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description the A6264 is a linear, programmable current regulator providing up to 100 ma from each of four outputs to drive arrays of high brightness leds. the led current can be switched between high current and low current for stop/tail applications. the two led current levels from each output, accurate to 5%, are set by two reference resistors. current matching in each string is better than 10% without the use of ballast resistors. driving leds with constant current ensures safe operation with maximum possible light output. for automotive applications, optimum performance is achieved when driving 4 strings with 1 to 3 leds in each string, at a total current of up to 100 ma in each string. outputs can be connected in parallel or left unused as required. short detection is provided to protect the leds and the A6264 during a short-to-ground at any led output pin. an open led in any of the strings disables all outputs but can be overridden. shorted led output pins or open leds are indicated by a fault flag. a temperature monitor is included to reduce the led drive current if the chip temperature exceeds a thermal threshold. the device packages are a 10-pin msop (ly) and a 16-pin tssop (lp), both with exposed pad for enhanced thermal dissipation. they are lead (pb) free, with 100% matte tin leadframe plating. A6264-ds features and benefits ? total led drive current up to 400 ma ? current shared equally up to 100 ma by up to 4 strings ? 6 to 50 v supply ? low dropout voltage ? led output short-to-ground and thermal protection ? enable input for pwm control ? current slew rate limit during pwm ? current set by reference resistor ? automotive k-temperature range version (?40c to 150c): contact factory for availability applications: typical application diagram A6264 automotive stop/tail led array driver ? automotive tail, stop, and turn lights A6264 + ? la1 vin automotive 12 v power net gnd la2 la3 la4 full ff stop switch tail switch irefh iref packages not to scale 10-pin msop with exposed thermal pad (suffix ly) 16-pin tssop with exposed thermal pad (suffix lp) www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 2 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com absolute maximum ratings 1 characteristic symbol notes rating unit load supply voltage v in ?0.3 to 50 v pin full ?0.3 to 50 v pins la[1:4] ?0.3 to 50 v pin ff ?0.3 to 50 v pins iref, irefh ?0.3 to 6.5 v ambient operating temperature range 2 t a k temperature range ?40 to 125 c maximum continuous junction temperature t j (max) 150 c transient junction temperature t tj over temperature event not exceeding 10 s, lifetime duration not exceeding 10 h, guaranteed by design characterization 175 c storage temperature range t stg ?55 to 150 c esd rating, human body model aec q100-002 all pins 2000 v esd rating, charged device model aec q100-011 corner pins 750 v aec q100-011 all other pins 500 v 1 with respect to gnd. 2 limited by power dissipation. selection guide part number ambient operating temperature, t a (c) packing package A6264klptr-t ?40 to 125 contact factory 16-pintssop with exposed thermal pad, 4.4 5 mm case A6264klytr-t ?40 to 125 4000 pieces per 13-in. reel 10-pin msop with exposed thermal pad 3 3 mm case thermal characteristics* may require derating at maximum conditions, see application information characteristic symbol test conditions* value unit package thermal resistance (junction to ambient) r ja lp package on 4-layer pcb based on jedec standard 34 oc/w on 2-layer pcb with 3.8 in. 2 of copper area each side 43 oc/w ly package on 4-layer pcb based on jedec standard 48 oc/w on 2-layer pcb with 3 in. 2 of copper area each side 85 oc/w package thermal resistance (junction to pad) r jp 2 oc/w *to be verified by characterization. additional thermal information available on the allegro ? website. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 3 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com terminal list table number name function lp ly 1,2,8,9, 15,16 ? nc no connection 3 1 irefh high current reference 4 2 iref base current reference 5 3 gnd ground reference 6 4 la1 led anode (+) connection 1 7 5 la2 led anode (+) connection 2 10 6 la3 led anode (+) connection 3 11 7 la4 led anode (+) connection 4 12 8 vin supply 13 9 full full/reduced current select 14 10 ff fault output ? ? pad exposed thermal pad la1 vin vbat current regulators gnd pad fault control te m p comp te m p monitor slew limit base current reference high current reference la2 la3 la4 irefh ff iref r ref r refh full functional block diagram pin-out diagrams lp package ly package irefh iref gnd la1 la2 ff full vin la4 la3 1 2 3 4 5 10 9 8 7 6 pad nc nc irefh iref gnd la1 la2 nc nc nc ff full vin la4 la3 nc 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 pad www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 4 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com supply and reference v in functional operating range 2 6 ? 50 v v in quiescent current i inq la[1:4] connected to vin ? ? 