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atmel led drivers MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input datasheet brief
2 atmel led drivers-MSL2041/2042 general description the atmel ? led drivers- MSL2041 and msl2042 compact, high-power led string controllers use external current control mosfets to sink up to 1a per string, with string current matching of 0.5%. the MSL2041/2 drive four parallel strings of leds and offer fault detection and management of open circuit and short circuit leds. the MSL2041 features four pwm inputs that allow independent frequency, dimming and phasing of each string, while the msl2042 offers one pwm input for frequency and dimming control of all four strings, and automatically phase shifts the string drive signals. peak string currents are set using current sense (fet source) resistors and adjustable with an internal 8-bit dac. atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input the MSL2041/2 adaptively control up to two dc-dc converters that power the led strings, using atmel's adaptive sourcepower? technology. these efficiency optimizers minimize power use while maintaining led current accuracy. multiple MSL2041/2s cascade to automatically negotiate the optimum power supply voltage when driving more than four strings from a single power supply. the MSL2041/2 features fault control for open-circuit strings, led short- circuits and device over-temperature conditions. when a string open-circuit or led short-circuit condition is detected, the MSL2041/2 turn off the faulty string and pull the open-drain fault output low. the MSL2041/2 feature stand-alone operation, and the basic circuit requires just one to four external pwm dimming inputs. an i 2 c serial interface is provided to allow optional control and monitoring of the various fault detection and adaptive sourcepower parameters, but is not required for operation. the MSL2041/2 are offered in the 32-pin, 300mil sop package, and operate over the -40c to +85c temperature range. applications ? lcd-tvs ? pc monitors ? industrial displays ? general illumination ? street-lighting ? post-regulated or offline powered led strings ordering information part no. pwm inputs auto-phase delay package MSL2041gu 4 no 32 pin, 300mil sop msl2042gu 1 yes 32 pin, 300mil sop
3 atmel led drivers-MSL2041/2042 atmel led drivers-MSL2041/msl2042 atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input key features application circuit ? drives four parallel high power led strings ? up to 1a led string current with external n-channel mosfets ? operates stand-alone, basic circuit needs only pwm input(s) ? four pwm inputs allow individual frequency, brightness and phase control of each led string (MSL2041) ? one pwm input controls the frequency and brightness of the automatically phase shifted strings (msl2042) ? 8-bit adaptive sourcepower ? correction optimizes string power supply for maximum efficiency ? multiple MSL2041/2s share a string supply and automatically negotiate the optimum supply voltage ? 0.5% current matching between strings ? string open-circuit and led short-circuit fault detection and protection ? external mosfets offer flexibility of leds used in each string ? i 2 c serial interface allows optional control of device functions and faults ? 32-pin 300mil sop package ? -40c to +85c operating temperature range ? lead-free, halogen-free, rohs compliant package
4 atmel led drivers-MSL2041/2042 package and pinout C sop package dimensions: 32 pin 20.52mm x 7.49mm x 2.49mm sop (1.27mm pin pitch) ? ? f b o 1 1 3 2 f b i 1 f b o 1 1 3 2 f b i 1 e n 2 3 1 f b o 2 e n 2 3 1 f b o 2 p w m 3 3 3 0 f b i 2 c g n d 3 3 0 f b i 2 p w m 2 4 2 9 g n d c g n d 4 2 9 g n d p w m 1 5 2 8 v i n c g n d 5 2 8 v i n p w m 0 6 2 7 vcc p w m 0 6 2 7 vcc f l t b 7 2 6 cvdd f l t b 7 2 6 cvdd scl 8 2 5 vdd scl 8 2 5 vdd sda 9 2 4 n c sda 9 2 4 n c d 0 1 0 2 3 d 3 d 0 1 0 2 3 d 3 g 0 1 1 2 2 g 3 g 0 1 1 2 2 g 3 s 0 1 2 msl 2041 ( t o p v i e w ) 2 1 s 3 s 0 1 2 msl 2 0 4 2 ( t o p v i e w ) 2 1 s 3 d 1 1 3 2 0 s 2 d 1 1 3 2 0 s 2 g 1 1 4 1 9 g 2 g 1 1 4 1 9 g 2 s 1 1 5 1 8 d 2 s 1 1 5 1 8 d 2 n c 1 6 1 7 n c n c 1 6 1 7 n c
