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MIC3291 1.2mhz pwm white led driver with internal schottky diode and single-wire linear brightness control mlf and micro lead frame are registered trademarks of amkor technologies, inc. micrel inc. ? 2180 fortune drive ? san jose, 408) 474-1000 ? http://www.micrel.com ca 95131 ? usa ? tel +1 ( 408 ) 944-0800 ? fax + 1 ( september 2010 m9999-092810 (408) 944-0800 general description the MIC3291 is a pwm switching boost regulator that is optimized for constant current white led (wled) driver applications. the MIC3291 features an internal schottky diode, allowing an efficient dc/dc solution that requires only four external components. the MIC3291 allows for a single-wire simple digital interface to control the dimmi ng over 16 steps with a linear scale. the preprogramming feature allows the user to select any one of the 16 wled current levels as the start up brightness level. the feedback voltage of the MIC3291 is only 250mv, allowing high efficiency while retaining excellent accuracy for the wled current. the MIC3291 implements a constant frequency 1.2mhz pwm control scheme. the high frequency pwm operation saves board space by reducing external component sizes. the 1.2mhz pwm scheme also reduces switching noise and ripple to the input power source. the 2.5v to 6.5v input voltage range of the MIC3291 allows direct operation from sing le cell li-ion as well as 3 to 4 cell nicad/nimh/alkaline batteries. battery life is preserved with a low 1a shutdown current. the MIC3291 is available in a low profile thin sot23 6- pin and 2mm 2mm mlf ? 8-pin packages with a junction temperature range of ?40 c to +125 c. data sheets and support documentation can be found on micrel?s web site at: www.micrel.com . features ? single wire combines 16 level linear brightness and shutdown control ? 18v / 25v ovp options supports up to four and six wleds ? startup in any one of 16 brightness levels ? internal schottky diode ? 2.5v to 6.5v input voltage ? 1.2mhz pwm operation ? over 500ma switch current ? 250mv reference voltage ? 5% led current accuracy ? <1a shutdown current ? uvlo and over-temperature protection ? thin sot23-6l package option ? 2mm 2mm leadless mlf ? package option ? ?40 o c to +125 o c junction temperature range applications ? mobile handsets ? lcd handset backlighting ? digital cameras ? portable media players/mp3 players ? portable applications __ _________________________________________________________________________________________________________ typical application white led driver with ovp and digital control
micrel, inc. MIC3291 september 2010 2 m9999-092810 (408) 944-0800 ordering information part number 1 marking code 4 output voltage over-voltage protection junction temperature range package 2,3 MIC3291-18yd6 w1 8f adjustable 18v ? 40c to + 125 c tsot23-6 MIC3291-25yd6 w2 5f adjustable 25v ? 40c to + 125 c tsot23-6 MIC3291-18yml fwa adjustable 18v ? 40c to + 125 c 2mm 2mm mlf ? MIC3291-25yml adjustable 25v ? 40c to + 125 c 2mm 2mm mlf ? fwb notes: 1. other options available. cont act micrel marketing for details. 2. mlf ? is a green rohs compliant package. lead fini sh is nipdau. mold compound is halogen free. 3. mlf ? = pin 1 identifier. 4. overbar ( )and underbar symbols ( _ ) may not be to scale. pin configuration 2mm 2mm 8-pin mlf ? (ml) (top view) tsot23-6 (d6) (top view) pin description pin number 8-pin mlf ? pin number sot23-6 pin name pin name 1 6 out output and over-voltage protection (output) 2 5 vin supply (input): 2.5v to 6.5v for internal circuitry. 3 4 dc single pin digital control. see diagrams. 4 ? gnd ground (return): ground. 5 ? nc no connect (no internal connection to die) 6 3 fb feedback (input): output voltage sense node. connect the cathode of the led to this pin. 7 1 sw switch node (input): inte rnal power bipolar collector. 8 2 gnd ground (return): ground. pad ? gnd ground (return): backside pad.
