. pcb heat-sinking the anode may degrade emi performance. the reverse leakage current of the rectifier must be con- sidered to maintain low quiescent (input) current and high efficiency under light load. the rectifier reverse cur- rent increases dramatically at elevated temperatures. selecting the boost inductor the aat1239-1 controller utilizes hysteretic control and the switching frequency varies with output load and input voltage. the value of the inductor determines the maximum switching frequency of the boost converter. increased output inductance decreases the switching frequency, resulting in higher peak currents and increased output voltage ripple. to maintain 2mhz maximum switching frequency and stable operation, an output inductor sized from 1.5 h to 2.7 h is recommended. a better estimate of d max is possible once v f is known. (v out + v f - v in(min) ) (v out + v f ) d max = where v f is the schottky diode forward voltage. if not known, it can be estimated at 0.5v. manufacturer?s specifications list both the inductor dc current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the satu- ration characteristics. measurements at full load and high ambient temperature should be completed to ensure that the inductor does not saturate or exhibit excessive temperature rise. manufacturer part number rated forward current (a) non-repetitive peak surge current (a) rated voltage (v) thermal resistance ( ja , c/w) size (mm) (lxwxh) case taiwan semiconductor co., ltd. ss16l 1.1 30 60 45 3.8x1.9x1.43 sub sma ss15l 30 50 45 3.8x1.9x1.43 sub sma ss14l 30 40 45 3.8x1.9x1.43 sub sma diodes, inc b340la 3 70.0 40 25 5.59x2.92x2.30 sma zetex zhcs350 0.35 4.2 40 330 1.7x0.9x0.8 sod523 table 3: typical surface mount schottky rectifiers for various output levels.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 17 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 17 www.analogictech.com the output inductor (l) is selected to avoid saturation at minimum input voltage, maximum output load condi- tions. peak current may be estimated using the follow- ing equation, assuming continuous conduction mode. worst-case peak current occurs at minimum input volt- age (maximum duty cycle) and maximum load. switching frequency (f s ) can be estimated from the curves and assumes a 2.2 h inductor. i out (1 - d max ) d max v in(min) (2 f s l) i peak = + at light load and low output voltage, the controller reduces the operating frequency to maintain maximum operating efficiency. as a result, further reduction in output load does not reduce the peak current. minimum peak current can be estimated from 0.5a to 0.75a. at high load and high output voltages, the switching fre- quency is somewhat diminished, resulting in higher i peak . bench measurements are recommended to confirm actu- al i peak and ensure that the inductor does not saturate at maximum led current and minimum input voltage. the rms current flowing through the boost inductor 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 manufacturer?s temperature rise, or thermal derating, guidelines. i peak i rms = 3 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 inductor?s operating temperature. p loss(inductor) = i rms 2 dcr to ensure high reliability, the inductor case temperature should not exceed 100oc. in some cases, pcb heatsink- ing applied to the lin node (non-switching) can improve the inductor?s thermal capability. pcb heatsinking may degrade emi performance when applied to the sw node (switching) of the aat1239-1. shielded inductors provide decreased emi and may be required in noise sensitive applications. unshielded chip inductors provide significant space savings at a reduced cost compared to shielded (wound and gapped) induc- tors. in general, chip-type inductors have increased winding resistance (dcr) when compared to shielded, wound varieties. inductor efficiency considerations the efficiency for different inductors is shown in figure 8 for ten white leds in series. smaller inductors yield increased dcr and reduced operating efficiency. 63 66 69 72 75 25811141720 led current (ma) efficiency (%) cdrh5d16f-2r2 (29m ) sd3814-2r2 (77m ) figure 8: aat1239-1 efficiency for different inductor types (v in = 3.6v; ten white leds in series). manufacturer part number inductance ( h) maximum dc i sat current (ma) dcr (m ) size (mm) lxwxh type sumida www.sumida.com cdrh2d14-2r2 2.2 1500 75 3.2x3.2x1.55 shielded cooper electronics www.cooperet.com sd3814-2r2 2.2 1900 77 4.0x4.0x1.0 shielded sd3110-2r2 2.2 910 161 3.1x3.1x1.0 shielded taiyo yuden www.t-yuden.com np03sb-2r0m 2 1900 32 4.0x4.0x1.8 shielded nr3010t-2r2m 2.2 1100 95 3.0x3.0x1.0 shielded table 4: recommended inductors for various output levels (select i peak < i sat ).
