july 2005 1 m9999-070105 mic2287 micrel, inc. mic2287 1 .2mhz pwm white led driver with ovp in 2mm 2mm mlf? and thin sot-23 general description the mic2287 is a 1.2mhz pulse width modulated (pwm), boost-switching regulator that is optimized for constant- current, white led driver applications. with a maximum output voltage of 34v and a switch current of over 500ma, the mic2287 easily drives a string of up to 8 white leds in series, ensuring uniform brightness and eliminating several ballast resistors. the mic2287 implements a constant frequency, 1.2mhz pwm control scheme. the high frequency pwm operation saves board space by reducing external component sizes. the added bene?t of the constant frequency pwm scheme as opposed to variable frequency topologies is much lower noise and input ripple injected back to the battery source. to optimize ef?ciency, the feedback voltage is set to only 95mv. this reduces the power dissipation in the current set resistor and allows the lowest total output voltage, hence minimal current draw from the battery. the mic2287 is available with 3 levels of overvoltage protec- tion, 15v, 24v, and 34v. this allows designers to choose the smallest possible external components with the appropriate voltage ratings for their applications. the mic2287 is available in low pro?le thin sot-23 5-lead and an 8-lead 2mm 2mm mlf? package options. the mic2287 has a junction temperature range of C40c to +125c. all support documentation can be found on micrels web site at www.micrel.com. typical application 10h 0.22f 6.3? 95mv 1-cellli ion 1f 2 3 1 4 5 mic2287bd5 vinen sw fb gnd cmdsh-3 3-series white led driver in thin sot-23 features ? 2.5v to 10v input voltage ? output voltage up to 34v ? over 500ma switch current ? 1.2 mhz pwm operation ? 95mv feedback voltage ? output overvoltage protection (ovp) ? options for 15v, 24v, and 34v ovp ? <1% line and load regulation ? <1a shutdown current ? over-temperature protection ? uvlo ? low pro?le thin sot-23-5 package option ? 8-lead 2mm 2mm mlf? package option ? C40c to +125c junction temperature range applications ? white led driver for backlighting: - cell phones - pdas - gps systems - digital cameras - mp3 players - ip phones ? photo ?ash led driver ? led ?ashlights ? constant current power supplies micrel, inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408 ) 474-1000 ? http://www.micrel.com mlf and micro leadframe are trademarks of amkor technology, inc. 10h 0.22f 1f 1-cell li ion 6.3? mic2287-34bml vinen sw ovp fb gnd 95mv cmdsh-3 6-series white led driver with output ovp in 2mm 2mm mlf?-8 downloaded from: http:///
mic2287 micrel, inc. m9999-070105 2 july 2005 pin description pin number pin number tsot-23-5 2mm 2mm mlf? pin name pin function 1 7 sw switch node (input): internal power bipolar collector. 2 gnd ground (return): ground. 3 6 fb feedback (input): output voltage sense node. connect the cathode of the led to this pin. a resistor from this pin to ground sets the led current. 4 3 en enable (input): logic high enables regulator. logic low shuts down regula- tor. 5 2 vin supply (input): 2.5v to 10v for internal circuitry. 1 ovp overvoltage protection (input): connect to the output. 4 agnd analog ground. 8 pgnd power ground. 5 nc no connect (no internal connection to die). ep gnd ground (return): exposed backside pad. pin con?guration fb gnd en vin sw 3 1 5 2 4 tsot-23-5 (bd5) out vin en gnd gndsw fb nc 12 3 4 87 6 5 ep 8-pin mlf? (bml) (top view) fused lead frame ordering information marking overvoltage junction part number code protection temp. range package lead finish mic2287bd5 sgaa n/a C40c to 125c thin sot-23-5 standard mic2287yd5 sgaa n/a C40c to 125c thin sot-23-5 lead free mic2287-15bml sla 15v C40c to 125c 2mm x 2mm mlf? standard mic2287-15yml sla 15v C40c to 125c 2mm x 2mm mlf? lead free mic2287-24bml slb 24v C40c to 125c 2mm x 2mm mlf? standard mic2287-24yml slb 24v C40c to 125c 2mm x 2mm mlf? lead free mic2287-34bml slc 34v C40c to 125c 2mm x 2mm mlf? standard mic2287-34yml slc 34v C40c to 125c 2mm x 2mm mlf? lead free downloaded from: http:///
