april 2010 1 m9999-042910 micrel, inc mic3287 mic3287 1 .2mhz pwm white led driver with ovp in thin sot-23 and 2mm x 2mm mfl ? general description the mic3287 is a 1.2mhz pulse width modulated (pwm) step-up switching regulator that is optimized for constant cur - rent white led driving applications. with a switch current of over 350ma, the mic3287-24 drives a string of up to 4 white leds in series, ensuring uniform brightness and eliminating several ballast resistors. the mic3287 implements a constant frequency 1.2mhz pwm current-mode control scheme. the high frequency pwm op - eration saves board space by reducing external component sizes. the added beneft of the constant frequency pwm control scheme as opposed to variable frequency control schemes is much lower noise and input ripple injected back to the battery source. to optimize effciency, the feedback voltage is set to only 250mv. the mic3287 is also available with a maximum 24v over-voltage protection. the mic3287 is available in low profle thin sot-23 5-pin and thin sot-23 6-pin packages. the mic3287 has a junc - tion 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 250mv 1-cell li ion 1f 2 3 1 4 5 mic3287yd5 vin en sw fb gnd 3-series white led driver in thin sot-23-5 features ? 2.8v to 6.5v input voltage ? 350ma switch current ? 1.2 mhz pwm operation ? 250mv feedback voltage ? optional 24v output over-voltage protection (ovp) ? up to 36v output voltage without ovp ? <1% line and load regulation ? <1a shutdown current ? over-temperature protection ? under-voltage lock out (uvlo) ? low profle thin sot-23-5 package option ? low profle thin sot-23-6 package option ? 8-pin 2mm x 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 ? led flashlights ? 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 microlead frame are registered trademarks of amkor technology, inc. 10h 0.22f 1f 1-cell li ion mic3287-24yd6 vin en sw ovp fb gnd 250mv 5 1 3 2 4 6 4-series white led driver with output ovp in thin sot-23-6
micrel, inc. mic3287 april 2010 2 m9999-042910 pin confguration fb gnd en vin sw 3 1 5 2 4 fb gnd en vin sw 3 1 6 2 4 5 ovp tsot -23-5 (yd5 ) tsot -23-6 (yd6 ) 1 vin ovp en agnd 8 pgnd sw fb nc 7 6 5 2 3 4 ep 8-pin 2mm x 2mm mlf? (yml) ordering information part number marking code overvoltage protection junction temp. range package lead finish mic3287yd5 wgaa n/a -40c to +125c thin sot-23-5 lead free mic3287-24yd6 whaa 24v -40c to +125c thin sot-23-6 lead free mic3287-24yml wla 24v -40c to +125c 8-pin 2mm x 2mm mlf lead free pin description pin number tsot-23-5 pin number tsot-23-6 pin number 8-pin mlf pin name pin function 1 1 7 sw switch node (input): internal power bipolar collector. 2 2 4 agnd analog ground (return): ground. 2 2 8 pgnd power ground (return): ground. 3 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 4 3 en enable (input): logic high enables regulator. logic low shuts down regu - lator. 5 6 1 vin supply (input): 2.8v to 6.5v for internal circuitry. 5 2 ovp overvoltage protection (input): connect to the output. 5 nc not connected ep ep exposed backside pad: connect to ground.
april 2010 3 m9999-042910 micrel, inc mic3287 absolute maximum ratings (1) supply voltage (v in ) ........................................................ 7v switch voltage (v sw ) ...................................... C0.3v to 40v enable pin voltage (v en ) ................................... C0.3 to v in fb voltage (v fb ) ............................................................. 6v switch current (i sw ) ..................................................... 1.2a ambient storage temperature (t s ) .......... C65c to +150c esd rating (3) ................................................................ 2kv operating ratings (2) supply voltage (v in ) ......................................... 2.8v to 6.5v output voltage (v out ) ......................................... v in to 36v output voltage (v out ) (4) ................................... v in to v ovp junction temperature range (t j ) ............ C40c to +125c package thermal impedance thin sot-23-5 ( ja ) (5) ....................................... 207c/w thin sot-23-6 ( ja ) (5) ....................................... 134c/w 8-pin mlf ( ja ) ................................................... 90c/w electrical characteristics (6) 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 2.8 6.5 v v uvlo under voltage lockout 1.8 2.1 2.4 v i vin quiescent current v fb > 500mv, (not switching) 2.1 5 ma i sd shutdown current v en = 0v (7) 0.04 1 a v fb feedback voltage (7.5%) 231 250 269 mv i fb feedback input current v fb = 250mv C450 na line regulation 3v v in 5v (8) 0.4 1 % load regulation 5ma i out 20ma (8) 0.5 % d max maximum duty cycle 85 90 % i sw switch current limit v in = 3.6v 350 ma v sw switch saturation voltage v in = 3.6v, i sw = 300ma 250 mv i sw switch leakage current v en = 0v, v sw = 10v 0.01 1 a v en enable threshold turn on 1.5 v turn off 0.4 v i en enable pin current v en = 10v 21 40 a f sw oscillator frequency 1 1.2 1.4 mhz v ovp overvoltage protection mic3287-24yd6 17 19 24 v mic3287-24yml 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 specifcations do not apply when operating the device outside of its operating ratings. the maximum allowable power dissipation is a function of 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 specifed operating ratings. 3. devices are inherently esd sensitive. handling precautions required. human body model. 4. for options with ovp. 5. using 4 layer pcb. 6. specifcation for packaged product only. 7. i sd = i vin . 8. guaranteed by design.
