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mic2846a high efficiency 6 channel linear wled driver with dam?, digi tal control and dual low i q ldos dam, dynamic average matching is a trademark of micrel, inc. mlf and micro leadframe are registered trademark amkor technology inc. micrel inc. 2180 fortune drive san jose, ca 95131 usa tel +1 ( 408 ) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com april 2010 m9999-041210-d general description the mic2846a is a high efficiency white led (wled) driver featuring two low quiescent current ldos. it is designed to drive up to six leds and greatly extend battery life for portable display backlighting and keypad backlighting in mobile device s. the mic2846a architecture provides the highest possible efficiency by eliminating switching losses present in traditional charge pumps or inductive boost circuits. with a typical dropout of 40mv at 20ma, the mic2846a allows the leds to be driven directly from the battery eliminating switching noise and losses present with the use of boost circuitry. the mic2846a features dynamic averaged matching? (dam?) which is specifically designed to get the optimum matching despite process variations. this ensures a typical matching of 1.5% between all six led channels. the led brightness is preset by an external resistor and can be dimmed using a single-wire digital control. the digital interface takes commands from digital programming pulses to change the brightness in a logarithmic scale similar to the eyes perception of brightness. the single- wire digital brightness control is divided into two modes of operation; full brightness mode or battery saving mode for a total of 49 brightness steps. the mic2846a also features two independently enabled low quiescent current ldos . each ldo offers 3% accuracy over temperature, low dropout voltage (150mv @ 150ma), and low ground current under all load conditions (typically 35a). both ldos can be turned off to draw virtually no current. the mic2846a is available in the 2.5mm x 2.5mm 14-pin thin mlf ? leadless package with a junction temperature range of -40 c to +125 c datasheet and support documentation can be found on micrels web site at: www.micrel.com. features w l e d d r i v e r ? high efficiency (no voltage boost losses) ? dynamic average matching? (dam?) ? single wire digital control ? input voltage range: 3.0v to 5.5v ? dropout of 40mv at 20ma ? matching better than 1.5% (typical) ? current accuracy better than 1.5% (typical) ? maintains proper regulation regardless of how many channels are utilized ldos ? very low ground current C typical 35a ? stable with 1f ceramic output capacitor ? dropout at 150mv at 150ma ? thermal shutdown and current limit protection ? available in a 2.5mm x 2.5mm 14-pin thin mlf ? package applications ? mobile handsets ? lcd handset backlighting ? handset keypad backlighting ? digital cameras ? portable media/mp3 players ? portable navigation devices (gps) ? portable applications downloaded from: http:///
micrel inc. mic2846a april 2010 2 m9999-041210-d typical application digital lcd display backlight with 6 wleds and camera module 6 digital high current flash driver downloaded from: http:///
micrel inc. mic2846a april 2010 3 m9999-041210-d ordering information (1,2,3) part number mark code ldo1 vout ldo2 vout temperature range package mic2846a-mfymt ypmf 2.8v 1.5v C40c to +125c 14-pin 2.5mm x 2.5mm tmlf ? mic2846a-mgymt ypmg 2.8v 1.8v C40c to +125c 14-pin 2.5mm x 2.5mm tmlf ? mic2846a-pgymt yppg 3.0v 1.8v C40c to +125c 14-pin 2.5mm x 2.5mm tmlf ? mic2846a-ppymt yppp 3.0v 3.0v C40c to +125c 14-pin 2.5mm x 2.5mm tmlf ? mic2846a-scymt ypsc 3.3v 1.0v C40c to +125c 14-pin 2.5mm x 2.5mm tmlf ? note: 1. thin mlf ? = pin 1 identifier. 2. thin mlf ? is a green rohs-compliant package. lead fini sh is nipdau. mold compound is halogen free. 3. contact micrel for other output voltages. pin configuration 14-pin 2.5mm x 2.5mm thin mlf ? (mt) (top view) pin description pin number pin name pin function 1 vin voltage input. connect at least 1f ceramic capacitor between vin and gnd. 2 ldo2 output of ldo2. connect at least 1f ceramic output capacitor. 3 en2 enable input for ldo2. acti ve high input. logic high = on; logi c low = off; do not leave floating. 