july 2005 3 m9999-070105 mic2287 micrel, inc. absolute maximum ratings (1) supply voltage (v in ) ..................................................... 12v switch voltage (v sw ) ......................................C0.3v to 34v enable pin voltage (v en ) ................................... C0.3 to v in fb voltage (v fb ) ............................................................. 6v switch current (i sw ) ........................................................ 2a ambient storage temperature (t s ) .......... C65c to +150c esd rating (3) ............................................................... 2kv operating ratings (2) supply voltage (v in ) ..........................................2.5v to 10v junction temperature range (t j ) ............ C40c to +125c package thermal impedance 2mm 2mmmlf? ( ja ) ..................................... 93c/w thin sot-23-5 ( ja ) ......................................... 256c/w electrical characteristics (4) t a = 25c, v in = v en = 3.6v, v out = 10v, i out = 10ma, unless otherwise noted. bold values indicate C40c t j 125c. symbol parameter condition min typ max units v in supply voltage range 2.5 10 v v uvlo under voltage lockout 1.8 2.1 2.4 v i vin quiescent current v fb > 200mv, (not switching) 2.5 5 ma i sd shutdown current v en = 0v (5) 0.1 1 a v fb feedback voltage (5%) 90 95 100 mv i fb feedback input current v fb = 95mv C450 na line regulation (6) 3v v in 5v 0.5 1 % load regulation (6) 5ma i out 20ma 0.5 2 % d max maximum duty cycle 85 90 % i sw switch current limit 750 ma v sw switch saturation voltage i sw = 0.5a 450 mv i sw switch leakage current v en = 0v, v sw = 10v 0.01 5 a v en enable threshold turn on 1.5 v turn off 0.4 v i en enable pin current v en = 10v 20 40 a f sw oscillator frequency 1.05 1.2 1.35 mhz v ovp overvoltage protection mic2287bml- 15 only 13 14 16 v mic2287bml- 24 only 21 22.5 24 v mic2287bml- 34 only 30 32 34 v t j overtemperature 150 c threshold shutdown hysteresis 10 c notes:1. absolute maximum ratings indicate limits beyond which damage to the component may occur. electrical speci?cations do not apply when operating the device outside of its operating ratings. the maximum allowable power dissipation is a function o f the maximum junction temperature, t j (max), the junction-to-ambient thermal resistance, ja , and the ambient temperature, t a . the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 2. this device is not guaranteed to operate beyond its speci?ed operating ratings. 3. devices are inherently esd sensitive. handling precautions required. human body model. 4. speci?cation for packaged product only. 5. i sd = i vin . 6. guaranteed by design. downloaded from: http:///
mic2287 micrel, inc. m9999-070105 4 july 2005 typical characteristics 90 91 92 93 94 95 96 97 98 99 100 0 2 4 6 8 10 12 fb voltage (mv) v in (v) feedback voltage vs. input voltage 0 1 2 3 4 5 0 2 4 6 8 10 12 shutdown current (a) v in (v) shutdown current vs. input voltage 0 1 2 3 4 5 0 2 4 6 8 10 12 quiescent current (ma) v in (v) quiescent current vs. input voltage 70 72 74 76 78 80 82 84 efficiency (% ) i out (ma) 3 series led efficiency l = 10h c out = 0.22f v in = 4.2v v in = 3.6v v in = 3.0v 0 5 10 15 20 25 70 72 74 76 78 80 82 84 efficiency (% ) i out (ma) 6 series led efficiency l = 10h c out = 0.22f v in = 4.2v v in = 3.6v v in = 3.0v 0 5 10 15 20 25 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -40 0 40 80 120 switching frequency (mhz) temperature (c) switch frequency vs. temperature 0 5 10 15 20 25 30 35 40 45 50 -50 0 50 100 ienable (a) temperature (c) en pin bias currency vs. temperature i en = 4.2v i en = 3.6v i en = 3.0v i en = 10v 300 350 400 450 500 550 -40 0 40 80 120 saturation vol t age (mv) temperature (c) saturation voltage vs. temperature i sw = 500ma 600 650 700 750 800 850 900 -40 0 40 80 120 current limit (ma) temperature (c) current limit vs. temperature v in = 2.5 v 0 100 200 300 400 500 600 0 100 200 300 400 500 saturation vol t age (mv) i sw (ma) switch saturation voltage vs. current v in = 2.5v v in = 5v downloaded from: http:///
