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mic2845/6 6 channel high side current source wled driver with dual low i q ldos 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 january 2008 m9999-010808-a general description the mic2845 and mic2846 are all-in-one integrated circuits designed for driving white leds (wleds) for display backlighting, camera flash, and other modules in mobile devices. the mic2845/6 uses 6 channels of current sinks to maintain constant cu rrent for up to 6 wleds. it features a typical dropout of less than 50mv at 20ma and guarantees less than 100mv over all conditions, thus allowing the wleds to be driven directly from the battery without the use of extra capacitors in a large and costly charge pump. the current sinks are accurate up to 95% while the matching between each channel is guaranteed above 96.5% at room temperat ure. the superior matching of mic2845/6 insures clear and uniform display brightness under all conditions. the brightness of wleds is be externally preset by a resistor or internally programmed using pulse width modulation (pwm) on the mic2845 or single-wire digital control on the mic2846. the pwm brightness control on the mic2845 will operate down to less than 1% duty cycle for an accurate and a high dynamic brightness range. the mic2846 dimming features a single-wire digital interface which takes commands from digital programming pulses to change the brightness in a logarithmic scale similar to the eye?s perception of brightness. the single-wire digital brightness control is divided into two modes of operation for full brightness mode or battery saving mode for a total of 32 total brightness steps. the mic2845/6 also featur es two independently enabled low quiescent current ldos . each ldo offers 3% accuracy from the nominal voltage over temperature, low dropout voltage (150mv @ 150ma), and low ground current at all load conditions (typically 25a). both ldos can be turned off to draw virtually no current. the mic2845/6 are both 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. datasheets and support documentation can be found on micrel?s web site at: www.micrel.com. features ? input voltage range: 3.0v to 5.5v wled driver ? current source dropout of less than 50mv guaranteed at 20ma ? accuracy better than 95% (-40 c to +125 c) ? mismatching lower than 3.5% (20c) ? maintains proper regulation regardless of how many channels are utilized ? flash led driver paralleling 6 channels ? two methods of dimming control ? mic2845 ? pwm operation to <1% duty cycle ? mic2846 ? single wire digital control ldos ? very low ground current ? <25a each @ 150ma ? stable with 1f ceramic output capacitor ? dropout at 150mv at 150ma ? thermal shutdown and current limit protection applications ? mobile handsets ? digital cameras ? portable media/mp3 players ? portable navigation devices (gps) ? portable applications
micrel inc. mic2845/46 january 2008 2 m9999-010808-a typical application ordering information part number ldo1 output voltage ldo2 output voltage mark code temperature range package mic2845-mfymt 2.8v 1.5v ynmf ?40c to +125c 14-pin 2.5x2.5 mlf ? MIC2845-MGYMT 2.8v 1.8v ynmg ?40c to +125c 14-pin 2.5x2.5 mlf ? mic2846-mfymt 2.8v 1.5v ypmf ?40 c to +125c 14-pin 2.5x2.5 mlf ? mic2846-mgymt 2.8v 1.8v ypmg ?40 c to +125c 14-pin 2.5x2.5 mlf ? note: 1. output voltage range of each ldo is 1.0v to 3.3v in 50mv steps. contact micrel marketing for other voltage options. pin configuration mic2845 mic2846 2.5mm x 2.5mm thin mlf ? (top view) 2.5mm x 2.5mm thin mlf ? (top view)
micrel inc. mic2845/46 january 2008 3 m9999-010808-a pin description pin number mic2845 pin number mic2846 pin name pin function 1 1 vin voltage input. connect at le ast 1f ceramic capacitor between v in and gnd. 2 2 ldo2 output of ldo2. connect at least 1f ceramic output capacitor. 3 3 en2 enable input for ldo2. active high input. logic high = on; logic low = off; do not leave floating. 4 - end enable high side current source. this pin can be used as a pwm input for dimming of wleds. do not leave floating. - 4 dc digital control input for high side current source. see digital dimming interface. do not leave floating. 5 5 r set an internal 1.27v reference sets the nominal maximum wled current. example, apply a 20.5k ? resistor between r set and gnd to set led current to 20ma at 100% duty cycle. 6 6 d1 led1 current sink input. connect led anode to vin and cathode to this pin. 7 7 d2 led2 current sink input. connect led anode to vin and cathode to this pin. 8 8 d3 led3 current sink input. connect led anode to vin and cathode to this pin. 9 9 gnd ground. 10 10 d4 led4 current sink input. connect led anode to vin and cathode to this pin. 11 11 d5 led5 current sink input. connect led anode to vin and cathode to this pin. 12 12 d6 led6 current sink input. connect led anode to vin and cathode to this pin. 13 13 en1 enable input for ldo1. active high input. logic high = on; logic low = off; do not leave floating. 14 14 ldo1 output of ldo1. connect a 1f ceramic output capacitor.
