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AL8400/ AL8400q document number: ds35115 rev. 4 - 2 1 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q linear led driver-controller with 200mv current sense voltage and automotive grade description the AL8400 is a 5-terminal adjust able linear led driver-controller offering excellent temperature stability and output handling capability. the AL8400 simplifies the design of linear and isolated led drivers. with its low 200mv current sense fb pin, it controls the regulation of led current with minimal power dissipation when compared to traditional linear led drivers. this makes it ideal for medium to high current led driving. the AL8400 open-collector output can operate from 0.2v to 18v enabling it to drive external mosfet and bipolar transistors. this enables the mosfet and bipolar selection to be optimized for the chosen application. it also provides the capability to drive longer led chains, by tapping v cc from the chain, where the chain voltage may exceed 18v. it is available in the space saving low profile sot353 package. the AL8400q is automotive grade and is aec-q100 grade 1 qualified. applications ? isolated offline led lamps ? linear led driver ? led signs ? instrumentation illumination pin assignments features ? low reference voltage (v fb = 0.2v) ? -40 to +125c temperature range ? 3% reference voltage tolerance at +25c ? low temperature drift ? 0.2v to 18v open-collector output ? high power supply rejection: ? (> 45db at 300khz) ? AL8400qse-7 automotive grade qualified to aec-q100 grade 1 ? sot353: available in ?green? molding compound (no br, sb) ? lead-free finish; rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) ? notes: 1. eu directive 2002/95/ec (rohs) & 2011/65/eu (roh s 2) compliant. all applicable rohs exemptions applied. 2. see http://www.diodes.com for more in formation about diodes incorpor ated?s definitions of halogen- and antimony-free, "gree n" and lead-free. 3. halogen- and antimony-free "green? products are defined as those which contain <900ppm br omine, <900ppm chlorine (<1500ppm t otal br + cl) and <1000ppm antimony compounds. typical applications circuit out fb e1 gnd r b q2 r set c l i led = v ref /r set c d AL8400 vcc 1 2 3 5 4 gnd vcc ? green
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 2 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q pin descriptions pin number name function 1 e1 emitter connection. connect to gnd. 2 gnd analog ground. ground return for reference and amplifier. connect to e1. 3 v cc supply input. connect a 0.47 f ceramic capacitor close to the device from v cc to gnd. 4 fb feedback input. regulates to 200mv nominal. 5 out output. connect a capacitor close to device between out and gnd. see the applications information section. functional block diagram figure 1 block diagram absolute maximum ratings (@t a = +25c, unless otherwise specified.) symbol parameter rating unit v cc supply voltage relative to gnd 20 v v out out voltage relative to gnd 20 v v fb fb voltage relative to gnd 20 v v e1 e1 voltage relative to gnd -0.3 to+0.3 v t j operating junction temperature -40 to 150 c t st storage temperature -55 to 150 c these are stress ratings only. operation outside the absolute maximum ratings may cause device failure. operation at the absolute maximum rating for extended periods may reduce device reliability. package thermal data package ja p dis t a = +25c, t j = +150c sot353 400c/w 310mw
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 3 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q recommended operating conditions (@t a = +25c, unless otherwise specified.) symbol parameter min max units v cc supply voltage range 2.2 18 v v out out voltage range 0.2 18 i out out pin current 0.3 15 ma t a operating ambient temperature range -40 +125 c electrical characteristics (note 4) (@t a = +25c, v cc = 12v, v out = v fb , i out = 1ma, unless otherwise specified.) symbol parameter conditions min typ max units v fb feedback voltage t a = +25c 0.194 0.2 0.206 v t a = -40c to +125c 0.190 0.210 fb load feedback pin load regulation i out = 1 to 15ma t a = +25c 3.1 6 mv t a = -40c to +125c 10 fb line feedback pin line regulation v cc = 2.2v to 18v t a = +25c 0.1 1.5 mv t a = -40c to +125c 2 fb ovr output voltage regulation v out = 0.2v to 18v, i out =1ma (ref. figure 1) t a = +25c 2 mv t a = -40c to +125c 3 i fb fb input bias current v cc = 18v t a = +25c -45 na t a = -40c to +125c -200 0 i cc supply current v cc = 2.2v to 18v, i out =10ma t a = +25c 0.48 1 ma t a = -40c to +125c 1.5 i out(lk) out leakage current v cc = 18v, v out = 18v, v fb =0v t a = +25c 0.1 a t a = +125c 1 z out dynamic output impedance i out = 1 to 15ma, f < 1khz t a = +25c 0.25 0.4 t a = -40c to +125c 0.6 psrr power supply rejection ratio f = 300khz, v a c = 0.3v pp t a = +25c 45 db bw amplifier unity gain frequency t a = +25c 600 khz g amplifier transconductance t a = +25c 4500 ma/v note: 4. production testing of the device is performed at +25c. functional operatio n of the device and parameters specified ov er the operating temperature range are guaranteed by design, characterization and process control. typical characteristics load regulation line regulation