micrel, inc. MIC3291 september 2010 3 m9999-092810 (408) 944-0800 absolute maximum ratings (1) supply voltage (v in ) .................................................... 7.5v switch voltage (v sw ) ..................................... ?0.3v to 27v digital control voltage (v dc ) ..............................?0.3 to v in fb voltage (v fb )............................................................. 6v switch current (i sw )........................................................ 2a ambient storage temperature (t s )......... ?65 c to +150 c esd rating (2) ................................................................2kv operating ratings (3) supply voltage (v in ) ???????..?? ......2.5v to 6.5v output voltage (v out ) ?????.? ............... (v in to v ovp ) junction temperature range (t j ) ?? .... ? 40 c to +125 c package thermal impedance ja 2mm 2mm mlf ? -8l ................................. 93 c/w ja tsot23-6 .................................................. 235 c/w electrical characteristics (4) t a = + 25 o c, v in = 3.6v, v out = 10v, i out = 20ma, unless otherwise noted. bold values indicate ? 40c t j + 125c. symbol parameter condition min. typ. max. units v in supply voltage range 2.5 6.5 v v uvlo under-voltage lockout 1.8 2.1 2.4 v i vin quiescent current v fb >500mv 2 4 ma i sd shutdown current (dc pin low ) v dc = 0v for > 2ms. 0.01 1 a v fb feedback voltage ( 5%) 237 250 263 mv feedback input current v fb = 250mv 450 na line regulation 2.5v v in 4.5v 0.5 i fb load regulation 5ma i out 20ma 0.5 % d max maximum duty cycle 86 90 % i sw switch current limit v in = 3.6v 500 750 1200 ma v dc dc pin thresholds high low 1.1 0.4 v i dc dc pin current v dc = 3.6v 5 10 a t shutdown shutdown pulse width v in = 2.8v to 5.5v v dc = low 1260 s t mode_up count up mode pulse width v in = 2.8v to 5.5v v dc = low 100 160 s t mode_down count down mode pulse width v in = 2.8v to 5.5v v dc = low 420 500 s t start_up turn-on delay time v in = 2.8v to 5.5v 140 s t prog_low programming pulse width low v in = 2.8v to 5.5v 1 32 s t prog _ high programming pulse width high v in = 2.8v to 5.5v 1 32 s t delay minimum delay for mode change v in = 2.8v to 5.5v v dc = high 140 s t prog_setup first pulse window for preprogramming v in = 2.8v to 5.5v 35 50 s f sw oscillator frequency 1 1.2 1.35 mhz
micrel, inc. MIC3291 september 2010 4 m9999-092810 (408) 944-0800 electrical characteristics (4) (continued) t a = + 25 o c, v in = 3.6v, v out = 10v, i out = 20ma, unless otherwise noted. bold values indicate ? 40c t j + 125c. symbol parameter condition min. typ. max. units v d schottky forward drop i d = 150ma 0.8 1 v i rd schottky leakage current v r = 30v 4 a 3291- 18 only (nominal voltage) 15 16.5 18 v ovp over-voltage protection 3291- 25 only (nominal voltage) 22.1 23.5 25 v tj over-temperature threshold shutdown 150 c notes: 1. absolute maximum ratings indicate limits beyond which damage to the component may occur. electr ical specifications do not ap ply when operating the device outside of its operating ratings. the maximum allowabl e power dissipation is a function of the maximum junction temp erature, 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. ic devices are inherently esd sensitive. handling precautions required. hum an body m odel, 1.5k ? in series with 100pf. 3. this device is not guaranteed to oper ate beyond its specified operating rating. 4 . specification for packaged product only.