micrel inc. mic2845/46 january 2008 4 m9999-010808-a absolute maximum ratings (1) main input voltage (v in ) ................................... -0.3v to +6v enable/dc input volt age ................................. -0.3v to +6v current source voltage ????????? ...-0.3v to +6v power dissipation????????? ..internally limited (3) lead temperature (solde ring, 10sec .)....................... 260c storage temperature (t s ) ..........................-65c to +150c esd rating (4) .................................................................. 2kv operating ratings (2) supply voltage (v in )..................................... +3.0v to +5.5v enable input voltage (v en1/2 ,v dc ,v end ) ................. 0v to v in current source voltage (v d1-6 ) .............................. 0v to v in junction temperature (t j ) ........................ ?40c to +125c junction thermal resistance mlf ? ( ja )..........................................................60c/w electrical characteristics linear regulators v in = v en1 = v en2 = 3.8v, v dc (2846) v end (2845) = 0v; c out1/2 = 2.2f, i out1/2 = 100a; t j = 25 c, bold values indicate ?40 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 6 10 mv dropout voltage v out > = 3.0v; i out = 150ma 150 330 mv ground pin current i out = 100 a to 150ma 25 40 a ground pin current in shutdown v en < 0.2v, t j < 85c 0.05 1.0 a ripple rejection f = up to 1khz; c out = 2.2 f 65 db current limit v out = 0v 200 300 550 ma output voltage noise c out = 2.2 f, 10hz to 100khz 58 v rms enable inputs (en1, 2) logic low 0.2 v enable input voltage logic high 1.2 v enable hysterisis 25 mv enable input current v en1/2 > 1.0v 0.01 1 a turn-on time c out = 2.2f; 90% of v out 50 100 s notes: 1. exceeding the absolute maximum 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) ? t a ) / ja . exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 4. devices are esd sensitive. handling pr ecautions recommended. human body model: 1.5k ? in series with 100pf.
micrel inc. mic2845/46 january 2008 5 m9999-010808-a wled current sinks v in = v dc (2846) v end (2845) = 3.8v, v en1 = v en2 = 0v; r set = 20.5k ? ; v drop = 0.6v; t j = 25 c, bold values indicate ?40 c t j 125 c; unless noted. parameter conditions min typ max units current accuracy (5) v dropnom = 0.6v -5 +5 % matching (6) v dropnom = 0.6v -3.6 -5.5 +3.6 +5.5 % % drop-out where i led = 90% of led current seen at v dropnom = 0.6v, 100% brightness level 50 100 mv ground/supply bias current i out = 20ma 1.0 ma shutdown current (current source leakage) v end = 0v or v dc = 0v > 1260s, v enldo1,2 = 0v 0.01 1 a mic2845- pwm dimming logic low 0.2 v enable input voltage v end logic high 1.2 v enable input current v ih > 1.0v 0.01 1 a minimum pulse width 10 s current source delay (50% levels) shutdown to on (5) standby to on; v drop = 0.1v standby to on; v drop = 0.6v on to standby; v drop = 0.1v on to standby; v drop = 0.6v r set = 20.5k 125 1 0.5 1 1 s s s s s current source transient time (10%-90%) t rise , v drop = 0.1v t rise , v drop = 0.6v t fall ; v drop = 0.1v t fall , v drop = 0.6v 1 1 0.3 0.3 s s s s stand-by to shutdown time v end = 0v 20 tbd 40 ms mic2846- digital dimming logic low 0.2 v v dc input voltage v dc logic high 1.2 v vdc enable input current v ih > 1.2v 0.01 1 a t shutdown time dc pin is low to put into shutdown 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 1 32 s t delay time dc pin must remain high before a mode change can occur 140 s t prog_setup first down edge must occur in this window during presetting brightness 35 50 s t start_up delay from dc is high to start up 140 s notes: 5. as determined by average current of all channels in use and all channels loaded. 6. the current through each led meet the stated limits from the average current of all leds. 7. maximum differential in forward voltage anticipated from the led with the highest forward voltage to the led with the lowest forward voltage at nominal current. 8. current accuracy guaranteed for v drop current source 100mv to v in -1.2v. 9. dropout voltage is defined as the input-output differential at which the output voltage drops 2% below its nominal value mea sured at 1v differential.