4 dc enable input for led driver. can be used for dimming using the digital control interface. see digital dimming interface for details. do not leave floating. 5 rset an internal 1.27v reference sets the nominal maximum led current. example, apply a 20.5k ? resistor between rset and gnd to set led current to 20ma at 100% duty cycle. 6 d1 led1 driver. connect led anode to vin and cathode to this pin. 7 d2 led2 driver. connect led anode to vin and cathode to this pin. 8 d3 led3 driver. connect led anode to vin and cathode to this pin. 9 gnd ground. 10 d4 led4 driver. connect led anode to vin and cathode to this pin. 11 d5 led5 driver. connect led anode to vin and cathode to this pin. 12 d6 led6 driver. connect led anode to vin and cathode to this pin. 13 en1 enable input for ldo1. ac tive high input. logic high = on; logi c low = off; do not leave floating. 14 ldo1 output of ldo1. connect at least 1f ceramic output capacitor. epad hs pad heat sink pad. not intern ally connected. connect to ground. downloaded from: http:///
micrel inc. mic2846a april 2010 4 m9999-041210-d absolute maximum ratings (1) main input voltage (v in ) ................................... -0.3v to +6v enable input voltage (v dc , v en1 , v en2 ) ............ -0.3v to +6v led driver voltage (v d1-d6 ).............................. -0.3v to +6v power dissipation ................................. in ternally limited (3) lead temperature (solde ring, 10sec .)....................... 260c storage temperature (t s ) ..........................-65c to +150c esd rating (4) ................................................. esd sensitive operating ratings (2) supply voltage (v in ).................................. +3.0v to +5.5v enable input voltage (v dc , v en1 , v en2 ) .............. 0v to v in led driver voltage (v d1-6 ) ................................. 0v to v in junction temperature (t j ) .....................C40c to +125c junction thermal resistance 2.5mm x 2.5mm thin mlf-14l ( ja ) ..............89c/w electrical characteristics linear wled drivers v in = v dc = 3.8v, v en1 = v en2 = 0v, r set = 20.5k ? ; v d1-d6 = 0.6v; t j = 25 c, bold values indicate C40 c t j 125 c; unless noted. parameter conditions min typ max units current accuracy (5) 1.5 % matching (6) 1.5 % drop-out where i led = 90% of led current seen at v dropnom = 0.6v, 100% brightness level 40 80 mv ground/supply bias current i led = 20ma 1.4 1.8 ma shutdown current (current source leakage) v dc = 0v for more than 1260s 0.01 1 a digital dimming logic low 0.2 v v dc input voltage (v dc ) logic high 1.2 v v dc enable input current v dc = 1.2v 0.01 1 a t shutdown time dc pin is low to shutdown the device 1260 s t mode_up time dc pin is low to change to count up mode 100 160 s t mode_down time dc pin is low to change to count down mode 420 500 s t prog_high , t prog_low time for valid edge count; ignored if outside limit range 2 32 s t delay time dc pin must remain high before a mode change can occur 100 s t prog_setup first down edge must occur in this window during presetting brightness 5 75 s t start_up delay time starting when dc is first pulled high until leds start up 140 s ldos v in = v en1 = v en2 = 3.8v, v dc = 0v; c out1 = c out2 = 1 f, i out1 = i out1 = 100 a; t j = 25c, bold values indicate C40 c t j 125 c; unless noted. parameter conditions min typ max units output voltage accuracy variation from nominal v out -2 -3 +2 +3 % % v in line regulation 0.02 0.3 %/v load regulation i out = 100 a to 150ma 7 mv dropout voltage (7) v out >= 3.0v; i out = 150ma 150 330 mv ground pin current 35 70 a ground pin current in shutdown v en = 0v 0.05 1.0 a downloaded from: http:///
micrel inc. mic2846a april 2010 5 m9999-041210-d ldos (continued) parameter conditions min typ max units ripple rejection f = 1khz; c out = 2.2 f 65 db current limit v out = 0v 175 300 500 ma output voltage noise frequency 10hz to 100khz 200 v rms enable inputs (en1,2) logic low 0.2 v enable input voltage logic high 1.2 v enable input current v en1 = v en1 = 1.2v 0.01 1 a turn-on time c out = 1f; 90% of v out 50 100 s notes: 1. exceeding the absolute maxi mum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. the maximum allowable power dissipation of any t a (ambient temperature) is p d(max) = (t j(max) C t a ) / ja . exceeding the maximum allowable power dissipation will result in excessive die temperatur e, and the regulator will go into thermal shutdown (150c). 4. devices are esd sensitive. handling precaut ions recommended. human body model (hbm), 1.5k ? in series with 100pf. 5. as determined by average current of all channels in use and all channels loaded. 6. the current through each channel meets the stated limits from the average current of all channels. 7. dropout voltage is defined as the input-output differential at which the output voltage drops 2% below its nominal value me asured at v in = v out + 1v. downloaded from: http:///