5 atmel led drivers-MSL2041/2042 pin descriptions pin name description MSL2041 msl2042 1 1 fbo1 effciency optimizer feedback output 1 connect fbo1 to the feedback node of the frst external string power supply through a diode, or to fbi1 of the next device when operating the devices in a chain confguration. if unused, leave fbo1 unconnected. 2 2 en enable input (active high) drive en high to turn on the MSL2041/2, drive it low to turn off the MSL2041/2. for automatic startup connect en to vin through a 100k resistor. toggle en low to release fltb and to return any and all registers to their power-up default values. 3 - pwm3 pwm dimming input 3 drive pwm3 with a pulse-width modulated signal to control the brightness of string three. if unused, connect pwm3 to ground. 4 - pwm2 pwm dimming input 2 drive pwm2 with a pulse-width modulated signal to control the brightness of string two. if unused, connect pwm2 to ground. 5 - pwm1 pwm dimming input 1 drive pwm1 with a pulse-width modulated signal to control the brightness of string one. if unused, connect pwm1 to ground. 6 6 pwm0 pwm dimming input 0 drive pwm0 with a pulse-width modulated signal to control the brightness of string zero (MSL2041) or all strings (msl2042). 7 7 fltb fault indication output (open drain, active low) fltb sinks current to gnd whenever the MSL2041/2 detects and verifes a fault condition. toggle en low (or read the fault registers) to clear fltb. 8 8 scl i2c serial clock input scl is the i2c serial interface clock input. 9 9 sda i2c serial data i/o sda is the i2c serial interface bi-directional data line. 10 10 d0 drain sense input 0 drain sense input for external mosfet 0. connect d0 through a resistor to the drain of the external mosfet driving led string 0. if unused, connect d0 to ground. 11 11 g0 gate output 0 gate drive output for external mosfet 0. connect g0 to the gate of the external mosfet driving led string 0. if unused, connect g0 to ground. 12 12 s0 source sense input for string 0 connect s0 to the source of the external mosfet, and to the current sense resistor for led string 0. the full scale led current is reached when 500mv is across the current sense resistor. if unused, connect s0 to vdd. 13 13 d1 drain sense input 1 drain sense input for external mosfet 1. connect d1 through a resistor to the drain of the external mosfet driving led string 1. if unused, connect d1 to ground. 14 14 g1 gate output 1 gate drive output for external mosfet 1. connect g1 to the gate of the external mosfet driving led string 1. if unused, connect g1 to ground. 15 15 s1 source sense input for string 1 connect s1 to the source of the external mosfet, and to the current sense resistor for led string 1. the full scale led current is reached when 500mv is across the current sense resistor. if unused, connect s1 to vdd 16, 17, 24 16, 17, 24 nc no internal connection nc is not internally connected . 18 18 d2 drain sense input 2 drain sense input for external mosfet 2. connect d2 through a resistor to the drain of the external mosfet driving led string 2. if unused, connect d2 to ground. atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
6 atmel led drivers-MSL2041/2042 pin name description MSL2041 msl2042 19 19 g2 gate output 2 gate drive output for external mosfet 2. connect g2 to the gate of the external mosfet driving led string 2. if unused, connect g2 to ground. 20 20 s2 source sense input for string 2 connect s2 to the source of the external mosfet, and to the current sense resistor for led string 2. the full scale led current is reached when 500mv is across the current sense resistor. if unused, connect s2 to vdd. 21 21 s3 source sense input for string 3 connect s3 to the source of the external mosfet, and to the current sense resistor for led string 3. the full scale led current is reached when 500mv is across the current sense resistor. if unused, connect s3 to vdd. 22 22 g3 gate output 3 gate drive output for external mosfet 3. connect g3 to the gate of the external mosfet driving led string 3. if unused, connect g3 to ground. 23 23 d3 drain sense input 3 drain sense input for external mosfet 3. connect d3 through a resistor to the drain of the external mosfet driving led string 3. if unused, connect d3 to ground. 25 25 vdd 2.5v internal ldo regulator output vdd powers internal logic. bypass vdd to gnd with a 2.2f ceramic capacitor placed close to vdd. 26 26 cvdd connect to vdd connect cvdd to vdd. 27 27 vcc 5v internal ldo regulator output vcc powers internal logic. bypass vcc to gnd with a 2.2f ceramic capacitor placed close to vcc. 28 28 vin supply voltage input connect a 12v 10% supply to vin. bypass vin to gnd with a 1.0f ceramic capacitor . 29 29 gnd power ground connect gnd to system ground. 30 30 fbi2 effciency optimizer feedback input 2 connect fbi2 to fbo2 of the previous device when using the devices in a chain confguration. if unused, connect fbi2 to ground. 31 31 fbo2 effciency optimizer feedback output 2 connect fbo2 to the feedback node of the second external string power supply through a diode, or to fbi2 of the next device when operating the devices in a chain confguration. if unused, leave fbo2 unconnected. 32 32 fbi1 effciency optimizer feedback input 1 connect fbi1 to fbo1 of the previous device when using the devices in a chain confguration. if unused, connect fbi1 to ground. - 3, 4, 5 cgnd connect to ground connect all cgnd pins to gnd as close to the msl2042 as possible.
