general description the max16832a/max16832c step-down constant-cur- rent high-brightness led (hb led) drivers provide a cost-effective design solution for automotive interior/exterior lighting, architectural and ambient light- ing, led bulbs, and other led illumination applications. the max16832a/max16832c operate from a +6.5v to +65v input voltage range and can provide an output current up to 700ma, if operated up to a temperature of +125?, or up to a 1a if operated up to a temperature of +105?. a high-side current-sense resistor adjusts the output current, and a dedicated pulse-width modu- lation (pwm) input enables pulsed led dimming over a wide range of brightness levels. these devices are well suited for applications requiring a wide input voltage range. the high-side current sens- ing and an integrated current-setting circuitry minimize the number of external components while delivering an average output current with ?% accuracy. a hysteretic control method ensures excellent input supply rejection and fast response during load transients and pwm dim- ming. the max16832a allows 10% current ripple, and the max16832c allows 30% current ripple. both devices operate up to a 2mhz switching frequency, thus allowing the use of small-sized components. the max16832a/max16832c offer an analog dimming feature that reduces the output current by applying an external dc voltage below the internal 2v threshold volt- age from temp_i to gnd. temp_i also sources 25? to a negative temperature coefficient (ntc) thermistor con- nected between temp_i and gnd, thus providing an analog thermal-foldback feature that reduces the led current when the temperature of the led string exceeds a specified temperature point. additional features include thermal-shutdown protection. the max16832a/max16832c operate over the -40? to +125? automotive temperature range and are available in a thermally enhanced 8-pin so package. applications architectural, industrial, and ambient lighting automotive rcl, drl, and fog lights heads-up displays indicator and emergency lighting mr16 and mr111 led lights features high-efficiency solution 6.5v to 65v input voltage range output current up to 1a on-board 65v, 0.45 ? power mosfet hysteretic control: up to 2mhz switching frequency ?% led current accuracy 200mv current-sense reference resistor-programmable constant led current integrated high-side current sense thermal-foldback protection/linear dimming thermal-shutdown protection available in a thermally enhanced 8-pin so package -40? to +125? operating temperature range max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense ________________________________________________________________ maxim integrated products 1 ordering information lx lx pgnd 1 2 8 7 temp_i dim in gnd cs 3 4 6 5 max16832a max16832c l1 c2 on off d1 hb leds ntc * * optional r sense v in c1 typical application circuit 19-4140; rev 5; 3/12 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. part temp range pin-package max16832a asa+ -40? to +125? 8 so-ep* max16832c asa+ -40? to +125? 8 so-ep* pin configuration appears at end of data sheet.
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = +24v, v dim = v in , t a = t j = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four- layer board. for detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial . in, cs, lx, dim to gnd .........................................-0.3v to +70v temp_i to gnd .......................................................-0.3v to +6v pgnd to gnd ......................................................-0.3v to +0.3v cs to in .................................................................-0.3v to +0.3v maximum current into any pin (except in, lx, and pgnd).............................................20ma continuous power dissipation (t a = +70?) 8-pin so (derate 18.9mw/? above +70?)...........1509.4mw operating temperature range 700ma (max) output current ........................-40? to +125? 1a (max) output current ...............................-40? to +105? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? soldering (reflow).............................................................+260? lead temperature (soldering, 10s) .................................