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 4 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q typical characteristics (cont.) supply current with input voltage supply current with load current fb voltage change with temperature fb input current with temperature mosfet driving bipolar transistor driving
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 5 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information description the AL8400 linear led driver controller uses an external pass element to drive the leds and uses its fb pin to sense the led cu rrent through an external resistor r set . the pass element is driven by the AL8400?s open collecto r out pin which allows the pass element to be either an npn transistor or n-channel mosfet. an external pull-up resistor, r b , is required to be connected from the out pin to v cc . this resistor supplies the output bias current of the AL8400 together with any current which the pass element requires. in order to maintain the accuracy of the 200mv reference voltage on the fb pin the value of r b should be set so that the out pin sinks 1ma. stability as with all ics, for best stability a 0.1f minimum (x7r ceramic) power supply decoupling capacitor, c d , connected between v cc and ground (see figure 2) is recommended. c d should be placed as close to the v cc pin as possible < 5mm. figure 2 application circuit using bipolar transistor the AL8400 requires an output capacitor, c l in figure 2, to be connected from the out pin to ground. this capacitor is required to compensate the current control loop of the AL8400. this compensation capacitor must be placed as close to the out pin as possible < 5mm. if the pcb traces are too long, there is the possibility of oscillation at about 5mhz. the capacitors c d and c l must be mounted immediately adjacent to the AL8400, with direct connections to out, e1, gnd and v cc . the limit of 5mm provides a good margin for stability. the value of capacitor c l is determined from the value of the pull-up resistor r b so that: c l x r b 2ms for example if r b = 1k , then c l must be 2f or greater. the recommended capacitor type is x7r ceramic. -50 0 50 100 150 200 1 10 100 1k 10k 100k 1m frequency (hz) ga in (db) 0 45 90 135 180 225 phase (deg) gain phase v out = 0.6v c out = 2 .2uf -50 0 50 100 150 200 1 10 100 1k 10k 100k 1m frequency (hz) ga in (db) 0 45 90 135 180 225 phase (deg) gain phase gain phase v out = 0.6v c out = 2 .2uf figure 3 gain and phase vs. frequency with r b = 1k ? and c l = 2.2f v out = 0.6v r b = 1k ? c l = 2.2f
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 6 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information (cont.) bipolar transistor as the pass element for driving currents in the region of about 50ma to about 400ma, t he recommended npn is dnls320e in the sot223 package. the hi gh dc current gain of the dnls320e is useful in this app lication, in order to minimize the current in r b . the design procedure is as follows, referring to figure 4. figure 4 application circuit using bipolar transistor there are two important equations for the circuit: led circuit path: 1. v cc = (v led + v ce + v fb ) where v fb is approximately the internal reference voltage of 200mv. the maximum total led voltage plus the reference voltage determi nes the minimum supply voltage. substituting into equation 1 yi elds: fb cesat maxled mincc vv v v ++ = where v ledmax is the maximum led chain voltage. control drive circuit path 2. v cc = (v rb + v be + v fb ) for a bipolar transistor the voltage (v rb ) across bias resistor r b consists of the base current of q2 and the output current of the AL8400. so rearranging equation 2 yields the boundaries for allowable r b values: 3. maxbminout fb maxbe mincc maxb ii v vv r + ?? = where i bmax is the maximum transistor base current minfe led maxb h i i = where h femin is the minimum dc current gain of the transistor. 4. minbmaxout fb minbe maxcc minb ii vv v r + ?? = where i bmin is the minimum transistor base current maxfe led minb h i i = where h femax is the maximum dc current gain of the transistor. the value of r b should be set somewhere between r bmax and r bmin with the target of trying to get i out of the AL8400 close to 1ma for nominal conditions. once r b has been determined the value for compensation capacitor, c l , should be calculated. b l r ms2 c finally, the bipolar selection is also in fluenced by the maximum power dissipation p tot = i led x (v cc ? v led ? v ref ) = i led x v ce since this determines the package choice ( ja ) in order to keep the junction temperat ure below the maximum value allowed. t j = t a + p tot x ja where t j(max) is the maximum operating junction temperature, t a is the ambient temperature, ja is the junction to ambient thermal resistance.