7 atmel led drivers-MSL2041/2042 absolute maximum ratings voltage - with respect to gnd (sop), ep/gnd (tqfn) vin, en, g0 - g3 ................................................................................................................................................................................ -0.3v to +16v d0 - d3 ...................................................................................................................................................................................................... -0.3v to +24v vdd, cvdd ........................................................................................................................................................................................... -0.3v to +2.75v vcc ................................................................................................................................................................................................................. -0.3v to +5.5v sda, scl, pwm0 - pwm3 ....................................................................................................................................................... -0.3v to +5.5v fbi1, fbi2, fbo1, fbo2, fltb ......................................................................................................................... -0.3v to (vcc + 0.3v) current - (into pin) vin ....................................................................................................................................................................................................................................... 50ma gnd .................................................................................................................................................................................................................................. 500ma d0 - d3 ................................................................................................................................................................................................................................ 1ma all other pins ................................................................................................................................................................................................................. 20ma continuous power dissipation at 70c 32-pin sop (derate 28.7mw/c above t a = +70c) .................................................................................................. 1576mw ambient operating temperature range t a = t min to t max .................................................................. -40c to +85c junction temperature .................................................................................................................................................................................... +125c storage temperature range ............................................................................................................................................ -65c to +125c lead soldering temperature, 10s ....................................................................................................................................................... +300c atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
8 atmel led drivers-MSL2041/2042 parameter symbol conditions min typ max unit dc electrical characteristics vin operating supply voltage 10.8 12.0 13.2 v vin operating supply current all drivers driven, i2c serial interface idle 19.2 31.5 ma vin sleep supply current i2c serial interface idle, sleep = 1 2.9 4.2 ma vin shutdown supply current en = 0, all digital inputs = vdd or gnd 0.1 2 a vdd regulation voltage 2.25 2.5 2.75 v input high voltage pwm0 - pwm3, scl, sda 0.7 x vdd v input low voltage pwm0 - pwm3, scl, sda 0.3 x vdd v en input high voltage 1.9 en input low voltage 1.0 v en input hysteresis 150 mv sda, fltb output low voltage sinking 3ma 0.5 v open circuit string fault detect voltage oc ref 6 v short circuit string fault detect voltage sc ref 6 v d0 - d3 leakage current voltage under 9v 0.1 a voltage between 9v to 16v 5 a g0 - g3 maximum gate drive voltage 9.0 9.6 10.2 v g0 - g3 gate drive current pwmn = vdd; sn = gnd; gn = gnd 109 ma g0 - g3 gate sink current pwmn = gnd; gn = 9.6v -18 ma current sense regulation voltage istr0 = 0xff; t a = 25c 465 490 498.75 mv istr0 = 0xff; t a = 85c 455.7 524.3 mv istr0 = 0x7f; t a = 25c 242.5 250 257.5 mv istr0 = 0x7f; t a = 85c 235 265 mv string-to-string current matching istr0 = 0x7f; t a = 25c 0.50 2.2 % istr0 = 0x7f; t a = -40c to +85c 0.75 3.2 thermal cut-off temperature 135 c fbin to fbon current transfer error fbin = 100ua 2 % fbon current step-size 1.1 a fbon feedback output current maximum compliance voltage 3.5v minimum 210 a electrical characteristics vin = 12v, t a = t min to t max , unless otherwise noted. typical values are at vin = 12v, t a = +25c. parameter symbol conditions min typ max unit ac electrical characteristics pwm frequency f pwm (note 7) 0 50,000 hz pwm duty cycle (note 7) 0 100 %
