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MIC2843 high-efficiency 6-channel linear wled driver with ultra-fast pwm? control ultra fast pwm 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 general description the MIC2843 is a high-efficien cy linear white led (wled) driver designed to drive up to six wleds, greatly extending battery life for portable display backlighting, keypad backlighting, and camera flash in mobile devices. the MIC2843 provides the highest possible efficiency as this architecture has no switching losses present in traditional charge pumps or inductive boost circuits. the MIC2843 provides six linear drivers which maintain constant current for up to six wleds. it features a typical dropout of less than 40mv at 20ma. this allows the wleds to be driven directly from the battery eliminating switching noise/losses present with the use of boost circuitry. the six channels are matched better than 3% typical, ensuring uniform display illumination under all conditions. the brightness is controlled through an ultra fast pwm? interface operating down to less than 1% duty cycle. the MIC2843 is available in the 2mm x 2mm 10-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 ? high efficiency (no voltage boost losses) ? ultra fast pwm? control (200hz to 500khz) ? input voltage range: 3.0v to 5.5v ? dropout of less than 40mv at 20ma ? matching better than 3% (typical) ? current accuracy better than 1.5% (typical) ? maintains proper regulation regardless of how many channels are utilized ? available in a 2mm x 2mm 10-pin thin mlf ? package applications ? mobile handsets ? digital cameras ? portable media/mp3 players ? portable navigation devices (gps) ? portable applications ____________________________________________________________________________________________________________ typical application lcd display backlight with six wleds high current flash driver november 2010 m9999-110810-b
micrel inc. MIC2843 november 2010 2 m9999-110810-b ordering information part number mark code (1) temperature range package (2) MIC2843ymt ys3 ?40c to +125c 10-pin 2mm x 2mm thin mlf ? 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. pin configuration 10-pin 2mm x 2mm thin mlf ? (mt) (top view) pin description pin number pin name pin function 1 vin voltage input. connect at le ast 1f ceramic capacitor between v in and gnd. 2 end enable led drivers. this pin can be used as a pwm input for dimming of wleds. do not leave floating. 3 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. 4 gnd ground. 5 d6 led6 driver input. connect led anode to vin and cathode to this pin. 6 d5 led5 driver input. connect led anode to vin and cathode to this pin. 7 d4 led4 driver input. connect led anode to vin and cathode to this pin. 8 d3 led3 driver input. connect led anode to vin and cathode to this pin. 9 d2 led2 driver input. connect led anode to vin and cathode to this pin. 10 d1 led1 driver input. connect led anode to vin and cathode to this pin. epad hs pad heat sink pad. not intern ally connected. connect to ground.
micrel inc. MIC2843 november 2010 3 m9999-110810-b absolute maximum ratings (1) main input voltage (v in ) .................................. ? 0.3v to +6v enable input voltage (v end ) ............................ ? 0.3v to +6v current source voltage (v d1-d6 ) ..................... ? 0.3v to +6v power dissipation .....................................in ternally limited lead temperature (solde ring, 10sec .) ....................... 260c storage temperature (t s ) ......................... ? 65c to +150c esd rating (3) ................................................. esd sensitive operating ratings (2) supply voltage (v in )..................................... +3.0v to +5.5v enable input voltage (v end ) .................................. 0v to v in current source voltage (v d1-d6 ) ............................ 0v to v in junction temperature (t j ) ........................ ?40c to +125c junction thermal resistance 2mm x 2mm thin mlf ? -10l ( ja )......................90c/w electrical characteristics wled linear drivers v in = v end = 3.8v, r set = 20.5k ? ; v d1-d6 = 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 (4) v dropnom = 0.6v 1.5 % matching (5) v dropnom = 0.6v 3 5.5 % drop-out where i led = 90% of led current seen at v dropnom = 0.6v, 100% brightness level 40 100 mv ground/supply bias current i out = 20ma 1.4 ma shutdown current (current source leakage) v end = 0v 0.01 1 a pwm dimming logic low 0.2 v enable input voltage (v end ) logic high 1.2 v enable input current v ih > 1.2v 0.01 1 a current source delay (50% levels) shutdown to on standby to on on to standby r set = 20.5k 40 0.5 1 60 s s s current source transient time (10% ? 90%) t rise t fall 1 0.3 s s standby to shutdown time v end = 0v 10 20 40 ms notes: 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. handling pr ecautions recommended. human body model, 1.5k ? in series with 100pf. 4. as determined by average current of all channels in use and all channels loaded. 5. the current through each led meets the stated limits from the average current of all leds.