july 2005 5 m9999-070105 mic2287 micrel, inc. functional description the mic2287 is a constant frequency, pwm current mode boost regulator. the block diagram is shown above. the mic2287 is composed of an oscillator, slope compensation ramp generator, current ampli?er, g m error ampli?er, pwm generator, and a 500ma bipolar output transistor. the oscil- lator generates a 1.2mhz clock. the clocks two functions are to trigger the pwm generator that turns on the output transistor and to reset the slope compensation ramp genera- tor. the current ampli?er is used to measure the switch cur- rent by amplifying the voltage signal from the internal sense resistor. the output of the current ampli?er is summed with the output of the slope compensation ramp generator. this summed current-loop signal is fed to one of the inputs of the pwm generator. functional diagram gnd v ref pwm generator ramp generator 1.2mhz oscillator sw en fb ovp* vin 95mv * ovp available on mlf tm package option only g m ovp* s mic2287 block diagram the g m error ampli?er measures the led current through the external sense resistor and ampli?es the error between the detected signal and the 95mv reference voltage. the output of the g m error ampli?er provides the voltage-loop signal that is fed to the other input of the pwm generator. when the current-loop signal exceeds the voltage-loop signal, the pwm generator turns off the bipolar output transistor. the next clock period initiates the next switching cycle, maintain- ing the constant frequency current-mode pwm control. the led is set by the feedback resistor: i led = 95mv r fb the enable pin shuts down the output switching and disables control circuitry to reduce input current-to-leakage levels. enable pin input current is zero at zero volts. downloaded from: http:///
mic2287 micrel, inc. m9999-070105 6 july 2005 external component selection the mic2287 can be used across a wide rage of applications. the table below shows recommended inductor and output capacitor values for various series-led applications. series leds l manufacturer min c out manufacturer 2 22h lqh32cn220k21 (murata) 2.2f 0805zd225kat(avx) nlc453232t-220k(tdk) grm40x5r225k10(murata) 15h lqh32cn150k21 (murata) 1f 0805zd105kat(avx) nlc453232t-150k(tdk) grm40x5r105k10(murata) 10h lqh32cn100k21 (murata) 0.22f 0805zd224kat(avx) nlc453232t-100k(tdk) grm40x5r224k10(murata) 6.8h lqh32cn6r8k21 (murata) 0.22f 0805zd225kat(avx) nlc453232t-6r8k(tdk) grm40x5r225k10(murata) 4.7h lqh32cn4r7k21 (murata) 0.22f 0805zd224kat(avx) nlc453232t-4r7k(tdk) grm40x5r224k10(murata) 3 22h lqh43mn220k21 (murata) 2.2f 0805yd225mat(avx) nlc453232t-220k(tdk) grm40x5r225k16(murata) 15h lqh43mn 150k21 (murata) 1f 0805yd105mat(avx) nlc453232t-150k(tdk) grm40x5r105k16(murata) 10h lqh43mn 100k21 (murata) 0.22f 0805yd224mat(avx) nlc453232t-100k(tdk) grm40x5r224k16(murata) 6.8h lqh43mn 6r8k21 (murata) 0.22f 0805yd224mat(avx) nlc453232t-6r8k(tdk) grm40x5r224k16(murata) 4.7h lqh43mn 4r7k21 (murata) 0.27f 0805yd274mat(avx) nlc453232t-4r7k(tdk) grm40x5r224k16(murata) 4 22h lqh43mn220k21 (murata) 1f 0805yd105mat(avx) nlc453232t-220k(tdk) grm40x5r105k25(murata) 15h lqh43mn 150k21 (murata) 1f 0805yd105mat(avx) nlc453232t-150k(tdk) grm40x5r105k25(murata) 10h lqh43mn 100k21 (murata) 0.27f 0805yd274mat(avx) nlc453232t-100k(tdk) grm40x5r274k25(murata) 6.8h lqh43mn 6r8k21 (murata) 0.27f 0805yd274mat(avx) nlc453232t-6r8k(tdk) grm40x5r274k25(murata) 4.7h lqh43mn 4r7k21 (murata) 0.27f 0805yd274mat(avx) nlc453232t-4r7k(tdk) grm40x5r274k25(murata) 5, 6 22h lqh43mn220k21 (murata) 0.22f 08053d224mat(avx) nlc453232t-220k(tdk) grm40x5r224k25(murata) 15h lqh43mn 150k21 (murata) 0.22f 08053d224mat(avx) nlc453232t-150k(tdk) grm40x5r224k25(murata) 10h lqh43mn 100k21 (murata) 0.27f 08053d274mat(avx) nlc453232t-100k(tdk) grm40x5r274k25(murata) 6.8h lqh43mn 6r8k21 (murata) 0.27f 08053d274mat(avx) nlc453232t-6r8k(tdk) grm40x5r274k25(murata) 4.7h lqh43mn 4r7k21 (murata) 0.27f 08053d274mat(avx) nlc453232t-4r7k(tdk) grm40x5r274k25(murata) 7, 8 22h lqh43mn220k21 (murata) 0.22f 08053d224mat(avx) nlc453232t-220k(tdk) grm40x5r224k25(murata) 15h lqh43mn 150k21 (murata) 0.22f 08053d224mat(avx) nlc453232t-150k(tdk) grm40x5r224k25(murata) 10h lqh43mn 100k21 (murata) 0.27f 08053d274mat(avx) nlc453232t-100k(tdk) grm40x5r274k25(murata) 6.8h lqh43mn 6r8k21 (murata) 0.27f 08053d274mat(avx) nlc453232t-6r8k(tdk) grm40x5r274k25(murata) 4.7h lqh43mn 4r7k21 (murata) 0.27f 08053d274mat(avx) nlc453232t-4r7k(tdk) grm40x5r274k25(murata) downloaded from: http:///