9 atmel led drivers-MSL2041/2042 note 1. minimum scl clock frequency is limited by the bus timeout feature, which resets the serial bus interface if either sda or scl is held low for t timeout . note 2. t vd:ack = scl low to sda (out) low acknowledge time. note 3. t vd:dat = minimum sda output data-valid time following scl low transition. note 4. a master device must internally provide an sda hold time of at least 300ns to ensure an scl low state. note 5. the maximum sda and scl rise times is 300ns. the maximum sda fall time is 250ns. this allows series protection resistors to be connected between sda and scl inputs and the sda/scl bus lines without exceeding the maximum allowable rise time. note 6. MSL2041/2 includes input filters on sda and scl that suppress noise less than 50ns. note 7. parameter is guaranteed by design and not production tested. parameter symbol conditions min typ max unit i2c switching characteristics scl clock frequency 1/t scl bus timeout disabled (note 1) 0 1,000 khz stop to start condition bus free time t buf 0.5 s repeated start condition hold time t hd:sta 0.26 s repeated start condition setup time t su:sta 0.26 s stop condition setup time t su:stop 0.26 s sda data hold time t hd:dat 5 ns sda data valid acknowledge time t vd:ack (note 2) 0.05 0.55 s sda data valid time t vd:dat (note 3) 0.05 0.55 s sda data set-up time t su:dat 100 ns scl clock low period t low 0.5 s scl clock high period t high 0.26 s sda, scl fall time t f (note 4, note 5) 120 ns sda, scl rise time t r 120 ns sda, scl input suppression filter period t sp (note 6) 50 ns atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
10 atmel led drivers-MSL2041/2042 block diagram figure 1. atmel led drivers-MSL2041/2 block diagram
11 atmel led drivers-MSL2041/2042 typical application circuit figure atmel ed drivers-ms driving four ed strings at ma peak current per string controlling a single power supply atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
12 atmel led drivers-MSL2041/2042 the MSL2041 and msl2042 are highly integrated, flexible, four-string led drivers that use external mosfets to allow high string currents, and include power supply control to maximize efficiency of up to two external string power supplies. optimized for stand-alone operation they require only external pwm signal(s), a few external components (including the string drive n-channel mosfets) and an external string power supply. the MSL2041/2s four mosfet gate drive outputs, g0 - g3, are optimized to drive fets with a maximum gate voltage threshold of 3v. the MSL2041/2 led drivers provide simple control of led brightness through both peak current and external pwm drive controls. peak current control, set by external fet source resisters, offers excellent color consistency, while pulse width control allows simple brightness management. multiple devices easily connect together to drive more than four led strings while maintaining optimum system efficiency. an active low fault output activates when either a string open circuit or an led short circuit condition is detected and verified. the MSL2041/2 are intended for stand-alone operation but offer additional string control and monitoring through a 1mhz i 2 c/smbus compatible serial interface. use of the serial interface is not required for operation. the MSL2041 offers four pwm inputs that directly control the four string drive outputs, while the msl2042 requires only a single pwm input signal and features automatic, progressive phase spreading of the four string drive signals. with phase spreading a ? pwm frame time delay is calculated and applied progressively to the string drive signals. phase spreading helps reduce both the transient load on the led power supply, and the power supply output capacitor size requirement. the adaptive sourcepower efficiency optimizer (eo) outputs control a wide range of different architectures of external dc/dc and ac/dc converters. multiple drivers in a system communicate with each other in real time to select an optimized operating voltage for the leds. the eo allows design of the power supply for the worst case forward voltage (v f ) of the leds without worrying about excessive power dissipation issues, while ensuring that the led drive system is operating at optimum efficiency. during start-up the eo automatically reduces the string power supply voltage to the minimum value required to keep the leds in current regulation. the eo periodically performs re-optimization to compensate for changes of the leds forward voltage, and to assure continued optimum power savings. additionally, all string drivers are continually monitored for proper operation, and if any of the led strings become starved for current the efficiency optimizer automatically increases the string power supply voltage to bring the string back in to current regulation. setting the maximum led string current with the fet source resistor r s the maximum string current, i led , for each string is set by a shunt resistor, r s , connected to ground from the source terminal of the string drive mosfet (figure 1, page 6). determine the resistor value using ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = led s i r 50196 . 