micrel inc. mic2845/46 january 2008 6 m9999-010808-a typical characteristics (current sink)
micrel inc. mic2845/46 january 2008 7 m9999-010808-a typical characteristics (ldo)
micrel inc. mic2845/46 january 2008 8 m9999-010808-a functional characteristics (current sink)
micrel inc. mic2845/46 january 2008 9 m9999-010808-a functional characteristics (current sink)
micrel inc. mic2845/46 january 2008 10 m9999-010808-a functional characteristics (current sink)
micrel inc. mic2845/46 january 2008 11 m9999-010808-a functional diagram figure 1. mic2845 and mic2846 functional block diagram functional description the mic2845/6 is a 6 channels wled driver with dual 150ma ldos. the wled driver is designed to maintain proper current regulation with led current accuracy of 95% while the minimum matching between the 6 channels to be 96.5% at room temperature. the wleds are driven independently from the input supply and will maintain regulation with a dropout of 50mv at 20ma. the low dropout of the current sinks allows the wleds to be driven directly from the input voltage and eliminates the need for large and inefficient charge pumps. if desired, multiple channels can be combined to drive a single wled at a higher current for an intense light output. the combined method generates an extremely bright light suited for camera flash applications. the maximum wled current for each channel is set via an external resistor. if dimming is desired the mic2845 can dim via a pwm signal while the mic2846 is controlled by a single-wire digital interface. both dimming controls will be discussed in detail in the following sections. the mic2845/6 has two ldos with a dropout voltage of 150mv at 150ma and consume 25a of current in operation. each ldo has a dedicated enable pin, which can reduce operating current down to 0.01a in shutdown. both linear regulators are stable with just 1f of output capacitance. block diagram as shown in figure 1, the mic2845/6 consists of 2 ldos and 6 current mirrors set to copy a master current determined by r set . the current sinks have a designated control block for enabling and dimming of the wleds. the mic2845 is controlled by the pwm control block that receives pwm signals for dimming. the mic2846 dimming is controlled by an internal digital control interface. the ldos each have their own control block and are independent of the current sinks. in each ldo block, there are internal feedback resistors, an error amplifier, a pfet transistor and a control circuit for enabling.
micrel inc. mic2845/46 january 2008 12 m9999-010808-a v in the input supply (v in ) provides power to the ldos, the current sinks and the control circuitry. the v in operating range is 3v to 5.5v. due to wire inductance a minimum of 1f/6.3v bypass capacitor should be placed close to 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 0.01a. en1 controls ldo1 and en2 controls ldo2. mic2845/6 ldos feature built-in soft-start circuitry that reduces in-rush current and prevents the output voltage from overshooting at start up. do not leave floating. end (mic2845 only) the end pin is equivalent to the enable pin for the current sinks on the mic2845. it can also be used for dimming using a pwm signal. see the mic2845 pwm dimming interface in the app lication information section for details. dc (mic2846 only) the dc pin is equivalent to the enable pin for the current sinks on the mic2846. it can also be used for dimming using a single-wire digital interface. see the mic2846 digital dimming interface in the application information section for details. r set the r set pin is used by connecting a r set resistor to ground to set the peak current of the current sinks. the average led current can be calculated by the equation (1) below: i led (ma) = 410 * d / r set (k ? ) (1) d is the duty cycle of the led current during pwm dimming (mic2845) or single-wire digital dimming (mic2846). when the device is fully on the duty cycle equals 100% (d = 1). a plot of i led versus r set at 100% duty cycle is shown in figure 2. figure 2. peak i led vs. r set d1-d6 the d1 through d6 pins are the current sink inputs for wled 1 through 6, respectively. connect the anodes of the wleds to v in and each cathode of the wleds to d1 through d6. the current sinks are independent of each other. they can be used individually or combined. a single wled can be driven with all 6 current sinks by connecting d1 through d6 together with the cathode of the wled. this will generate a current 6 times i led and can be used for higher current wleds such as those used in flash applications. the peak current of each current sink is 80ma at 10 0% duty cycle due to thermal limitations. with all 6 current sinks, the total current to drive a single flash wled is 480ma. if the duty cycle is lowered to 10% of 1 second, a wled can be driven over 1.5a by sinking 250ma on each channel, shown in figure 3. figure 3. flash led driver circuit gnd the ground pin is the ground path for the current sinks as well as the ldos. the current loop for the ground should be as small as possible. the ground of the input and output capacitors 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.