july 2005 7 m9999-070105 mic2287 micrel, inc. dimming control there are two techniques for dimming control. one is pwm dimming, and the other is continuous dimming. 1. pwm dimming control is implemented by applying a pwm signal on en pin as shown in figure 1. the mic2287 is turned on and off by the pwm signal. with this method, the leds operate with either zero or full current. the average led current is increas ed proportionally to the duty-cycle of the pwm signal. this technique has high-ef?ciency because the ic and the leds consume no current during the off cycle of the pwm signal. typical pwm frequency should be between 100hz and 10khz. 2. continuous dimming control is implemented by applying a dc control voltage to the fb pin of the mic2287 through a series resistor as shown in figure 2. the led intensity (current) can be dy- namically varied applying a dc voltage to the fb pin. the dc voltage can come from a dac signal, or a ?ltered pwm signal. the advantage of this ap- proach is a high frequency pwm signal (>10khz) that can be used to control led intensity. pwm vinen sw fb gnd v in figure 1. pwm dimming method vinen sw fb 5.11k 49.9k gnd dc v in equivalent figure 2. continuous dimming open-circuit protection if the leds are disconnected from the circuit, or in case an led fails open, the sense resistor will pull the fb pin to ground. this will cause the mic2287 to switch with a high duty-cycle, resulting in output overvoltage. this may cause the sw pin voltage to exceed its maximum voltage rating, possibly damaging the ic and the external components. to ensure the highest level of protection, the mic2287 has 3 product options in the 8-lead 2mm 2mm mlf? with over- voltage protection (ovp). the extra pins of the 8-lead 2mm 2mm mlf? package allow a dedicated ovp monitor with options for 15v, 24v, or 34v (see figure 3). the reason for the three ovp levels is to let users choose the suitable level of ovp for their application. for example, a 3-led application would typically see an output voltage of no more than 12v, so a 15v ovp option would offer a suitable level of protection. this allows the user to select the output diode and capacitor with the lowest voltage ratings, as well as smallest size and lowest cost. the ovp will clamp the output voltage to within the speci?ed limits. for the thin sot-23-5 package, an ovp pin is not available. an external zener diode can be connected from the output of the converter to fb pin as shown in figure 4. to implement similar protection. vinen gnd sw fb ovp v in figure 3. mlf? package ovp circuit vinen sw fb gnd v in 5.11k figure 4. thin sot-23 package ovp circuit start-up and inrush current during start-up, inrush current of approximately double the nominal current ?ows to set up the inductor current and the voltage on the output capacitor. if the inrush current needs to be limited, a soft-start circuit similar to figure 5 could be implemented. the soft-start capacitor, c ss , provides over- drive to the fb pin at start-up, resulting in gradual increase of switch duty cycle and limited inrush current. vinen sw fb c ss 2200pf r 10k gnd v in figure 5. soft-start circuit downloaded from: http:///
mic2287 micrel, inc. m9999-070105 8 july 2005 6-series led circuit without external soft-start time (100s/div.) enable (2v/div) input current (200ma/div) output vol t age l = 10h c in = 1f c out = 0.22f v in = 3.6v i out = 20ma 6 leds 6-series led circuit with external soft-start time (100s/div.) enable (2v/div) input current (200ma/div) output vol t age l = 10h c in = 1f c out = 0.22f v in = 3.6v i out = 20ma 6 ledsc ss = 2200pf r = 10kw downloaded from: http:///
july 2005 9 m9999-070105 mic2287 micrel, inc. package information 5-pin tsot (bd5) 8-pin mlf? (bml) downloaded from: http:///
mic2287 micrel, inc. m9999-070105 10 july 2005 recommended land pattern for mlf? 2 2 8 lead micrel inc. 2180 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 web http://www.micrel.com this information furnished by micrel in this data sheet is believed to be accurate and reliable. however no responsibility is assumed by micrel for its use. micrel reserves the right to change circuitry and speci?cations at any time without noti?cation to t he customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a signi?cant injury to the user. a purchaser's use or sale of micrel products for use in life support appliances, devices or systems is a purchaser's own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2004 micrel, inc. downloaded from: http:///
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