0 255 127 (where 127 is the default value of istr, string current control register 0x0e). for example, a full-scale led current of 350ma returns r s = 0.715 (to the nearest 1% resistor value). led string fault response the MSL2041/2 monitor the led strings to detect led short-circuit and string open-circuit faults (figure 3). when verified, all string faults force the open drain fault output fltb low. after power-up, when shorted leds are verified in a string the string is disabled and no longer monitored by the efficiency optimizer. the short circuit threshold is 6v (typical) and the additive voltage drop lost from the shorted leds, plus the headroom required for the external fet, must be equal to or greater than the 6v threshold to generate a fault. typically, two leds in a string must be shorted to cause a short circuit fault, detailed description
13 atmel led drivers-MSL2041/2042 but because leds differ, the number of shorted leds required to generate a fault varies. the current fold-back option, available through the serial interface, slightly changes the fault response when an led short circuit event is suspected. a string with an open circuit led is off by default, and when this situation is verified the faulty string is disabled and no longer monitored by the efficiency optimizer. toggling en low and then high clears all faults and the MSL2041/2 begin to control and monitor all strings as if experiencing an initial power-up. fault conditions that persist re-establish fault responses. faulty strings are flagged in the fault registers. when using the serial interface, fault conditions are typically read in response to fltb pulling low. f i gur e 3 . o p e n - c i r c u it a nd s hor t - c i r c u it d e t ection b l o ck d i a g r a m figure 3. open-circuit and short-circuit detection block diagram over temperature shutdown the MSL2041/2 includes an automatic over- temperature shutdown. if the die temperature exceeds 135c, the device turns off, just as if the enable input en is forced low. when the die temperature drops below 120c the device wakes up again and turns on as if experiencing an initial power-up. connecting the efficiency optimizer to an led string power supply and selecting resistors the MSL2041/2 are designed to control led string power supplies that use a voltage divider (r top and r bottom in figure 4) to set output voltage, and whose regulation feedback voltage is not more than 3.5v - v f . the efficiency optimizer improves power efficiency by injecting a current of between 0a and 280.5a into the voltage divider of the external power supply, dynamically adjusting the power supplys output to the minimum voltage required by the led strings. each of the two eos monitors two led strings. strings zero and one are assigned to fbo1, and strings two and three are assigned to fbo2 (table 1). when a single supply is used for all four strings connect fbo2 to fbi1 (figure 4), as explained in the next section using multiple eos/devices to control a common power supply . the MSL2041/2 then automatically maximizes efficiency for all strings. when two supplies are used, connect fbo1 to the supply powering strings zero and one, and connect fbo2 to the supply powering strings two and three (figure 5). for clarity, figure 4 and figure 5 do not show the source and drain connections between the devices and the mosfets. atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
14 atmel led drivers-MSL2041/2042 table 1. string eo assignments figure 4. eo configuration when using a single string power supply
15 atmel led drivers-MSL2041/2042 figure 5. eo configuration when using two string power supplies atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