10 ma startup time t on vin > 7 v to i la1 < ?5 ma, r ref = 125 , full = low 51530 s current regulation reference voltage v irefx 0.7 ma < i refx < 8.8 ma 1.15 1.2 1.25 v reference current ratio g h i lax / i refi , i refi = i ref + i refh ? 12.5 ? ? current accuracy 3 e ilax ?10 ma > i lax > ?100 ma ?5 4 5 % current matching 4 e imlax ?20 ma > i lax > ?100 ma, v lax match to within 1 v ? 5 10 % output current, low level i lax(l) full = low ? g h i ref ?? i ref = 8 ma, full = low ?105 ?100 ?95 ma output current, high level i lax(h) full = high ? g h (i ref + i refh) ?? i ref = i refh = 4 ma, full = high ?105 ?100 ?95 ma maximum output current i laxmax i ref = i refh = 4.6 ma, full = high ? ? ?110 ma minimum drop-out voltage v do v in ? v lax , i lax = ?100 ma ? ? 800 mv v in ? v lax , i lax = ?40 ma ? ? 550 mv output disable threshold v odis v in ? v lax 75 ? 180 mv current slew time current rising or falling between 10% and 90% 50 80 110 s logic ff and full pins input low voltage v il ? ? 0.8 v input high voltage v ih 2?? v input hysteresis (full pin) v ihys 150 350 ? mv pull-down resistor (full pin) r pd ?50? k ff pin output low voltage v ol i ol = 1 ma ? ? 0.4 v protection short detect voltage v scd measured at lax 1.2 ? 1.8 v short circuit source current i scs short present lax to gnd ?2 ?0.8 ?0.5 ma short release voltage v scr measured at lax ? ? 1.9 v short release voltage hysteresis v schys v scr ? v scd 200 ? 500 mv open load detect voltage v ocd v in ? v lax 200 ? 500 mv open load detect delay t ocd ?2?ms thermal monitor activation temperature t jm t j with i sen = 90% 95 115 130 c thermal monitor slope a tm i sen = 50% ?3.5 ?2.5 ?1.5 %/c thermal monitor low current temperature t jl t j at i sen = 25% 120 135 150 c overtemperature shutdown t jf temperature increasing ? 170 ? c overtemperature hysteresis t jhys recovery = t jf ? t jhys ?15? c 1 for input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin. 2 function is correct but parameters are not guaranteed outside the general limits (7 to 40 v). 3 when full = low, e ilax = 100 [( | i lax | r ref / 15 ) ?1] ; when full = high, e ilax = 100 { | i lax | [(r ref r refh ) / (15 r refi )] ?1} with i lax in ma and r ref in k . 4 e imla = 100 [ max ( | i lax ? i la(av) | ) / i la(av) ] , where i la(av) is the average current of all active outputs. electrical characteristics 1 valid at t j = ?40c to 150c, v in = 7 to 40 ; unless otherwise noted characteristics symbol test conditions min. typ. max. unit www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 5 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com functional description the A6264 is a linear current regulator that is designed to pro- vide drive current and protection for parallel strings of series- connected high brightness leds in automotive applications. it provides up to four matched programmable current outputs, at up to 100 ma, with low minimum dropout voltages below the main supply voltage. for 12 v power net applications optimum performance is achieved when driving 4 strings of 1 to 3 leds, at currents up to 100 ma per string. the A6264 is specifically designed for use in stop/tail applica- tions where the led current is switched between a high current (indicating stop or brake) and a lower current (for normal tail light operation). current regulation is maintained and the leds protected during a short to ground at any point in the led string. a short to ground on any regulator output terminal will disable that output and set the fault flag. an open load on any output will set the fault flag and disable all outputs. remaining outputs can be re-enabled by pulling the fault flag output low. individual outputs can be disabled by connecting the output to vin. integrated thermal management reduces the regulated current level at high internal junction temperatures to limit power dis- sipation. pin functions vin supply to the control circuit and current regulators. a small value ceramic bypass capacitor, typically 100 nf, should be con- nected from close to this pin to the gnd pin. gnd ground reference connection. should be connected directly to the negative supply. full logic input to enable high led current output. open or low sets led current to the base current level. high sets led current to the sum of the base current level, and the additional high current (see detailed description of regulator operation section) . typically connected through a resistor to the stop switch input. iref 1.2 v base current reference. used for base (low) level current output, i ref . connect resistor, r ref , to gnd to set this reference current. irefh 1.2 v additional high current reference. summed with i ref for full current output. connect resistor, r refh , to gnd to set this reference current. la[1:4] current source connected to the anode of the first led in each string. connect directly to vin to disable the respective out- put. in this document ?lax? indicates any one of the four outputs. ff open drain fault flag, used with an external pull-up resistor, to