micrel, inc. MIC3291 september 2010 5 m9999-092810 (408) 944-0800 typical characteristics feedback voltage vs. brightness level 0 25 50 75 100 125 150 175 200 225 250 275 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 brightness level (0-15) feedback voltage (mv ) 6 series white led efficiency 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 white led current (ma) 3 series white led efficiency 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 white led current (ma) v in = 2.8v v in = 2.8v efficiency (%) l = 10h c out = 0.27f v in = 3.6v v in = 4.2v efficiency (%) l = 10h c out = 0.27f v in = 3.6v v in = 4.2v 6 series white led efficiency 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 white led current (ma) feedback voltage v s. input voltage 240 242 244 246 248 250 252 254 256 258 260 2.533.544.555.56 input voltage (v) 3 series white led efficiency 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 white led current (ma) efficiency (%) l = 22h c out = 0.27f v in = 2.8v v in = 4.2v feedback voltage (mv efficiency (%) v in = 3.6v l = 22h c out = 0.27f v in = 2.8v v in = 3.6v v in = 4.2v ) peak switch current v s. input voltage 200 300 400 500 600 700 800 900 1000 feedback voltage (mv current limit vs. input voltage 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 current limit (a) input current vs. input voltage 0 50 100 150 200 250 300 350 2.5 3 3.5 4 4.5 5 5.5 6 input voltage (v) input current (ma) l=10h 2.533.544.555.5 input voltage (v) ) 6 leds 3 leds 2.6 3.1 3.6 4.1 4.6 5.1 5.6 6.1 6.6 input voltage (v)
micrel, inc. MIC3291 functional characteristics september 2010 6 m9999-092810 (408) 944-0800
micrel, inc. MIC3291 september 2010 7 m9999-092810 (408) 944-0800 functional characteristics (continued)
micrel, inc. MIC3291 september 2010 8 m9999-092810 (408) 944-0800 functional diagram MIC3291 block diagram
micrel, inc. MIC3291 september 2010 9 m9999-092810 (408) 944-0800 functional description the MIC3291 is a constant frequency, pwm current mode boost led driver. it is composed of an oscillator, slope compensation ramp generator, current amplifier, g m error amplifier, pwm generator, bipolar output transistor, digital interface with d/a converter and schottky rectifier diode. it features true single-wire linear digital control that may be used to vary the brightness of the output leds. the oscillator generates a 1.2mhz clock which triggers the pwm generator that turns on the output transistor and resets the slope compensation ramp generator. the current amplifier is used to measure the switch current by amplifying the voltage signal from the internal sense resistor. the output of the current amplifier 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. MIC3291 block diagram the g m error amplifier measures the led current through the external sense resistor and amplifies the error between the detected signal and the reference voltage indicated by the digital interface. the output of the g m error amplifier 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, maintaining the constant frequency current mode pwm control. the led current level at maximum brightness is set by the feedback resistor: led r 250mv i led = MIC3291 digital interface the MIC3291 incorporates an easy to use single-wire, serial programming interface allowing users to set led brightness to one of sixteen levels spaced in a linear manner. in contrast to other solutions requiring a pwm drive signal to maintain led brightness, the MIC3291 is ?set and forget?, relieving the controlling processor of the constant burden of supplying a drive signal. additionally, brightness levels can be preset so that leds can be turned on at a particular brightness level. brightness level fb voltage (mv) 15 250 14 235 13 220 12 205 11 190 10 175 9 160 8 145 7 130 6 115 5 100 4 85 3 70 2 55 1 40 0 25 table 1. brightness level vs. ideal fb voltage startup presuming no presetting brightness command is issued (discussed in a later section), the MIC3291 will startup in its default state approximately 140s (t start_up ) after a logic level high has been applied and maintained at the dc pin. in the default state t he led drive current is at the maximum brightness level of 15 and brightness counter is set to count down mode. any falling edges during the t prog_setup period will cause the initial brightness level of the leds to be below the maximum brightness level. this is discussed in more detail in the presetting brightness section. figure 2. typical startup timing