micrel inc. MIC2843 november 2010 4 m9999-110810-b typical characteristics
micrel inc. MIC2843 november 2010 5 m9999-110810-b typical characteristics (continued)
micrel inc. MIC2843 november 2010 6 m9999-110810-b functional characteristics
micrel inc. MIC2843 november 2010 7 m9999-110810-b functional characteristics
micrel inc. MIC2843 november 2010 8 m9999-110810-b functional diagram figure 1. MIC2843 functional block diagram
micrel inc. MIC2843 november 2010 9 m9999-110810-b functional description the MIC2843 is a six-channel wled driver. the wled driver is designed to maintain proper current regulation with led current accuracy of 1.5% while the typical matching between the six channels to be 3% at room temperature. the wleds ar e driven independently from the input supply and will maintain regulation with a dropout of 40mv at 20ma. the low dropout of the linear drivers allows the wleds to be driven directly from the battery voltage and eliminates the need for large and inefficient charge pumps. the maximum wled current for each channel is set via an external resistor. if dimming is desired the MIC2843 can dim via an ultra fast pwm? signal. block diagram as shown in figure 1, the MIC2843 consists of six current mirrors set to copy a master current determined by r set . the linear drivers have a designated control block for enabling and dimming of the wleds. the MIC2843 is controlled by t he pwm control block that receives pwm signals for dimming. vin the input supply (v in ) provides power to the linear drivers and the control circuitry. the v in operating range is 3v to 5.5v. due to wire inductance a minimum bypass capacitor of 1f 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). end the end pin is equivalent to the enable pin for the linear drivers on the MIC2843. it can also be used for dimming using a pwm signal. see the ?pwm dimming interface? in the application information section for details. the first pulse on the end pin must be equal or greater to 40s to wake the part up in a known state. this equates to a 12.5khz pwm signal at equal or greater than 50% duty cycle. higher pwm frequencies may be used but the first pulse must be equal or greater than 40s. r set the r set pin is used by connecting a r set resistor to ground to set the peak current of the linear drivers. the average led current can be calculated by equation 1 below: i led (ma) = 410 d / r set (k ? ) eq. 1 d is the duty cycle of the led current during pwm dimming. when the device is fully on the duty cycle equals 100% (d = 1). a plot of i led versus r set is shown in figure 2. figure 2. peak led current vs. r set d1-d6 the d1 through d6 pins are the linear driver 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 linear drivers are independent of each other. gnd the ground pin is the ground path for the linear drivers. the current loop for the ground should be as small as possible. 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 section for more details.