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 7 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information (cont.) bipolar example ? choosing r b and c l the driver is required to control 3 series connected leds at 150ma 10% from a 12v 5% supply. each led has a forward voltage o f 3v minimum and of 3.6v maximum. from this information the minimum supply voltage is 11.4v and the maximum led chain voltage is 10.8v. rearranging equation 1 ( page 7); the minimum voltage drop across the bipolar transistor is determined to be: v4.0v2.0v8.10v4.11v vvv fb maxled mincc ce =??=? ?= we will use the dnls320e bipolar transistor (q2.) r bmax the dnls320e datasheet table states: v ce(sat)max = 0.1v at i c = 100ma, i b = 0.5ma h femin = 500 @ i c = 100ma, v ce = 2v; the datasheet graph (see left) shows a very slow variation at 100ma, so a value of 500 is considered appropriate. then 500 ma150 i maxb = = 0.3ma the minimum recommended i out for AL8400 is 0.3ma and the maximum v be , according to the dnls320e datasheet graph (figure 6), is approximately 0.8v at -55c. from these and equation 3, the maximu m allowed bias resistor value is: = + ?? = maxbminout fb maxbe mincc maxb ii v vv r 0003.00003.0 2.08.04.11 + ?? = = 17.3k ? figure 5 dnls320e h fe vs. i c figure 6 dnls320e v be vs. i c
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 8 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information (cont.) bipolar example ? choosing r b and c l (cont.) r bmin to ensure that the output capability of t he AL8400 is not exceeded at maximum v in , maximum h fe and minimum v be , these values should be substituted back into the r b equation to determine the minimum allowable value for r b . h femax is about 1200 @ i c = 100ma, and a temperature of +85c (figure 5) which results in: 1200 150 i minb = = 0.125ma the maximum recommended i out for AL8400 is 15ma.the minimum v be , according to the dnls320e datasheet graph (figure 6), is approximately 0.4v at 85c and assuming v ccmax = 12.6v, then from equation 4 the bias resistor value is: minbmaxout fb minbe maxcc minb ii vv v r + ?? = = 000125.0015.0 2.04.04.8 + ?? = = 516 ? this is less than 17k ? and so the AL8400 output current is within its ratings. c l choosing r b = 11k ? satisfies the requirements for the AL8400 conformance and sets approximately 1ma in the out pin. the required compensation capacitor can t herefore be calculated from: f18.0 k11 ms2 c l ? ? 180nf the value of r set is v ref /i led so: r set = 0.2/0.15 = 1.333 ? ? choosing two 2.7 ? yields 1.35 ? giving an approximate 1.3% difference from target. finally, the maximum power dissipation of the external bipolar transistor is: p tot = i led x v cemax = i led x (v cc_max ? v led_min ? v fb ) = 0.51w this determines the package choice ( ja ) in order to keep the junction temperature of the bipol ar transistor below the maximum value allowed. at a maximum ambient temperature of +60c the junction temperature becomes t j = t a + p tot x ja = 60 + 0.51 x 125 = +123.75c n-channel mosfet as the pass element alternatively, an n-channel mosfet may be used in the same configuration. the current in r b is then reduced compared to the case in which the bipolar transistor is used. for led currents up to about 400m a a suitable mosfet is dmn6068se in the sot223 package. the d esign procedure is as follows, referring to figure 7. figure 7 application circuit using mosfet