micrel inc. mic2845/46 january 2008 13 m9999-010808-a application information mic2845 pwm dimming interface the mic2845 can receive pwm signals from the end pin for wled dimming. the frequency of the pwm signal should be between 200hz ? 1khz and the duty cycle can range from 1% to 100%. dimming is generated by pulsing the wleds on and off in synchronization with the pwm signal. an internal shutdown delay ensures that the internal control circuitry remains active during pwm dimming for optimum performance. figure 4 through figure 8 show the wled current response when a pwm signal is applied to the end pin. figure 4. pwm signal at 1% duty cycle figure 5. pwm signal at 20% duty cycle figure 6. pwm signal at 50% duty cycle figure 7. pwm signal at 80% duty cycle figure 8. pwm signal at 100% duty cycle
micrel inc. mic2845/46 january 2008 14 m9999-010808-a mic2846 digital dimming interface the mic2846 incorporates an easy to use single-wire, serial programming interface that allows users to set wled brightness up to 32 different levels, as shown in table 1. level (0-31) led duty cycle (%) average i led (ma) i peak (ma) 0 100 12 1 86 10.32 2 72 8.6 3 59 7.1 4 45.5 5.5 5 36.5 4.4 6 29.5 3.5 7 22.5 2.7 8 18 2.2 9 13.5 1.6 10 9.5 1.1 11 8 0.96 12 6 0.72 13 5 0.6 14 4 0.48 15 1.6 0.192 60% of i ledpeak (12ma for r set = 20.5k) 16 1.6 0.32 17 4 0.8 18 5 1 19 6 1.2 20 8 1.6 21 9.5 1.9 22 13.5 2.7 23 18 3.6 24 22.5 4.5 25 29.5 5.9 26 36.5 7.3 27 45.5 9.1 28 59 11.8 29 72 14.4 30 86 17.2 31 100 20 100% of i ledpeak (20ma for r set = 20.5k) table 1. digital interface brightness level table brightness levels 0-15 is logarithmically spaced with a peak current equal to 60% of the current set by r set. brightness levels 16-31 is also logarithmically spaced with a peak current equal to the current determined by r set. spacing between each leve l is in logarithmic scale by design to mimic the sens itivity of the human eye. refer to table 1 for the translation from brightness level to led duty cycle and current. the mic2846 is designed to receive programming pulses to increase or decrease brightness. once the 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 wleds can be turned on at any particular brightness level. start up assuming the mic2846 has been off for a long time and no presetting brightness command is issued (presetting is discussed in a later sect ion), the mic2846 will start-up in its default mode approximately 140s (t start_up ) after a logic level high is applied to the dc pin. in the default mode the wleds are turned on at the maximum brightness level of 31. each falling edges during the t prog_setup period will cause the de fault brightness level to decrease by one. this is discussed in more detail in the presetting brightness section. figure 9. 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 mic2846 will be in shutdown, shown in figure 10. figure 10. shutdown timing once the device is shutdown, the control circuit supply is disabled and the wleds are turned off, drawing only 0.01a. brightness level information stored in the mic2846 prior to shutdown will be erased. count up mode/count down mode the mode of mic2846 can be in either count up mode or count down mode. the counting modes determine what the falling edges of the programming pulses will do
micrel inc. mic2845/46 january 2008 15 m9999-010808-a to the brightness. in count up mode, subsequent falling edges will increase brightness while in count down mode, subsequent falling edges will decrease brightness. by default, the mic2846 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 11. the device will rema in in count up mode until its mode is changed to count down mode or by disabling the mic2846 to reset the mode back to default. figure 11. 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 12. now the internal circuitry will remain in count down mode until changed to count up as described previously. figure 12. mode change to count down programming the brightness level mic2846 is designed to start driving the wleds 140s (t start_up ) after the dc pin is first pulled high at the maximum brightness level of 31. after start up, the internal control logic is ready to decrease the wled brightness upon receiving programming pulses (negative edges applied to dc pin). since mic2846 starts in count down mode, the brightness level is decreased one level by applying two programming pulses, as shown in figure 13. note that the extra pulse is needed to decrease brightness because the first edge is ignored. anytime the first falling edge happens greater 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 1s to 32s. the mic2846 will remember the brightness level and mode it was changed to. for proper operation, ensure that the dc pin has remained high for at least t delay (140s) before issuing a mode change command. dc brightness t prog_high t prog_low level n level n - 1 level pulse ignored level n + 1 figure 13. brightness programming pulses multiple brightness levels can be changed as shown in figure 14. when issuing multiple brightness level adjustments to the dc pin, ensure both t prog_low and t prog_high are within 1s and 32s. to maintain operation at the current brightness level simply maintain a logic level high at the dc pin. figure 14. decreasing brightness several levels as mentioned, mic2846 can be programmed to set wled drive current to produce one of 32 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. one-step brightness changes the ?one-step? brightness change procedure relieves the user from keeping trac k of the mic2846?s 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.