micrel inc. mic2846a april 2010 6 m9999-041210-d typical characteristics (wled driver) downloaded from: http:///
micrel inc. mic2846a april 2010 7 m9999-041210-d typical characteristics (ldo) downloaded from: http:///
micrel inc. mic2846a april 2010 8 m9999-041210-d functional characteristics (wled driver) downloaded from: http:///
micrel inc. mic2846a april 2010 9 m9999-041210-d functional characteristics (ldo) downloaded from: http:///
micrel inc. mic2846a april 2010 10 m9999-041210-d functional diagram figure 1. mic2846a functional block diagram functional description the mic2846a is a six channel linear led driver with dual 150ma ldos. the led driver incorporates a dynamic averaged matching tm (dam tm ) technique designed specifically to opt imize on current accuracy and matching across process variation. it can maintain proper current regulation with led current accuracy of 1.5% while the typical matching between the six channels is 1.5% at room temperature. the led currents are independently driv en from the input supply and will maintain regulation with a dropout of 40mv at 20ma. the low dropout of t he linear led drivers allows the leds to be driven direct ly from the battery voltage and eliminates the need for boost or large and inefficient charge pumps. the maximum led current for each channel is set via an external resistor while a single-wire digital interface controls dimming. the mic2846a has two ldos with a dropout voltage of 150mv at 150ma and consume 35a of current in operation. each ldo has an independent enable pin, which reduces the operating current to less than 1a in shutdown. both linear regulators are stable with just 1f of output capacitance. block diagram as shown in figure 1, the mic2846a consists of two ldos with six current mirrors set to copy a master current determined by r set . the linear led drivers have a designated control block for enabling and dimming of the leds. the mic2846a dimming is controlled by the digital control block that receives digital signals for dimming. the ldos each have their own control and are independent of the linear led drivers. each ldo consists of internal feedback resistors, an error amplifier, a pfet transistor and a control circuit for enabling. downloaded from: http:///
micrel inc. mic2846a april 2010 11 m9999-041210-d vin the input supply (vin) provi des power to the ldos, the linear led drivers and the control circuitry. the v in operating range is 3v to 5.5v. a minimum bypass capacitor of 1f should be placed close to the input (vin) pin and the ground (gnd) pin. refer to the layout recommendations section for details on placing the input capacitor (c1). ldo1/ldo2 the output pins for ldo one and ldo two are labeled ldo1 and ldo2, respectively. a minimum of 1f bypass capacitor should be placed as close as possible to the output pin of each ld o. refer to the layout recommendations section for details on placing the output capacitor (c2, c3) of the ldos. en1/en2 a logic high signal on the enable pin activates the ldo output voltage of the device. a logic low signal on the enable pin deactivates the output and reduces supply current to less than 1a. en1 controls ldo1 and en2 controls ldo2. do not leave these control pins floating. dc the dc pin is used to enable and control dimming of the linear drivers on the mic2846a. see the mic2846a digital dimming interface in the application information section for details. pulling the dc pin low for more than 1260 s puts the mic2846a into a low i q sleep mode. the dc pin cannot be left floating; a floating enable pin may cause an indeterminate state on the outputs. a 200k ? pull down resistor is recommended. r set the r