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 9 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information (cont.) n-channel mosfet as the pass element (cont.) the equations (1 and 2) for the bipol ar transistor are transformed into: led circuit path: 5. v cc = (v led + v ds + v fb ) where vfb is approximately the internal reference voltage of 200mv. control drive circuit path 6. v cc = (v rb + v gs + v fb ) the maximum total led voltage plus the reference voltage determi nes the minimum supply voltage. substituting into equation 5 yi elds: fb dsmin led mincc vvv v ++= the mosfet dc gate current is negligible, so the bias resistor r b has only to provide the minimum output current of the AL8400. so rearranging equation 6 yields the boundaries for allowable r b values: 7. maxout fb mings maxcc minb i vv v r ?? = 8. minout fb maxgs mincc maxb i v vv r ? ? = where i outmax is the AL8400 maximum output current where i outmin is the AL8400 minimum output current once the value of r b has been determined, somewhere between r bmax and r bmin ? trying to get i out close to 1ma for all variations, the value for compensation capacitor, c l , should be calculated. the mosfet selection is also infl uenced by the maximum power dissipation p tot = i led * (v cc ? v led ? v fb ) = i led * v ds since this determines the package choice ( ja ) in order to keep the junction temperat ure below the maximum value allowed. t j = t a + p tot ? ja where t j(max) is the maximum operating junction temperature, t a is the ambient temperature, ja is the junction to ambient thermal resistance. low supply voltages and mosfet as pass element when driving a single led at low supply volt ages, a low threshold mosfet or high gai n npn bipolar transis tor should be used as the led driving pass transistor. this is because a standard threshold voltage mosfet might not have enough gate-source voltage to ensure that it is sufficiently enhanced to regulate the led current. mosfet example choosing r b and c l the driver is required to control 3 series connected leds at 200ma 10% from an 12v 5% supply. each led has a forward voltage of 3v minimum and of 3.6v maximum. therefore the minimum supply voltage is 11.4v and the maximum led chain voltage is 10.8v. rearranging equation 5 (page 9); the minimum voltage drop across the mosfet is required to be: =? ?= fb maxled mincc ds led v vvri v2.0v8.10v4.11 ? ? = = 0.4v ? r ds(on) 2? we will use the dmn6068se n-channel mosfet (q2) with a maximum r ds(on) of 100m ? at v gs = 4.5v.