indicate open, short, or overtemperature conditions. ff is inac- tive when a fault is present. during an open load condition, ff can be pulled low to force the remaining outputs on. led current level the led current is controlled by four matching linear current regulators between the vin pin and each of the lax outputs. the basic equations that determine the nominal output current at each lax pin are: given full = low, i lax = r ref 15 and, given full = high, i lax =+ r ref 15 r refh 15 (1) where i lax is in ma, and r ref and r refh are in k . in both cases, the output current may be reduced from the set level by the thermal monitor circuit. conversely the reference resistors may be calculated from: i lax(lo) = r ref 15 and i lax(hi) ? i lax(lo) = r refh 15 (2) where i lax(lo) is the required source current when full is low and i lax(hi) is the current when full is high. i lax(x) are in ma, and r ref and r refh are in k . www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 6 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com for example, where the required high-level current (full = high) is 90 ma and the required low-level current (full = low) is 20 ma, the resistor values will be: 20 == r ref 750 15 and (90 ? 20) = = r refh 214 15 these equations completely define the output currents with respect to the setting resistors. however, for further reference, see detailed description of regulator operation section. it is important to note that because the A6264 is a linear regu- lator, the maximum regulated current is limited by the power dissipation and the thermal management in the application. all current calculations assume adequate heatsinking for the dissi- pated power. thermal management is at least as important as the electrical design in all applications. in high current high ambient temperature applications the thermal management is the most important aspect of the systems design. the application section below provides further detail on thermal management and the associated limitations. operation with fewer led strings or higher currents the A6264 may be configured to use fewer than four led strings, either by connecting outputs together for higher cur- rents, or by connecting the output directly to vin to disable the regulator for that output. when a regulator is disabled, it will not indicate an open load and will not affect the fault flag or the operation of the remaining regulator outputs. safety features the circuit includes several features to ensure safe operation and to protect the leds and the A6264: ? the current regulators between vin and each lax output pro- vide a natural current limit due to the regulation. ? each lax output includes a short-to-ground detector that will disable the output to limit the dissipation. ? an open circuit on any output will disable all outputs. ? the thermal monitor reduces the regulated current as the tem- perature rises. ? thermal shutdown completely disables the outputs under ex- treme overtemperature conditions. short circuit detection a short to ground on any led cathode (figure 1a) will not result in a short fault condition. the current through the remaining leds will remain in regulation and the leds will be protected. due to the difference in the voltage drop across the leds, as a result of the short, the current match- ing in the A6264 may exceed the specified limits. any lax output that is pulled below the short detect voltage (figure 1b) will disable the regulator on that output and allow the fault flag, ff, to go high. a small current will be sourced from the disabled output to monitor the short and detect when it is removed. when the voltage at lax rises above the short detect voltage the fault flag will be removed and the regulator re-enabled. a shorted led (figure 1c) will not result in a short fault condi- tion. the current through the remaining leds will remain in regulation and the leds will be protected. due to the difference a. any led cathode short to ground. current remains regulated in non-shorted leds. matching may be affected. ff is low. b. any lax output short to ground. shorted output is disabled. other outputs remain active. ff is high. c. current remains regulated. matching may be affected. only the shorted led is inactive. ff is low. d. short between leds in different strings. current remains regulated. current is summed and shared by affected strings. intensity match dependent on voltage binning. ff is low. figure 1. short circuit conditions. A6264 la1 vin gnd la2 la3 la4 A6264 la1 vin gnd la2 la3 la4 A6264 la1 vin gnd la2 la3 la4 A6264 la1 vin gnd la2 la3 la4 www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 7 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com in the voltage drop across the leds, as a result of the short, the current matching in the A6264 may exceed the specified limits. a short between leds in different strings (figure 1d) will not result in a short fault condition. the current through the remain- ing leds will remain in regulation and the leds will be pro- tected. the