set pin is used by connecting a r set resistor to ground to set the peak current of the linear led driver. the average led current can be calculated by the equation (1). i led (ma) = 410 * adc / r set (k ? ) (1) adc is the average duty cy cle of the led current controlled by the single-wire digital dimming. see table 1 for adc values. when the device is fully on the average duty cycle equals 100% (adc=1). a plot of i led versus r set at 100% duty cycle is shown in figure 2. figure 2. peak led current vs. r set (100% duty cycle) d1-d6 the d1 through d6 pins are the led driver for led 1 through 6, respectively. the anodes of the leds are connected to vin and the cathodes of the leds are connected to d1 through d6. when operating with less than six leds, leave the unused d pins unconnected. the six led channels are independent of one another and may be combined or used separately. during start- up, the d1 through d6 channels are turned on in synchronization at around 250s apart. gnd the ground pin is the ground path for the linear drivers and ldos. the ground of the input capacitor should be routed with low impedance traces to the gnd pin and made as short as possible. refer to the layout recommendations for more details. downloaded from: http:///
micrel inc. mic2846a april 2010 12 m9999-041210-d application information brightness level (0 - 48) average duty cycle (%) average i led (ma) i peak (ma) 0 100 12 1 80 9.6 2 60 7.2 3 48.33 5.8 4 36.67 4.4 5 29.17 3.5 6 21.67 2.6 7 16.67 2 8 11.67 1.4 9 9.17 1.1 10 6.67 0.8 11 5 0.6 12 3.33 0.4 13 2.5 0.3 14 1.67 0.2 15 0.83 0.1 60% of i peak r set = 20.5k ? i peak = 12ma 16 0 0 0 17 0.83 0.1 60% of i peak 18 0.83 0.17 19 1.25 0.25 20 1.67 0.33 21 2.08 0.42 22 2.5 0.5 23 2.92 0.58 24 3.33 0.67 25 4.17 0.83 26 5 1 27 5.83 1.17 28 6.67 1.33 29 7.92 1.58 30 9.17 1.83 31 10.42 2.08 32 11.67 2.33 33 14.17 2.83 34 16.67 3.33 35 19.17 3.83 36 21.67 4.33 37 25.42 5.08 38 29.17 5.83 39 32.92 6.58 40 36.67 7.33 41 42.5 8.5 42 48.33 9.67 43 54.17 10.83 44 60 12 45 70 14 46 80 16 47 90 18 48 100 20 100% of i peak r set = 20.5k ? i peak = 20ma table 1. digital interface brightness level table dynamic average matching (dam?) the dynamic average matching? architecture multiplexes four voltage references to provide highly accurate led current and channel matching. the mic2846a achieves industry leading led channel matching of 1.5% across the entire dimming range. high current parallel operation 6 digital figure 3. high current led driver circuit the linear drivers are independent of each other and can be used individually or paralleled in any combination for higher current 4applications. a single wled can be driven with all 6 linear drivers by connecting d1 through d6 in parallel to the cathode of the wled as shown in figure 3. this will generate a current 6 times the individual channel current and can be used for higher current wleds such as those used in flash or torch applications. digital dimming the mic2846a utilizes an in ternal dynamic pulse width to generate an average duty cycle for each brightness level. by varying the duty cycle the average current achieves 49 logarithmically spaced brightness levels. this generates a brightness scale similar to the perception of brightness seen by the human eye. figure 4 shows the led current at different brightness levels. when dimming, the d1 through d6 pins are 60 out of phase from each other to reduce electromagnetic interference. the mic2846a uses an internal frequency of approximately 700hz to dim the wleds. with the period of approximately 1.43ms, the 60 phase shift equates to a timing offset of 238 s. as shown in figure 5, brightness level 32 was selected to show the phase shift across the channels. downloaded from: http:///