micrel, inc. mic3287 april 2010 4 m9999-042910 typical characteristics 45 50 55 60 65 70 75 80 85 246 81 01 21 41 61 82 0 efficiency (% ) white led current (ma) 3 series white led efficiency v in =3.2v v in =3.6v v in =4.2v l = 10h c out = 0.22f 45 50 55 60 65 70 75 80 85 246 81 01 21 41 61 82 0 efficiency (% ) white led current (ma) 4 series white led efficiency v in =3.2v v in =3.6v v in =4.2v l = 10h c out = 0.22f 0 2 4 6 8 10 12 -40 enable pin current (a) temperature (c) enable pin current vs. temperature -25 -10 5 20 35 50 65 80 v en =1.8v v en =2.5v v en =3.3v v en =5v 1.0 1.1 1.2 1.3 1.4 1.5 frequency (mhz) frequency vs. temperature -40 temperature (c) -25 -10 5 20 35 50 65 80 v in =3.2v v in =3.6v v in =4.2v 240 244 248 252 256 260 feedback voltage (mv) feedback voltage vs. temperature -40 temperature (c) -25 -10 5 20 35 50 65 80 v in =3.6v 248 249 250 251 252 253 254 2.8 feedback voltage (mv) input voltage (v) feedback voltage vs. input voltage 3.2 3.6 4.0 4.4 4.8 5.2 5.6 2.0 2.1 2.2 2.3 2.4 2.5 2.8 quiescent current (ma) quiescent current vs. input voltage input voltage (v) 3.2 3.6 4.0 4.4 4.8 5.2 5.6 600 650 700 750 800 850 900 current limit (ma) curremt limit vs. temperature -40 temperature (c) -25 -10 5 20 35 50 65 80 v in =3.6v 720 740 760 780 800 820 840 2.8 current limit (ma) current limit vs. input voltage input voltage (v) 3.2 3.6 4.0 4.4 4.8 5.2 5.6 0.001 0.002 0.003 2.8 shutdown current (ua) shutdown current vs. input voltage input voltage (v) 3.2 3.6 4.0 4.4 4.8 5.2 5.6
april 2010 5 m9999-042910 micrel, inc mic3287 functional description the mic3287 is a constant frequency pulse width modulated (pwm) current-mode step-up regulator. the block diagram is shown above. the mic3287 is composed of an oscillator, slope compensation ramp generator, current amplifer, g m er - ror amplifer, pwm generator, and a 350ma minimum bipolar output transistor. the oscillator 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 com - pensation ramp generator. the current amplifer is used to measure the switch current by amplifying the voltage signal from the internal sense resistor. the output of the current amplifer is summed with the output of the slope compensa - tion 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 250mv g m ovp v ref error amplifier current amplifier * ovp available on tsop-23-6 and mlf? package options onl y . mic3287 block diagram the g m error amplifer measures the led current through the external sense resistor and amplifes the error between the detected signal and the internal 250mv reference voltage. the output of the g m error amplifer 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, thus main - taining the constant frequency current-mode pwm control. the led current is set by the feedback resistor: i led = 250mv r fb the enable pin shuts down the internal power bipolar transistor and disables the control circuitry to reduce input current-to-leakage levels. enable pin input current is zero at zero volts.
micrel, inc. mic3287 april 2010 6 m9999-042910 external component selection the table below shows recommended inductor and output capacitor combinations for optimal performance. series leds l min c out 2 22h 2.2f 15h 1f 10h 0.22f 6.8h 0.22f 4.7h 0.22f 3 22h 2.2f 15h 1f 10h 0.22f 6.8h 0.22f 4.7h 0.27f 4 22h 1f 15h 1f 10h 0.22f 6.8h 0.27f 4.7h 0.27f
april 2010 7 m9999-042910 micrel, inc mic3287 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 to the en pin, as shown in figure 1. the mic3287 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 increased proportionally to the duty-cycle of the pwm signal. this technique has high-effciency because the ic and the leds consume no current during the off time 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 mic3287 through a series resistor, as shown in figure 2. the led intensity (current) can be dynamically varied with the applied dc control voltage. the dc voltage can come from a dac signal, or a fltered pwm signal. the advantage of the fltered pwm signal approach is a high frequency pwm signal (>10khz) can be used to control led intensity (current). pwm vin en sw fb gnd v in figure 1. pwm dimming method vin en sw fb 5.1 1k 49.9k gnd dc? equivalent v in figure 2. continuous dimming open-circuit protection if the leds are disconnected from the circuit, or in the case that an led fails, the sense resistor will then pull the fb pin to ground. this will cause the mic3287 to switch with a high duty- cycle, resulting in output over-voltage. this may cause the sw pin voltage to exceed its maximum voltage rating, damaging the ic and the external components. to ensure the highest level of protection, the mic3287 has buit-in 24v over-voltage protection functionality in the tsot-23-6 pin and 8-pin mlf? package options. the ovp will clamp the output voltage to within the specifed limits. start-up and inrush current if the inrush current needs to be limited, a soft-start circuit, simi - lar to figure 3, could be implemented. the soft-start capacitor, c ss , provides overdrive to the fb pin at start-up, resulting in gradual increase of switch duty cycle and limited in rush current. vin en sw fb c ss 2200pf r 10k gnd v in figure 3. soft-start circuit
micrel, inc. mic3287 april 2010 8 m9999-042910 package information 5-pin tsot (yd5) 6-pin tsot (yd6)
april 2010 9 m9999-042910 micrel, inc mic3287 micrel inc. 2180 fortune drive san jose, ca 95131 usa t e l + 1 (408) 944-0800 f a x + 1 (408) 474-1000 w e b 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 specifcations at any time without notifcation to the 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 signifcant 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. ? 2006 micrel, inc. 8-pin 2mm x 2mm mlf ? (ml)
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