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 18 1239-1.2007.10.1.0 www.analogictech.com selecting the boost capacitors the high output ripple inherent in the boost converter necessitates low impedance output 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 aat1239-1 boost regulator. mlc capacitors of type x7r or x5r are recommended to ensure good capacitance stability over the full operating temperature range. the output capacitor is sized to maintain the output load without significant voltage droop ( v out ) during the power switch on interval, when the output diode is not conducting. a ceramic output capacitor from 2.2 f to 4.7 f is recommended (see table 5). typically, 50v rated capacitors are required for the 40v maximum boost output. ceramic capacitors sized as small as 0805 or 1206 are available which meet these requirements. mlc capacitors exhibit significant capacitance reduction with applied voltage. output ripple measurements should confirm that output voltage droop and operating stability are acceptable. voltage derating can minimize this fac- tor, but results may vary with package size and among specific manufacturers. output capacitor size can be estimated at a switching frequency (f s ) of 500khz (worst case). i out d max f s v out c out = to maintain stable operation at full load, the output capacitor should be sized to maintain v out between 100mv and 200mv. the boost converter input current flows during both on and off switching intervals. the input ripple current is less than the output ripple and, as a result, less input capacitance is required. pcb layout guidelines boost converter performance can be adversely affected by poor layout. possible impact includes high input and output voltage ripple, poor emi performance, and reduced operating efficiency. every attempt should be made to optimize the layout in order to minimize para- sitic pcb effects (stray resistance, capacitance, and inductance) and emi coupling from the high frequency sw node. a suggested pcb layout for the aat1239-1 boost converter is shown in figures 9 and 10. the follow- ing pcb layout guidelines should be considered: 1. minimize the distance from capacitor c1 and c2 negative terminal to the pgnd pins. this is espe- cially true with output capacitor c2, which conducts high ripple current from the output diode back to the pgnd pins. 2. minimize the distance between l1 to ds1 and switch- ing pin sw; minimize the size of the pcb area con- nected to the sw pin. 3. maintain a ground plane and connect to the ic pgnd pin(s) as well as the gnd terminals of c1 and c2. 4. consider additional pcb area on ds1 cathode to maximize heatsinking capability. this may be neces- sary when using a diode with a high v f and/or ther- mal resistance. 5. to avoid problems at startup, add a 10k resistor between the vin, vp and en/set pins (r4). this is critical in applications requiring immunity from input noise during ?hot plug? events, e.g. when plugged into an active usb port. manufacturer part number value ( f) voltage rating temp co case size murata grm188r60j225ke19 2.2 6.3 x5r 0603 murata grm188r61a225ke34 2.2 10 x5r 0603 murata grm21br71e225ka73l 2.2 25 x7r 0805 murata grm31cr71h225ka88 2.2 50 x7r 1206 murata grm31cr71h475k 4.7 50 x7r 1206 table 5: recommended ceramic capacitors.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 19 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 19 www.analogictech.com figure 9: aat1239-1 evaluation figure 10: aat1239-1 evaluation board top side layout (with ten leds board bottom side layout (with ten leds and microcontroller). and microcontroller). u1 aat1239-1 c1 2. 2f vin 1 en 2 lin ovp 12 11 sel 3 vp 4 5 n/c 6 sw fb gnd pgnd sw 10 9 8 7 vcc jp1 123 dc+ dc- l1 2.2h r3 12k r2 374k ds1 schottky c 10f c2 2.2f vout 30.1 r1 d1 wled d2 wled d3 wled d4 wled d5 wled d7 wled d8 wled d9 wled d10 wled u2 pic12f675 vdd 1 gp5 2 3 gp4 4 gp3 vss gp0 gp1 gp2 8 7 6 5 jp2 jp3 r4 10k c3 0.1f r9 330 d11 green r6 1k r5 1k r7 1k vcc r8 330 d12 red up down select aat1239-1 white led driver s 2 cwire microcontroller d6 wled jp4 s1 s2 s3 figure 11: aat1239-1 evaluation board schematic (with ten leds and microcontroller).