micrel, inc. MIC3291 september 2010 10 m9999-092810 (408) 944-0800 shutdown whenever a logic level low is applied to the dc input pin for a period greater than or equal to t shutdown (1260s), the MIC3291 w ill be in power saving shutdown mode. figure 3. shutdown timing once the device is shutdown, the boost supply is disabled and the leds are turned off. brightness level information stored in the mi c3291 prior to shutdown will be lost. programming pulse counter modes at power up the MIC3291 defaults to count down mode. in count down mode, the brightness level is decreased one level by applying two programming pulses, as shown in figure 6. the counting mode can be changed to count up mode by pulling the dc pin low for a period equal to t mode_up (100s to 160s). the device will remain in count up mode until its state is changed to count down mode or by disabling the MIC3291. figure 4. mode change to count up to change the state back to count down mode, pull the dc pin low for a period equal to t mode_down (420s to 500s). now the internal circuitry will remain in count down mode until changed to count up mode as described previously. figure 5. mode change to count down programming the brightness level MIC3291 is designed to start driving the output leds (t start_up ) in 140s at the maximum brightness level of 15. after startup, the internal control logic is ready to decrease the led brightness upon receiving programming pulses (negative edges applied to dc pin). since MIC3291 starts in count down mode, the brightness level is decreased one level by applying two programming pulses, as shown in figure 6. each programming pulse has a high (t prog_high ) and a low (t prog_low ) pulse width that must be between 1s to 32s. note that n+1 number of pulses are needed to decrease brightness by n level(s) since the first clock pulse is ignored. ignoring the first clock pulse is necessary so mode change (t mode_up , t mode_down ) pulses do not result in adjustments to the brightness level. the MIC3291 internal circuit can be changed from count down mode to count up mode and vice versa. the user may elect to send a mode change as shown in figure 4 to set the MIC3291 to step up the brightness level with subsequent programming pulses. for proper operation, ensure the dc pin has remained high for at least t delay (140s) before issuing a mode change command. figure 6. brightness programming pulses multiple brightness levels can be changed together with multiple programming pulses, as shown in figure 7. when issuing multiple brightness level adjustment commands to the dc pin, ensure both t prog_low and t prog_high are within 1s and 32s.
micrel, inc. MIC3291 september 2010 11 m9999-092810 (408) 944-0800 to maintain operation at the current brightness level simply maintain a logic level high signal at the dc pin. figure 7. decreasing brightness several levels as mentioned, MIC3291 can be programmed to set led drive current to produce one of 16 distinct brightness levels. the internal logic keeps track of the brightness level with an up/down counter circuit. the counter rollover section explains how the brightness counter functions with continued programming edges. counter rollover the MIC3291 internal up/down counter contains registers from 0 to 15. when the brightness level is at 0 and a programming pulse forces the brightness to step down, then the counter will rollo ver to level 15. this is illustrated in figure 8. figure 8. down counter rollover similarly, when the counter mode is set to count up and a programming pulse forces the brightness level to step up from level 15, then the counter will rollover to level 0 as illustrated in figure 9. figure 9. up counter rollover one step brightness changes for applications where a keypad button press is to be translated into a brightness level change, the following method of decreasing the brightness level may be useful. this ?one step? brightness change procedure relieves the user from keeping track of the MIC3291?s up/down counter mode. it combines a counter mode change with a programming pulse, therefore a one step decrease in brightness is assured no matter what the previous up/down counter mode was. figure 10. one step brightness decrease this method is quite simple and the only requirement is that the first dc low period be equal to the t mode_down (420s to 500s) and immediately followed by a falling edge within t prog_high (1s to 32s) as shown in figure 10 for one step brightness decrease. similarly a one step increase can be assured by first generating a dc down pulse whose period is equal to the t mode_up (100s to 160s) and immediately followed by a falling edge within t prog_high (1s to 32s). figure 11 illustrates the proper timing for execution of a one step brightness increase.