16 atmel led drivers-MSL2041/2042 to select r top and r bottom first determine v out(min) and v out(max) , the minimum and maximum string supply voltage limits, using: v out(min) = ( v f (min) * [#ofleds] ) + 0.5 , and v out(max) = ( v f (max) * [#ofleds] ) + 0.5 , where v f(min) and v f(max) are the leds minimum and maximum forward voltage drops at the peak current set by r s . for example, if the led data are v f(min) = 3.5v and v f(max) = 3.8v, and ten leds are used in a string, then the total minimum and maximum voltage drop across a string is 35v and 38v. adding an allowance of 0.5v for the string drive mosfet headroom brings v out(min) to 35.5v and v out(max) to 38.5v. then determine r top using: ) ( ) ( ) ( max fbon min out max out top i v v r ? = , where i fbon(max) is the 280.5a maximum output current of the efficiency optimizer outputs fbon (280.5a = 1.1a * 255, the current per lsb of the fbo dac times the maximum dac count). finally, determine r bottom using: r bottom = r top * v fb , v out(max) _ v fb where v fb is the regulation feedback voltage of the power supply. place a diode (1n4148 or similar) between fbon and the supplys feedback node to protect the MSL2041/2 against current flow into fbon. once configured, determine the change in power supply output voltage in response to a change in fbon output current using: top fbon out r i v ? ? = ? . assure that the power supply settling time for a voltage step size of 1.1a * r top is less than the 4ms eo step-hold duration time. using multiple eos/devices to control a common power supply cascade multiple efficiency optimizers (eos), either within the same device or across multiple devices, into a chain configuration (figure 6), with the fbin of one eo connected to the fbon of the next. connect the first fbon to the power supply feedback resistor node through a diode (1n4148 or similar) placed close to the power supply feedback node, and unused fbin inputs to ground as close to the MSL2041/2 as possible. the chained eos work together to ensure that the system operates at optimum efficiency. note that the accuracy of the feedback chain may degrade through each link of the fbin/fbon chain by 2% (typical). derate the maximum fbon current using: i fbo(max / min) = 280.5a* (0.98) n -1 , where n is the number of eos connected in series. use i fbon(max/min) in the above r top resistor equation for the term i fbon(max) instead of using 280.5a. take care in laying out the traces for the efficiency optimizer connections. minimize the fbin/fbon trace lengths as much as possible. do not route the signals close to traces with large variations in voltage or current, because noise may couple into fbin. if these traces must be routed near noisy signals, shield them from noise by using ground planes or guard traces. for clarity, figure 6 shows source and drain connections only for unused outputs 2 and 3 of device two. note that because of the interplay between eos and the automatic fault response behavior, when both strings monitored by a single eo fault and turn off, that the string supply is forced to its maximum value and all remaining active strings typically detect short circuit faults and also turn off.
17 atmel led drivers-MSL2041/2042 figure 6. eo chain configuration of two devices, six strings and a single string power supply atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
18 atmel led drivers-MSL2041/2042 choosing the drain resistor r d the drain resistor r d connects the MSL2041/2 to the drain of the external mosfet. choose r d using: , where v out(max) is the value calculated above in the section connecting the efficiency optimizer to an led string power supply and selecting resistors beginning on page12, n is the number of leds in the string, i dark is the maximum allowable string off current and v f(dark) is the led forward voltage drop at i dark . when the value calculated for r d < 0 use 0 . led manufacturers typically do not publish i dark and v f(dark) information. one way to determine these numbers is to use the following method. set up the test circuit of figure 7. adjust r1 until the current meter indicates i dark (choose i dark < 1ma). use a volt meter to measure the voltage at the anode of the led (a), and then at the cathode of the led (b). subtract the voltage measured at b from that measured at a to determine v f(dark) . some typical values determined using this method are listed in table 2. f i gur e 7 . t est c i r c u it fo r d e t e r m i n i ng figure 7. test circuit for determining v f(dark) table 2. some typical i dark and v f(dark) values determined using figure 7 led type led part # i dark (a) f(dark) (v) power 1.72 2.285 medium power 1.67 2.276 high power lxlw-pwc1 1.72 2.195 large values of r d may cause false led short circuit faults. discharge of the parasitic capacitance at the dn node through a large r d holds the node above the string fault threshold for longer than the led short circuit verification time. the addition of a feed-forward capacitor, c ff in figure 8, mitigates this issue. the value for c ff depends upon the amount of parasitic capacitance at the dn node and the size of r d , but c ff = 15pf is an appropriate first approximation. f i gur e 8 . f eed for w a r d c a p acito r figure 8. feed forward capacitor