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 10 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information (cont.) mosfet example choosing r b and c l (cont.) r bmax the minimum recommended i out for AL8400 is 0.3ma. the maximum v gs is not stated explicitly, but from the datasheet graphs (figures 8 and 9) it is expected to be approximately 3.8v at -50c. = ? ? = minout fb maxgs mincc maxb i v vv r = ?? = ma3.0 v2.0v8.3v4.11 24.7k ? to ensure that the output capability of the AL8400 is not exceeded at maximum v in and minimum v gs these values should be substituted back into the r b equation to determine the minimum allowable value for r b . r bmin the maximum recommended i out for the AL8400 is 15ma. the minimum v gs is about 1v and assuming v ccmax = 8.4v: maxout fb mings maxcc minb i vv v r ?? = = = ma15 v2.0v1v6.12 ?? = 480 ? this is less than 12k ? and so the AL8400 output current is within its ratings. figure 8 typical transfer characteristics figure 9 normalised curves and temperature assuming v gs ~ 3v and choosing an r b = 8.2k ? satisfies the requirements for the AL8400 conformance and sets approximately 1ma in the out pin. the required compensation capacit or can therefore be calculated from: f243.0 k2.8 ms2 c l ? ? 220nf the value of r set is v ref /i led r set = 0.2/0.2 = 1 ? finally, the maximum power dissipation of the external mosfet is: p tot = i led x v dsmax = i led x (v ccmax ? v ledmin ? v fb ) = 0.2 x( 12.6 ? 9 -0.2) = 0.68w this determines the package choice ( ja ) in order to keep the junction temperature below the maximum value allowed. t j = t a + p tot x ja = 60 + 0.68 x 62.5 = +102.5? c
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 11 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q application information (cont.) high voltage operation the AL8400 also provides the capability to dr ive longer led chains as t he voltage across the led chain is determined by the ext ernal switch. the lower supply voltage for the AL8400 can be derived from the suppl y to the led chain either by putting a series resistor to the AL8400?s v cc pin and putting a suitable zener diode from its v cc to gnd figure 10 or by tapping its v cc from the led chain figure 11. figure 10 high voltage operation with zener diode from vin equations 1 and 2 (from page 7) now transform into: led circuit path: 1. v in = (v led + v ce + v fb ) control dri v e circuit path 2. v cc = (v rb + v be + v fb ) when the supply voltage for the AL8400 is derived using a zener diode, care has to be ta ken in dimensioning the resistor r1. th e current taken through r1 from v in has to be large enough to polarize the zener, bias the AL8400 supply current, AL8400 output current and the pass transistor across all input voltage variations. an alternative way of operating the AL8400 from rails greater than 18v is to take its power supply from the led chain itself. figure 11 high voltage operation tapping v cc from the led string when the supply voltage for the AL8400 is derived from the led stri ng, care has to be taken in dimensioning the resistor r b . the current spilled from the led chain can reduce the accuracy of the system and brightness matching between the led.
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 12 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q ordering information part number package code packaging 7? tape and reel automotive grade quantity part number suffix AL8400qse-7 se sot353 3000/tape & reel -7 y (note 5) AL8400se-7 se sot353 3000/tape & reel -7 - note: 5. qualified to aec-q100 grade 1. marking information (1) sot353 1 2 3 5 7 4 xx y w x ( top view ) xx : identification code w : week : a~z : 1~26 week; x : a~z : green y : year 0~9 a~z : 27~52 week; z represents 52 and 53 week part number package identification code AL8400se-7 sot353 b4 AL8400qse-7 sot353 b4 package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. sot353 dim min max a 0.10 0.30 b 1.15 1.35 c 2.00 2.20 d 0.65 typ f 0.40 0.45 h 1.80 2.20 j 0 0.10 k 0.90 1.00 l 0.25 0.40 m 0.10 0.22 0 8 all dimensions in mm a m j l d b c h k f
AL8400/ AL8400q document number: ds35115 rev. 4 - 2 13 of 13 www.diodes.com august 2012 ? diodes incorporated AL8400 / a l8400q suggested pad layout please see ap02001 at http://www.diodes.com/dat asheets/ap02001.pdf for the latest version. important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product descri bed herein. diodes incorporated does not assume any liability arising out of the application or use of this document or an y product described herein; neither does di odes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or us er of this document or products described herein in such applica tions shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes inco rporated products for any unintended or una uthorized application, customers shall i ndemnify and hold diodes incorporated and its representativ es harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death a ssociated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. life support diodes incorporated products are specifically not authorized for use as critical component s in life support devices or systems without the express written approval of the chief executive offi cer of diodes incorporated. as used herein: a. life support devices or syst ems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when proper ly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support devic e or system whose failure to perform can be reasonably expect ed to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifi cations of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-rel ated requirements concerning the ir products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or s ystems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporate d and its representatives against any damages arisi ng out of the use of diodes incorporated pr oducts in such safety-critical, life suppor t devices or systems. copyright ? 2012, diodes incorporated www.diodes.com dimensions value (in mm) z 2.5 g 1.3 x 0.42 y 0.6 c1 1.9 c2 0.65 x z y c1 c2 c2 g

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