current will be summed and shared by the affected strings. current matching in the strings will then depend on the led forward voltage differences. open load detection an open load condition is detected when the voltage across the regulator, v in ? v lax , is less than the open load detect voltage, v ocd , but greater than the output disable threshold voltage, v odis . when this condition is present for more than the open load detect time, t ocd , then all regulators will be disabled and the fault flag allowed to go high. the regulators will remain disabled until either the power is cycled off and on, or the fault flag, ff, is pulled low. if the power is cycled, the regulators will start in the enabled state, unless disabled by tying the output to vin, and the open load detection timer will be reset. if the open load is still present the regulators will again be disabled after the open load detect time. pulling the fault flag low will override the open load fault action and all enabled regulators will be switched on. this state will be maintained while the fault flag is held low. if the fault flag is allowed to go high the A6264 will return to the open load fault condition and will disable all regulators. each of the four regulators includes a limiter to ensure that the output voltage will not rise higher than the output disable threshold voltage below vin when driven by the regulator. this means that the voltage across the regulator will not be less than the output disable voltage, unless it is forced by connecting the lax pin to vin. however if a load becomes disconnected, the regulator will pull the lax pin up to the limit, which will ensure that the voltage across the regulator, v in ? v lax , is less than the open load detect voltage, v ocd . note that an open load may also be detected if the sum of the for- ward voltages of the leds in a string is close to or greater than the supply voltage on vin. temperature monitor a temperature monitor function, included in the A6264, reduces the led current as the silicon junction temperature of the A6264 increases (see figure 2). by mounting the A6264 on the same thermal substrate as the leds, this feature can also be used to limit the dissipation of the leds. as the junction temperature of the A6264 increases, the regulated current level is reduced, reducing the dissipated power in the A6264 and in the leds. the current is reduced from the 100% level at typically 4% per degree celsius until the point at which the current drops to 25% of the full value, defined at t jl . above this temperature the current will continue to reduce at a lower rate until the temperature reaches the overtemperature shutdown threshold temperature, t jf . the temperature at which this effect begins is defined as the thermal monitor activation temperature, t jm , and is specified, in the characteristics table, at the 90% cur- rent level. in extreme cases, if the chip temperature exceeds the overtem- perature limit, t jf , all regulators will be disabled. the tempera- ture will continue to be monitored and the regulators re-activated when the temperature drops below the threshold provided by the specified hysteresis. note that it is possible for the A6264 to transition rapidly between thermal shutdown and normal operation. this can hap- pen if the thermal mass attached to the exposed thermal pad is small and t jm is increased to close to the shutdown temperature. the period of oscillation will depend on t jm , the dissipated power, the thermal mass of any heatsink present, and the ambient temperature. 100 80 60 40 20 0 t jm t jl t jf 90 25 70 90 110 junction temperature, t j (c) relative sense current (%) 130 150 170 figure 2. temperature monitor current reduction. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 8 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com detailed description of regulator operation the current sourced from each lax output is determined by the internal reference current as: i lax = g h i refi (3) where i lax is the current sourced from each lax pin, g h is the current gain, typically 12.5, and i refi is the internal current refer- ence. the internal current reference, i refi , has two possible values depending on the state of the full input: ? when full is low, i refi is defined by i ref , the current drawn from the iref pin. ? when full is high, i refi is defined by the sum of i ref and i refh , the current drawn from the irefh pin. two external resistors determine i ref and i refh : ? resistor r ref , from iref to gnd, such that i ref = 1200 / r ref (4) ? resistor r refh , from irefh to gnd, such that i refh = 1200 / r refh (5) where i refx are in ma and r refx are in . the voltage at the iref and irefh pins is a fixed, 1.2 v refer- ence. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 9 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com application information power dissipation the most critical design considerations when using a linear regu- lator such as the A6264 are the power produced internally as heat and the rate at which that heat can be dissipated. there are three sources of power dissipation in the A6264: ? the quiescent power to run the control circuits ? the power in the reference circuit ? the power due to the regulator voltage drop the elements relating to these dissipation sources are illustrated in figure 3. quiescent power the quiescent power is the product of the quiescent current, i inq , and the supply voltage, v in , and is not related to the regulated current. the quiescent power, p q , is there- fore defined as: p q = v in i inq (6) reference power the reference circuit draws the reference current from the supply and passes it through the reference resis- tor to ground. the reference current is 8% of the output current on any one active output. when full is high, the reference circuit power is the product of the reference current and the dif- ference between the supply voltage and the reference voltage, typically 1.2 v. the reference power, p ref , is therefore defined as: p ref = r refh ( v in ? v ref ) v ref r ref v ref + ? ? ? ? ? ? ? ? (7) regulator power in most application circuits the largest dis- sipation will be produced by the output current regulators. the power dissipated in each current regulator is simply the product of the output current and the voltage drop across the regulator. the total current regulator dissipation is the sum of the dissipa- tion in each output regulator. the regulator power for each output is defined as: p regx = ( v in ? v ledx ) i ledx (8) where x is 1, 2, 3, or 4. note that the voltage drop across the regulator, v reg , is always greater than the specified minimum drop-out voltage, v do . the output current is regulated by making this voltage large enough to provide the voltage drop from the supply voltage to the total forward voltage of all leds in series, v led . the total power dissipated in the A6264 is the sum of the qui- escent power, the reference power, and the power in each of the four regulators: p dis = p q + p ref + p rega + p regb + p regc + p regd (9) the power that is dissipated in each string of leds is: p ledx = v ledx i ledx (10) where x is a, b, c, or d, and v ledx is the voltage across all leds in the string. A6264 lax i lax i inq i ref vin gnd iref r ref v ref v led v reg v in figure 3. internal power dissipation sources. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 10 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com from these equations (and as illustrated in figure 4) it can be seen that, if the power in the A6264 is not limited, then it will increase as the supply voltage increases but the power in the leds will remain constant. dissipation limits there are two features limiting the power that can be dissipated by the A6264: thermal shutdown and thermal foldback. thermal shutdown if the thermal resistance from the A6264 to the ambient temperature is high, then the silicon temperature will rise to the thermal shutdown threshold and the current will be disabled. after the current is disabled the power dissipated will drop and the temperature will fall. when the temperature falls by the hysteresis of the thermal shutdown circuit, then the current will be re-enabled and the temperature will start to rise again. this cycle will repeat continuously until the ambient temperature drops or the A6264 is switched off. the period of this thermal shutdown cycle will depend on several electrical, mechanical, and thermal parameters, and could be from a few milliseconds to a few seconds. thermal foldback if there is a good thermal connection to the A6264, then the thermal foldback feature will have time to act. this will limit the silicon temperature by reducing the regulated current and therefore the dissipation. the thermal monitor will reduce the led current as the tempera- ture of the A6264 increases above the thermal monitor activation temperature, t jm , as shown in figure 5. the figure shows the operation of the A6264 with 4 strings of 3 red leds, each string running at 50 ma. the forward voltage of each led is 2.3 v and the graph shows the current as the supply voltage increases from 14 to 17 v. as the supply voltage increases, without the thermal foldback feature, the current would remain at 50 ma, as shown by the dashed line. the solid line shows the resulting current decrease as the thermal foldback feature acts. if the thermal foldback feature did not affect led current, the current would increase the power dissipation and therefore the silicon temperature. the thermal foldback feature reduces power in the A6264 in order to limit the temperature increase, as shown in figure 6. the figure shows the operation of the A6264 under the same conditions as figure 5. that is, 4 strings of 3 red leds, each string running at 50 ma with each led forward voltage at 2.3 v. the graph shows the temperature as the supply voltage figure 4. power dissipation versus supply voltage. 