micrel inc. MIC2843 november 2010 10 m9999-110810-b application information ultra fast pwm? dimming interface figure 3. average current per led dimming by changing pwm duty cycle for pwm frequencies up to 20khz figure 4. average current per led dimming by changing pwm duty cycle for pwm frequencies from 50khz to 500khz figure 5. minimum duty cycle for varying pwm frequency the MIC2843 can receive pwm signals from the end pin for wled dimming. dimming is generated by pulsing the wleds on and off in synchronization with the pwm signal. the MIC2843 supports pwm frequencies from 200hz to 500khz. for pwm frequencies between 200hz ? 20khz the MIC2843 supports a duty cycle range from 1% to 100%. the MIC2843 supports ultra fast pwm? frequencies from 20khz to 500khz with a duty cycle of 10% and greater. MIC2843 incorporates an internal shutdown delay to ensure that the internal control circuitry remains active during pwm dimming for optimum ultra fast pwm? performance. due to input pwm signal propagation delay ultra fast pwm? signals have a non-linear relationship between the duty cycle and the average led current (figures 3 and 4). with the ultra fast pwm? frequencies, lower duty cycles may degrade the matching between leds, and should be limited to the minimum duty cycle, as indicated in figure 5. due to the shutdown-to-on delay of 60s, at ultra fast pwm? frequencies above 15khz, a logic high enable signal is required to first wake up prior to pwm dimming. figures 6 through 10 illustrate the wled current response when a pwm signal is applied to the end pin.
micrel inc. MIC2843 november 2010 11 m9999-110810-b figure 6. pwm signal at 1% duty cycle (iavg = 0.2ma) figure 7. pwm signal at 20% duty cycle (iavg = 4ma) figure 8. pwm signal at 50% duty cycle (i avg = 10ma) figure 9. pwm signal at 80% duty cycle (i avg = 16ma) figure 10. pwm signal at 100% duty cycle (i avg = 20ma)
micrel inc. MIC2843 november 2010 12 m9999-110810-b high-current parallel operation the linear drivers are independent of each other, and can be used individually or paralleled for larger current. a single wled can be driven with all six linear drivers by connecting d1 through d6 together with the cathode of the wled as shown in figure 11. this will generate a current six times the led current setting and can be used for higher current wleds such as those used in flash or torch applications. figure 11. six-channel (parallel) application circuit the current is set by the r set resistor, and can be calculated by the following equation: i led (ma) = 6 * 410 * d / r set (k ? ). d is the duty cycle of the led current during pwm dimming. when the device is fully on the duty cycle equals 100% (d = 1). figure 12 shows the response time of the six paralleled linear drivers to the enable signal, while figure 13 shows the turn off response. with a r set resistor of 1.65k, each linear driver is set to 250ma, with all 6 linear drivers connected in parallel, the MIC2843 is capable of driving a total current of 1.5a. figure 12. current response time to enable signal turning on (six pa ralleled channels) figure 13. current response time to enable signal turning off (six pa ralleled channels) input capacitor the MIC2843 is a high-performance, high-bandwidth device. 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 therefore, not recommended.
micrel inc. MIC2843 november 2010 13 m9999-110810-b MIC2843 typical a pplication circuit bill of materials item part number manufacturer description qty. c1 c1608x5r0j105k tdk (1) 1f ceramic capacitor, 6.3v, x5r, size 0603 1 r1 crcw06032052ft1 vishay (2) 20.5k ? , 1%, size 0603 1 u1 MIC2843ymt micrel, inc. (3) high-efficiency six-channel linear wled driver with ultra-fast pwm? control 1 notes: 1. tdk: www.tdk.com . 2. vishay: www.vishay.com . 3. micrel, inc.: www.micrel.com .
micrel inc. MIC2843 november 2010 14 m9999-110810-b pcb layout recommendations top layer bottom layer
micrel inc. MIC2843 november 2010 15 m9999-110810-b package information 10-pin (2mm x 2mm) 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 micrel makes no representations or warranties with respect to t he accuracy or completeness of the information furnished in this data sheet. this information is not intended as a warranty and micrel does not assume responsibility for it s use. micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. no license, whether expre ss, implied, arising by estoppel or other wise, to any intellectual property rights is granted by this document. except as provided in micrel?s terms and conditions of sale for such products, mi crel assumes no liability whatsoever, and micrel disclaims any express or implied warranty relating to the sale and/or use of micrel products including l iability or warranties relating to fitness for a particular purpose, merchantability, or infringement of an y patent, copyright or other intellectual p roperty right 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 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 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 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. can nt ? 2008 micrel, incorporated. .

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