micrel inc. mic2845/46 january 2008 16 m9999-010808-a figure 15. 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 (1s to 32s) as shown in figure 15. 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 (1s to 32s). figure 16 illustrates the proper timing for execution of a one-step brightness increase. figure 16. one-step brightness increase presetting brightness the mic2846 does not turn on the current sinks until 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 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 first presetting pulse edge must occur somewhere between the timeframe of 35s to 50s, otherwise the mic2846 may continue to start up at the full (default) brightness level. figure 17. presetting timing figure 17 shows the correct presetting sequence to set the mic2846 brightness to level 22 prior to start up. 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 t prog_high and t prog_low pulse width must still be between 1s to 32s`.)
micrel inc. mic2845/46 january 2008 17 m9999-010808-a ldo mic2845/6 ldos are low noise 150ma ldos. the mic2845/6 ldo regulator is fu lly protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. input capacitor the mic2845/6 ldos are high-performance, high bandwidth devices. 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 mic2845/6 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 equiv alent operating temperature range. no-load stability unlike many other voltage regulators, the mic2845/6 ldos will remain stable and in regulation with no load. this is especially important in cmos ram keep-alive applications. thermal considerations the mic2845/6 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 ? 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 ? 2.8v) x 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 mic2845/6 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 ? 2.8v) x 150ma = 0.120w p ldo2 = (3.6v ? 1.5v) x 150ma = 0.315w p total =0.120w+ 0.315w = 0.435w = (125c ? t a )/(60c/w) t a = 125c ? 0.435w x 60c/w t a = 98.9c therefore, under the abov e conditions, the maximum ambient operating temperature of 98.9c is allowed.
micrel inc. mic2845/46 january 2008 18 m9999-010808-a mic2845 typical a pplication circuit bill of materials item part number manufacturer description qty. c1, c2, c3 c1608x5r0j105k tdk (1) 1f ceramic capacitor, 6.3v, x5r, size 0603 3 r1 crcw06032052ft1 vishay (2) 20.5k ? , 1%, size 0603 1 u1 mic2845-xxymt micrel, inc. (3) 6 channel pwm controlled current sink wled driver with dual ldos 1 notes: 1. tdk: www.tdk.com 2. vishay: www.vishay.com 5. micrel, inc.: www.micrel.com
micrel inc. mic2845/46 january 2008 19 m9999-010808-a mic2846 typical a pplication circuit bill of materials item part number manufacturer description qty. c1, c2, c3 c1608x5r0j105k tdk (1) 1f ceramic capacitor, 6.3v, x5r, size 0603 3 r1 crcw06032052ft1 vishay (2) 20.5k ? , 1%, size 0603 1 u1 mic2846-xxymt micrel, inc. (3) 6 channel digital controlled current sink wled driver with dual ldos 1 notes: 1. tdk: www.tdk.com 2. vishay: www.vishay.com 5. micrel, inc.: www.micrel.com
micrel inc. mic2845/46 january 2008 20 m9999-010808-a pcb layout recommendations (fixed) top layer fixed bottom layer
micrel inc. mic2845/46 january 2008 21 m9999-010808-a 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 specifications 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 significan t injury to the user. a purchaser?s use or sale of micrel produc ts for use in life support app liances, 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. ? 2008 micrel , incor p orated.

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