micrel inc. mic2846a april 2010 13 m9999-041210-d figure 4. led current with brightness level change figure 5. led current 60 phase shift digital dimming interface the mic2846a incorporates an easy to use single-wire, serial programming interface that allows users to set led brightness up to 49 different levels, as shown in the table1. brightness levels 0 through 15 are logarithmically spaced with a peak current equal to 60% of the current programmed by r set . brightness level 16 is provided for applications that want to fade to black with no current flowing through the leds. brightness level 17 has the same duty cycle as level 18, but the peak current is only 60% of the current set by r set ; therefore, the average current is 0.1ma. brightness levels 18 through 48 are also logarithmically spaced, but the peak current is equal to 100% of the current determined by r set . refer to table 1 for the translation from brightness level to average led duty cycle and current. the mic2846a is designed to receive programming pulses to increase or decrease brightness. once t he brightness change signal is received, the dc pin is simply pulled high to maintain the brightness. this set and forget feature relieves processor computing power by eliminating the need to constantly send a pwm signal to the dimming pin. with a digital control interface, brightness levels can also be preset so that leds can be turned on at any particular brightness level. start up assuming the mic2846a has been off for a long time and no presetting brightness command is issued (presetting is discussed in a later section), the mic2846a will start-up in its default mode approximately 140s (t start_up ) after a logic level high is applied to the dc pin, shown in figure 6. in the default mode the leds are turned on at the maximum brightness level of 48. each falling edge during the t prog_setup period will cause the default brightness level to decrease by one. this is discussed in more detail in the presetting brightness section. figure 6. typical start-up timing shutdown whenever the dc input pin is pulled low for a period greater than or equal to t shutdown (1260s), the mic2846a will be shutdown as shown in figure 7. figure 7. shutdown timing once the device is shutdown, the control circuit supply is disabled and the leds are turned off, drawing only 0.01a. brightness level information stored in the mic2846a prior to sh utdown will be erased. count up mode/count down mode the mode of mic2846a can be in either count up mode or count down mode. the count down/up modes determine what the falling edges of the programming pulses will do to the brightness. in count up mode, subsequent falling ed ges will increase brightness while in count down mode, subsequent falling edges will decrease brightness. by def ault, the mic2846a is in count down mode when first turned on. 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), shown in figure 8. the device will remain in downloaded from: http:///
micrel inc. mic2846a april 2010 14 m9999-041210-d count up mode until its mode is changed to count down mode or by disabling the mic2846a to reset the mode back to default. figure 8. mode change to count up to change the mode back to count down mode, pull the dc pin low for a period equal to t mode_down (420s to 500s), shown in figure 9. now the internal circuitry will remain in count down mode until changed to count up as described previously. figure 9. mode change to count down programming the brightness level mic2846a is designed to start driving the leds 140s (t start_up ) after the dc pin is first pulled high at the maximum brightness level of 48. after start up, the internal control logic is ready to decrease the led brightness upon receiving programming pulses (negative edges applied to dc pin). since mic2846a starts in count down mode, the brightness level can be decreased without a mode change by applying two programming pulses, as shown in figure10. note that the extra pulse is needed to decrease brightness because the first edge is ig nored. anytime the first falling edge occurs later than 32s after a mode change, it will be ignored. ignoring the first falling edge is necessary in order that mode change (t mode_up , t mode_down ) pulses do not result in adjustments to the brightness level. each programming pulse has a high (t prog_high ) and a low (t prog_low ) pulse width that must be between 2s to 32s. the mic2846a will reme mber the brightness level and mode it was changed to. for proper operation, ensure that the dc pin remains high for at least t delay (140s) before issuing a mode change command. figure10. brightness programming pulses multiple brightness levels can be set as shown in figure 11. when issuing multiple brightness level adjustments to the dc pin, ensure both t prog_low and t