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 20 1239-1.2007.10.1.0 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 20 1239-1.2007.10.1.0 www.analogictech.com additional applications c1 2.2f pvin vin lin sw pgnd en/set sel ovp fb agnd l1 2.2h r3 12k r2 158k ds1 schottky c2 2.2f up to 17v/ 30ma max d1 led d2 led d3 led d4 led li-ion v in = 2.7v to 5.5v aat1239-1 r1 30.1 20ma efficiency vs. led current (4 white leds; r ballast = 30.1 ) i led (ma) efficiency (%) 74 75 76 77 78 79 80 81 82 83 84 2 4 6 8 10 12 14 16 18 2 0 v in = 5v v in = 4.2v v in = 3.6v figure 12: four leds in series configuration. c1 2.2f pvin vin lin sw pgnd en/set sel ovp fb agnd l1 2.2h r3 12k r2 287k ds1 schottky c2 2.2f up to 30v/ 30ma max d1 led d2 led d3 led d4 led li-ion v in = 2.7v to 5.5v aat1239-1 r1 30.1 20ma d5 led d6 led d7 led d8 led efficiency vs. led current (8 white leds; r ballast = 30.1 ) i led (ma) efficiency (%) 66 68 70 72 74 76 78 80 2 4 6 8 10 12 14 16 18 20 v in = 5v v in = 4.2v v in = 3.6v figure 13: eight leds in series configuration. c1 2.2f pvin vin lin sw pgnd en/set sel ovp fb agnd l1 2.2h r3 12k r2 324k ds1 schottky c2 2.2f up to 34v/ 30ma max d1 led d2 led d3 led d4 led li-ion v in = 2.7v to 5.5v aat1239-1 r1 30.1 20ma d5 led d6 led d7 led d8 led d9 led efficiency vs. led current (9 white leds; r ballast = 30.1 ) i led (ma) efficiency (%) 66 68 70 72 74 76 78 2 4 6 8 10 12 14 16 18 20 v in = 5v v in = 4.2v v in = 3.6v figure 14: nine leds in series configuration.
aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 21 www.analogictech.com aat1239-1 40v step-up converter for 4 to 10 white leds switchreg tm product datasheet 1239-1.2007.10.1.0 21 www.analogictech.com advanced analogic technologies, inc. 3230 scott boulevard, santa clara, ca 95054 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 speci cations or to discontinue any product or service without notice. except as provided in analogictech?s terms and conditions of sale, analogictech assumes no liability whatsoever, and analogictech disclaims any express or implied warranty re lating to the sale and/or use of analogictech products including liability or warranties relating to tness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right . in order to minimize risks associated with the customer?s applications, adequate 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 analogictech deems necessary to support this warranty. speci c testing of all parameters of each device is not necessarily performed. analogictech and the analogictech logo are trademarks of advanced analogic technologies incorporated. all other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders. ordering information package marking 1 part number (tape and reel) 2 tsopjw-12 zlxyy AAT1239ITP-1-T1 package information tsopjw-12 0.20 + 0.10 - 0.05 0.055 0.045 0.45 0.15 7 nom 4 4 3.00 0.10 2.40 0.10 2.85 0.20 0.50 bsc 0.50 bsc 0.50 bsc 0.50 bsc 0.50 bsc 0.15 0.05 0.9625 0.0375 1.00 + 0.10 - 0.065 0.04 ref 0.010 2.75 0.25 all dimensions in millimeters. 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold .

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