3.0 2.5 2.0 1.5 1.0 0.5 0 A6264 power 70 80 90 110 100 supply voltage, v in (v) power dissipation, p d (w) 130 120 150 140 led power 4 strings v led = 6.9 v i led = 50 ma figure 5. led current versus supply voltage. figure 6. junction temperature versus supply voltage. 54 52 50 48 46 44 42 40 without thermal monitor with thermal monitor 14.0 14.5 15.0 16.0 17.0 15.5 supply voltage, v in (v) i led (ma) 16.5 4 strings v led = 6.9 v i led = 50 ma t a = 50c 130 125 120 115 110 105 100 without thermal monitor with thermal monitor 14.0 14.5 15.0 16.0 17.0 15.5 supply voltage, v in (v) t j (c) 16.5 4 strings v led = 6.9 v i led = 50 ma t a = 50c www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 11 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com increases from 14 to 17 v. without the thermal foldback feature the temperature would continue to increase up to the thermal shutdown temperature as shown by the dashed line. the solid line shows the effect of the thermal foldback function in limiting the temperature rise. figures 5 and 6 show the thermal effects where the thermal resis- tance from the silicon to the ambient temperature is 40c/w as described below. thermal dissipation the amount of heat that can pass from the silicon of the A6264 to the surrounding ambient environment depends on the thermal resistance of the structures connected to the A6264. the thermal resistance, r ja , is a measure of the temperature rise created by power dissipation and is usually measured in degrees celsius per watt (c/w). the temperature rise, t, is calculated from the power dissipated, p d , and the thermal resistance, r ja , as: t = p d r ja (11) a thermal resistance from silicon to ambient, r ja , of approxi- mately 40c/w can be achieved by mounting the A6264 on a standard fr4 double-sided printed circuit board (pcb) with a copper area of a few square inches on each side of the board under the A6264. multiple thermal vias, as shown in figure 7, help to conduct the heat from the exposed pad of the A6264 to the copper on each side of the board. the thermal resistance can be reduced by using a metal substrate or by adding a heatsink. supply voltage limits in many applications, especially in automotive systems, the avail- able supply voltage can vary over a two-to-one range, or greater when double battery or load dump conditions are taken into con- sideration. in such systems is it necessary to design the applica- tion circuit such that the system meets the required performance targets over a specified voltage range. to determine this range when using the A6264 there are two limiting conditions: ? for maximum supply voltage the limiting factor is the power that can be dissipated from the regulator without exceeding the temperature at which the thermal foldback starts to reduce the output current below an acceptable level. ? for minimum supply voltage the limiting factor is the maximum drop-out voltage of the regulator, where the difference between the load voltage and the supply is insufficient for the regulator to maintain control over the output current. minimum supply limit: regulator saturation voltage the supply voltage, v in , is always the sum of the voltage drop across the high-side regulator, v reg , and the forward voltage of the leds in the string, v led , as shown in figure 3. v led is constant for a given current and does not vary with supply voltage. therefore v reg provides the variable difference between v led and v in . v reg has a minimum value below which the regulator can no longer be guaranteed to maintain the output current within the specified accuracy. this level is defined as the regulator drop-out voltage, v do . the minimum supply voltage, below which the led current does not meet the specified accuracy, is therefore determined by the sum of the minimum drop-out voltage, v do , and the forward voltage of the leds in the string, v led . the supply voltage must figure 7. board via layout for thermal dissipation: (top) lp package (bottom) ly package. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 12 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com always be greater than this value and the minimum specified sup- ply voltage, that is: v in > v do + v led , and v in > v in (min) (12) as an example, consider the configuration used in figures 5 and 6 above, namely 4 strings of 3 red leds, each string running at 50 ma, with each led forward voltage at 2.3 v. the minimum supply voltage will be approximately: v in (min) = 0.55 + (3 2.3) = 7.45 v maximum supply limit: thermal limitation as described above, when the thermal monitor reaches the activation tempera- ture, t jm (due to increased power dissipation as the supply volt- age rises), the thermal foldback feature causes the output current to decrease. the maximum supply voltage is therefore defined as the voltage above which the led current drops below the accept- able minimum. this can be estimated by determining the maximum power that can be dissipated before the internal (junction) temperature of the A6264 reaches t jm . the maximum power dissipation is therefore defined as: p d (max) = r ja ? t (max) (13) where t(max) is difference between