micrel, inc. MIC3291 figure 12 shows the correct presetting sequence to set the MIC3291 brightness to level 6 prior to startup. the sequence is initiated by driving the dc pin low for a period exceeding t shutdown (1260s) to insure that the part has entered the power saving shutdown state erasing all brightness level state and mode setting. then the dc pin is driven high and the first presetting pulse edge is entered within the t prog_setup window. notice that when using the presetting feature the first programming pulse is not ignored. this is because the counter?s default mode is count down and a mode change cannot be performed in the presetting mode. (note that the same timi ng requirements of standard brightness programming also apply during presetting brightness.) figure 11. one step brightness increase presetting brightness the brightness level can be preset before the MIC3291 begins to drive the leds by sending a series of programming edges via the dc pin during the t start_up (140s) period and between 35s to 50s after the dc pin is first pulled high. the 15s timeframe between 35s and 50s is the t prog_setup period. the MIC3291 does not drive current into t he load until dc pin is kept high for t start_up (140s) after presetting has concluded in order to grant the user sufficient time to preset led brightness. the first presetting pulse edge must occur somewhere between the timeframe of 35s to 50s after dc pin is first pulled high otherwise the MIC3291 may continue to start at the full (default) brightness level. figure 12. preset timing september 2010 12 m9999-092810 (408) 944-0800
micrel, inc. MIC3291 september 2010 13 m9999-092810 (408) 944-0800 typical application circuit (MIC3291-xxyml) bill of materials item part number manufacturer description qty. c1 grm185r61a105ke36d murata (1) capacitor, 1f ceramic, 10v, x5r, size 0603 1 c2 grm21br71e474kco1l murata (1) capacitor, 0.47f ceramic, 25v, x7r, size 0805 1 r1 crcw060312r40frt1 vishay (2) 12.4 ? , 1%, 0603 1 l1 vls252010t-100m tdk (3) 10h, 650ma, 712m ? , l2.5mm x w2.0mm x h1.0mm 1 u1 MIC3291-xxyml micrel, inc. (4) 1.2mhz pwm boost led driver with single-wire linear digital control 1 notes: 1. murata: www.murata.com . 2. vishay: www.vishay.com . 3. tdk: www.tdk.com . 4. micrel, inc.: www.micrel.com .
micrel, inc. MIC3291 september 2010 14 m9999-092810 (408) 944-0800 typical application circuit (MIC3291-xxyd6) bill of materials item part number manufacturer description qty. c1 grm185r61a105ke36d murata (1) capacitor, 1f ceramic, 10v, x5r, size 0603 1 c2 grm21br71e474kco1l murata (1) capacitor, 0.47f ceramic, 25v, x7r, size 0805 1 r1 crcw060312r40frt1 vishay (2) 12.4 ? , 1%, 0603 1 l1 vls252010t-100m tdk (3) 10h, 650ma, 712m ? , l2.5mm x w2.0mm x h1.0mm 1 u1 MIC3291-xxyd6 micrel, inc. (4) 1.2mhz pwm boost led driver with single-wire linear digital control 1 notes: 1. murata: www.murata.com . 2. vishay: www.vishay.com . 3. tdk: www.tdk.com . 4. micrel, inc.: www.micrel.com .
micrel, inc. MIC3291 september 2010 15 m9999-092810 (408) 944-0800 pcb layout recommendations top layer bottom layer
micrel, inc. MIC3291 september 2010 16 m9999-092810 (408) 944-0800 package information 6-pin tsot23 (d6)
micrel, inc. MIC3291 september 2010 17 m9999-092810 (408) 944-0800 package information (continued) 8-pin mlf ? (ml) 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 the information furnished by micrel in this data sheet is belie ved to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specific ations at any time without notification to the customer. micrel products are not designed or authorized for use as components in life suppor t appliances, devices or systems where malfu nction of a product reasonably be expected to result in pers onal injury. life support devices or systems are devices or systems that (a) are intended for surgical impla into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significan t 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. can nt ? 2010 micrel, incorporated.

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