prog_high are within 2s to 32s. to maintain operation at the current brightness level simply maintain a logic level high at the dc pin. figure11. decreasing brightness several levels as mentioned, mic2846a can be programmed to set led drive current to produce one of 49 distinct brightness levels. the internal logic keeps track of the brightness level with an up/down counter circuit. the following section explains how the brightness counter functions with continued programming edges. counter roll-over the mic2846a internal up/down counter contains registers from 0 to 48 (49 levels). when the brightness level is at 0 and a programming pulse forces the brightness to step down, then the counter will roll-over to level 48. this is illustrated in figure 12. figure 12. down counter roll-over downloaded from: http:///
micrel inc. mic2846a april 2010 15 m9999-041210-d similarly, when the counter mode is set to count up and a programming pulse forces the brightness level to step up from level 48, then the counter will roll-over to level 0 as illustrated in figure 13. figure 13. up counter roll-over one-step brightness changes the one-step brightness change procedure relieves the user from keeping track of the mic2846as up/down counter mode. it combines a mode change with a programming edge; therefore, regardless of the previous count mode, it will change the brightness level by one. figure 14. one-step brightness decrease the one-step brightness decrease method is quite simple. first, the dc pin is pulled low for a period equal to the t mode_down (420s to 500s) and immediately followed by a falling edge within t prog_high (2s to 32s) as shown in figure 14. this will decrease the brightness level by 1. similarly a one-step brightness 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 (2s to 32s). figure 15 illustrates the proper timing for execution of a one-step brightness increase. figure 15. one-step brightness increase presetting brightness presetting the brightness will allow the mic2846a to start-up at any brightness level (0 to 48). the mic2846a does not turn on the linear led driver until the dc pin is kept high for t start_up (140s). this grants the user time to preset the brightness level by sending a series of programming edges via the dc pin. the precise timing for the first down edge is between 5s to 75s after the dc pin is first pulled high. the 70s timeframe between 5s and 75s is the t prog_setup period. the first presetting pulse edge must occur somewhere between the timeframe of 5s to 75s, otherwise the mic2846a may continue to start up at the full (default) brightness level. figure 16. presetting timing figure 16 shows the correct presetting sequence to set the mic2846a brightness to level 39 prior to start up. notice that when using the presetting feature the first programming pulse is not ignored. this is because the counters default mode is count down and a mode change cannot be performed in the presetting mode. (note that the t prog_high and t prog_low pulse width must still be between 2s to 32s.) downloaded from: http:///
micrel inc. mic2846a april 2010 16 m9999-041210-d ldo mic2846a ldos are low noise 150ma ldos. the mic2846a ldo regulator is fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. input capacitor the mic2846a stability can be maintained using a ceramic input capacitor of 1f. low-esr ceramic capacitors provide optimal performance at a minimum amount of space. additional high-frequency capacitors, such as small-valued npo dielectric-type capacitors, help filter out high-frequency noise and are good practice in any noise sensitive circuit. x5r or x7r dielectrics are recommended for the input capacitor. y5v dielectrics lose most of their capacitance over temperature and are theref ore, not recommended. output capacitor the mic2846a ldos require an output capacitor of at least 1f or greater to maintain stability, however, the output capacitor can be increased to 2.2f to reduce output noise without increasing package size. the design is optimized for use with low-esr ceramic chip capacitors. high esr capacitors are not recommended because they may cause hi gh frequency oscillation. x7r/x5r dielectric-type ceramic capacitors are recommended due to their improved temperature performance compared to z5u