the thermal monitor activa- tion temperature, t jm , of the A6264 and the maximum ambient temperature, t a (max), and r ja is the thermal resistance from the internal junctions in the silicon to the ambient environment. if minimum led current is not a critical factor, then the maxi- mum voltage is simply the absolute maximum specified in the parameter tables above. application examples figure 8 shows a typical configuration for driving tail and stop light leds. although the functional features of the A6264 are specifically designed for use with automotive tail and stop lights, the ic can be used in many other general lighting applications. ? figure 9 shows the A6264 driving leds in a low voltage incan- descent lamp replacement. in such replacement applications the supply may be provided by a pwm-driven, high-side switch. the A6264 can be used in this application by applying the pwm supply directly to vin. when power is applied there will be a short startup delay, t on , before the current starts to rise. the current rise time will be limited by the internal current slew rate control. in this example the A6264 is operating with full high and with a fault output. ? figure 10 shows a typical configuration for a higher voltage supply. ? if neither fault action nor fault reporting is required, then ff may be tied to ground as in figure 11. this shows two A6264 ics driving a single string of two hb leds. ? figure 12 shows on combination of outputs tied together. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 13 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com A6264 + la1 vin gnd la2 la3 la4 full ff irefh iref A6264 la1 vin gnd la2 la3 la4 full ff irefh iref A6264 + vin gnd full ff irefh iref la1 la2 la3 la4 A6264 vin gnd full irefh iref la1 la2 la3 la4 A6264 + vin fused or pwm 12 v supply fused or pwm 12 v supply gnd full ff irefh iref ff A6264 vin gnd ff irefh iref + automotive 12 v power net automotive 12 v power net stop switch tail switch stop switch stop switch tail switch + automotive 24 v power net high-side pwm source full la1 la2 la3 la4 la1 la2 la3 la4 figure 8. common tail / stop lamp configuration. figure 9. incandescent lamp replacement. figure 12. led outputs options. figure 10. higher voltage supply application. figure 11. disabling ff, driving high brightness (hb) leds with two A6264s. www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 14 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com package lp, 16-pin tssop with exposed thermal pad a 1.20 max 0.15 0.00 0.30 0.19 0.20 0.09 8o 0o 0.60 0.15 1.00 ref c seating plane c 0.10 16x 0.65 bsc 0.25 bsc 2 1 16 5.000.10 4.400.10 6.400.20 gauge plane seating plane a terminal #1 mark area b for reference only; not for tooling use (reference mo-153 abt) dimensions in millimeters dimensions exclusive of mold flash, gate burrs, and dambar protrusions exact case and lead configuration at supplier discretion within limits shown b c exposed thermal pad (bottom surface); dimensions may vary with device 6.10 0.65 0.45 1.70 3.00 3.00 16 2 1 reference land pattern layout (reference ipc7351 sop65p640x110-17m); all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and pcb layout tolerances; when mounting on a multilayer pcb, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference eia/jedec standard jesd51-5) pcb layout reference view c branded face 30.05 30.05 www.datasheet.co.kr datasheet pdf - http://www..net/
automotive stop/tail led array driver A6264 15 allegro microsystems, inc. 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com package ly, 10-pin msop with exposed thermal pad for the latest version of this document, visit our website: www.allegromicro.com terminal #1 mark area a gauge plane seating plane 0.86 0.05 seating plane 0.50 ref 0.25 2 1 10 2 1 10 a b 0.53 0.10 0.15 0.05 0.05 0.15 0 to 6 3.00 0.10 3.00 0.10 4.88 0.20 1.98 1.73 0.27 0.18 for reference only; not for tooling use (reference jedec mo-187) dimensions in millimeters dimensions exclusive of mold flash, gate burrs, and dambar protrusions exact case and lead configuration at supplier discretion within limits shown b exposed thermal pad (bottom surface) copyright ?2009-2010, allegro microsystems, inc. the products described here are manufactured under one or more u.s. patents or u.s. patents pending. allegro microsystems, inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per- mit improvements in the per for mance, reliability, or manufacturability of its products. before placing an order, the user is cautioned to verify that the information being relied upon is current. allegro?s products are not to be used in life support devices or systems, if a failure of an allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. the in for ma tion in clud ed herein is believed to be ac cu rate and reliable. how ev er, allegro microsystems, inc. assumes no re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which may result from its use. www.datasheet.co.kr datasheet pdf - http://www..net/

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