19 atmel led drivers-MSL2041/2042 direct pwm control of the led strings an external pwm signal applied to the inputs pwm0 - pwm3 (MSL2041) or pwm0 (msl2042) allows direct control over the strings frequency and duty cycle. the pwm inputs recognize signals of dc to 50khz, and 0% to 100% duty cycle. the msl2042, which allows only a single pwm input, calculates and applies a progressive delay of 1/4 th the pwm frame successively to strings one - three, while string zero follows the pwm input directly. register map summary control the MSL2041/2 using the registers in the range 0x00 - 0x18. register bit values always revert to their default values (table 4) when en is taken high. do not write to registers not listed in table 3. table 3. register map address and register name function register data d7 d6 d5 d4 d3 d2 d1 d0 0x00 stringen led string enable - - - - str3en str2en str1en str0en 0x01 unused 0x02 config confguration fldbken i 2 ctoen - - strscfen strocfen fboen sleep 0x03 fltstatus* fault status - - - - strscdet strocdet - fltbdrv 0x04 - 0x07 unused 0x08 fltmask string fault enable - - - - fltmask3 fltmask2 fltmask1 fltmask0 0x09 scstat* led short circuit fault - - - - sc3 sc2 sc1 sc0 0x0a ocstat* string open circuit fault - - - - oc3 oc2 oc1 oc0 0x0b - 0x0d unused 0x0e istr 8-bit global string current istr[7:0] 0x0f unused 0x10 reserved must be 0x04 0 0 0 0 0 1 0 0 0x11 fboctrl effciency optimizer control fbostep[1:0] hdrmstep[1:0] - - acalen ichkdis 0x12 - 0x13 unused 0x14 fbodac1* effciency optimizer dac readback fbodac1[7:0] 0x15 fbodac2* fbodac2[7:0] 0x16 - 0x17 unused 0x18 fbostat* fbo status - - fbigndstat[1:0] - - - - * read only registers atmel led drivers-MSL2041/msl2042 low-cost, simple 4-string led drivers with external current sink mosfets, 5000:1 dimming range and per string pwm input
atmel corporation 2325 orchard parkway san jose, ca 95131 usa tel: (+1)(408) 441-0311 fax: (+1)(408) 487-2600 www.atmel.com ? 2011 atmel corporation. all rights reserved. / rev.: mem-MSL2041/42db1-e-us_06-11 atmel ? , logo and combinations thereof, and others are registered trademarks or trademarks of atmel corporation or its subsidiaries. other terms and product names may be trademarks of others. disclaimer: the information in this document is provided in connection with atmel products. no license, express or implied, by estoppel or otherwise, to any intellectual property right is granted by this document or in connection with the sale of atmel products. except as set forth in the atmel terms and conditions of sales located on the atmel website, atmel assumes no liabili ty whatsoever and disclaims any express, implied or statutory warranty relating to its products including, but not limited to, the implied warranty of merchantability, fitness for a particular purpo se, or non-infringement. in no event shall atmel be liable for any direct, indirect, consequential, punitive, special or incidental damages (including, without limitation, damages for loss and profits, business interruption, or loss of information) arising out of the use or inability to use this document, even if atmel has been advised of the possibility of such damages. atmel makes no representatio ns or warranties with respect to the accuracy or completeness of the contents of this document and reserves the right to make changes to specifications and products descriptions at any time without notice. atmel does not make any commitment to update the information contained herein. unless specifically provided otherwise, atmel products are not suitable for, and shall not be used in, automotive applications. atmel products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life. atmel asia limited unit 01-5 & 16, 19f bea tower, millennium city 5 418 kwun tong road kwun tong, kowloon hong kong tel: (+852) 2245-6100 fax: (+852) 2722-1369 atmel munich gmbh business campus parkring 4 d-85748 garching b. munich germany tel: (+49) 89-31970-0 fax: (+49) 89-3194621 atmel japan 9f, tonetsu shinkawa bldg. 1-24-8 shinkawa chuo-ku, tokyo 104-0033 japan tel: (+81)(3) 3523-3551 fax: (+81)(3) 3523-7581 register power-up defaults register power-up default values are shown in table 4. table 4. register power-up defaults register name and address power-up condition registers initialized from e2prom register data d7 d6 d5 d4 d3 d2 d1 d0 hex 0x00 stringen all four led string drive outputs enabled 0 0 0 0 1 1 1 1 0f 0x02 config device awake effciency optimizer outputs enabled string open circuit detection enabled led short circuit detection enabled i 2 c timeout enabled string current fold-back disabled 0 1 0 0 1 1 1 0 4e 0x08 fltmask all four strings monitored for faults 0 0 0 0 1 1 1 1 0f 0x0e istr global string peak current is ? its programmable value 0 1 1 1 1 1 1 1 7f 0x10 reserved 0x04 0 0 0 0 0 1 0 0 04 0x11 fboctrl mosfet current sink error detection enabled effciency optimizer auto-recalibration enabled effciency optimizer initial calibration step size = 1 lsbs effciency optimizer headroom correction step size = 1 lsbs 0 0 0 1 0 0 1 0 1a

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