and y5v capacitors. x7r-type capacitors change c apacitance by 15% over their operating temperature range and are the most stable type of ceramic capacitors. z5u and y5v dielectric capacitors change value by as much as 50% and 60%, respectively, over t heir operating temperature ranges. to use a ceramic chip capacitor with y5v dielectric, the value must be much higher than an x7r ceramic capacitor to ensure the same minimum capacitance over the equivalent operating temperature range. no-load stability unlike many other voltage regulators, the mic2846a ldos will remain stable and in regulation with no load. thermal considerations the mic2846a ldos are each designed to provide 150ma of continuous current. maximum ambient operating temperature can be calculated based on the output current and the voltage drop across the part. for example if the input voltage is 3.6v, the output voltage is 2.8v, and the output current = 150ma. the actual power dissipation of the regulator circuit can be determined using the equation: p ldo1 = (v in C v out1 ) i out + v in i gnd because this device is cmos and the ground current (i gnd ) is typically <100a over the load range, the power dissipation contributed by t he ground current is < 1% and can be ignored for this calculation. p ldo1 = (3.6v C 2.8v) 150ma p ldo1 = 0.120w since there are two ldos in the same package, the power dissipation must be calculated individually and then summed together to arrive at the total power dissipation. p total = p ldo1 + p ldo2 to determine the maximum ambient operating temperature of the package, use the junction-to-ambient thermal resistance ( ja = 60c/w) of the device and the following basic equation: ? ?? ? ? ?? ? ? = ja a j(max) total(max) t t p t j(max) = 125c, is the maximum junction temperature of the die and ja, is the thermal resistance = 60c/w. substituting p total for p total(max) and solving for the ambient operating temperature will give the maximum operating conditions for the regulator circuit. for example, when operating the mic2846a ldos (ldo1=2.8v and ldo2=1.5v) at an input voltage of 3.6v with 150ma load on each, the maximum ambient operating temperature t a can be determined as follows: p ldo1 = (3.6v C 2.8v) 150ma = 0.120w p ldo2 = (3.6v C 1.5v) 150ma = 0.315w p total =0.120w+ 0.315w = 0.435w = (125c C t a )/(60c/w) t a = 125c C 0.435w 60c/w t a = 98.9c therefore, under the abov e conditions, the maximum ambient operating temperature of 98.9c is allowed. downloaded from: http:///
micrel inc. mic2846a april 2010 17 m9999-041210-d mic2846a typical application circuit 6 digital bill of materials item part number manufacturer description qty. c1608x5r0j105k tdk (1) 06036d105kat2a avx (2) grm188r60j105ke19d murata (3) c1, c2, c3 vj0603g225kxyat vishay (4) ceramic capacitor, 1f, 6.3v, x5r, size 0603 1 swts1007 seoul semiconductor (5) d1 C d6 99-116unc everlight (6) wled 6 r1 crcw060320k5f5ea vishay (4) resistor, 20.5k, 1%, 1/16w, size 0603 1 r2 crcw06032003fkea vishay (4) resistor, 200k, 1%, 1/16w, size 0603 1 u1 mic2846a-xxymt micrel, inc. (7) 6 channel digital control linear wled driver with dam? and dual low iq ldo 1 notes: 1. tdk: www.tdk.com 2. avx: www.avx.com 3. murata: www.murata.com 4. vishay: www.vishay.com 5. seoul semiconductor: www.seoulsemicon.com 6. everlight: www.everlight.com 7. micrel, inc.: www.micrel.com downloaded from: http:///
micrel inc. mic2846a april 2010 18 m9999-041210-d pcb layout recommendations (fixed) top layer bottom layer downloaded from: http:///
micrel inc. mic2846a april 2010 19 m9999-041210-d package information 14-pin (2.5mm x 2.5mm) thin mlf ? (mt) 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 authori zed for use as components in life support app liances, devices or systems where malfu nction of a product can reasonably be expected to result in pers onal injury. life support devices or system s are devices or systems that (a) are in tended 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 significant injury to the user. a purchasers use or sale of micrel produc ts for use in life support app liances, devices or systems is a purchasers own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2009 micrel, incorporated. downloaded from: http:///

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