+300? pin-to-pin esd ratings......................................................?.5kv parameter symbol conditions min typ max units input voltage range v in 6.5 65 v ground current no switching 1.5 ma supply current v dim < 0.6v, v in = 12v 350 ? undervoltage lockout (uvlo) v cs = v in - 100mv, v in rising until v lx < 0.5v in 6.25 6.5 undervoltage lockout uvlo v cs = v in - 100mv, v in falling until v lx > 0.5v in 6.0 v undervoltage-lockout hysteresis 0.5 v sense comparator max16832a, v in - v cs rising from 140mv until v lx > 0.5v in , v dim = 5v 197 205 213 sense voltage threshold high v snshi max16832c, v in - v cs rising from 140mv until v lx > 0.5v in , v dim = 5v 218 230 236 mv max16832a, v in - v cs falling from 260mv until v lx < 0.5v in , v dim = 5v 185 190 198 sense voltage threshold low v snslo max16832c, v in - v cs falling from 260mv until v lx < 0.5v in , v dim = 5v 166 170 180 mv propagation delay to output high t dpdh falling edge of v in - v cs from 140mv to 260mv to v lx > 0.5v in 50 ns propagation delay to output low t dpdl rising edge of v cs - v in from 260mv to 140mv to v lx < 0.5v in 50 ns cs input current i csin v in - v cs = 200mv, v in = v cs 3.5 ? package thermal characteristics (note 1) so-ep junction-to-ambient thermal resistance ( ja )...............+53?/w junction-to-case thermal resistance ( jc )......................+5?/w
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense _______________________________________________________________________________________ 3 parameter symbol conditions min typ max units internal mosfet v in = v dim = 24v, v cs = 23.9v, i lx = 700ma 0.45 0.9 drain-to-source resistance r dson v in = v dim = 6.0v, v cs = 5.9v, i lx = 700ma 12 ? lx leakage current i lx_leak v dim = 0v, v lx = 65v 10 ? dim input dim input-voltage high v ih v in - v cs = 100mv 2.8 v dim input-voltage low v il v cs - v in = 100mv 0.6 v dim turn-on time t dim_on v dim rising edge to v lx < 0.5v in 60 ns dim input leakage high v dim = v in 815 a dim input leakage low v dim = 0v -3 -1.5 0 a thermal shutdown thermal-shutdown threshold temperature rising +165 o c thermal-shutdown threshold hysteresis 10 o c thermal foldback thermal-foldback enable threshold voltage v tfb_on v dim = 5v 1.9 2.0 2.12 v thermal-foldback slope fb slope v dim = 5v 0.75 1/v temp_i output bias current i temp_i t a = +25 o c 25 26.5 28 ? electrical characteristics (continued) (v in = +24v, v dim = v in , t a = t j = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) efficiency vs. input voltage max16832a toc01 v in (v) efficiency (%) 55 45 35 25 15 75 80 85 90 95 100 70 565 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 9 leds duty cycle vs. input voltage max16832a toc02 v in (v) duty cycle (%) 55 45 35 25 15 10 20 30 40 50 60 70 80 90 100 0 565 1 led 3 leds 5 leds 7 leds 15 leds 13 leds 11 leds frequency vs. input voltage max16832a toc03 v in (v) frequency (khz) 55 45 35 25 15 50 100 150 200 250 300 350 400 450 500 0 565 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds 16 leds typical operating characteristics (v in = v dim = 48v, r sense = 0.3 ? , l = 220? (connected between in and cs). typical values are at t a = +25?, unless otherwise noted.)
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense 4 _______________________________________________________________________________________ normalized i led current vs. input voltage max16832a toc04 v in (v) normalized i led current 60 55 50 45 40 35 30 25 20 15 10 5 065 0.96 0.97 0.98 0.99 1.00 1.01 1.02 1.03 1.04 1.05 0.95 1 led 3 leds 5 leds 7 leds 9 leds 11 leds 13 leds 15 leds quiescent current vs. input voltage max16832a toc05 v in (v) quiescent current ( a) 60 55 45 50 15 20 25 30 35 40 5 10 50 100 150 200 250 300 350 400 450 500 0 065 v dim = 0v pwm dimming at 200hz (10% duty cycle) max16832a toc06 1ms/div i led 200ma/div 0 0 v dim 5v/div v in = 48v 8 leds pwm dimming at 200hz (90% duty cycle ) max16822a toc07 1ms/div i led 200ma/div v dim 5v/div 0 0 v in = 48v 8 leds pwm dimming at 20khz (90% duty cycle) max16832a toc08 10 s/div i led 200ma/div v dim 5v/div 0 0 v in = 48v 8 leds led current vs. v temp_i max16832a toc09 v temp_i (v) led current (ma) 2.4 2.0 1.2 1.6 0.8 0.4 500 450 400 350 300 250 200 150 100 50 650 550 600 750 700 800 0 0 2.8 i led vs. temperature max16832a toc10 temperature ( c) i led (a) 110 95 80 65 50 35 20 5 -10 -25 -40 125 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 v in = 48v typical operating characteristics (continued) (v in = v dim = 48v, r sense = 0.3 ? , l = 220? (connected between in and cs). typical values are at t a = +25?, unless otherwise noted.)
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense _______________________________________________________________________________________ 5 lx rdson vs. temperature max16832a toc11 temperature ( c) lx rdson ( ? ) 110 95 80 65 50 35 20 5 -10 -25 0.2 0.3 0.4 0.5 0.6 0.7 0.1 -40 125 v in = 6.5v v in = 65v v in = 48v i temp_i vs. temperature max16832a toc12 i temp_i ( a) 25.5 26.0 26.5 27.0 27.5 28.0 28.5 29.0 29.5 30.0 25.0 temperature ( c) 110 95 80 65 50 35 20 5 -10 -25 -40 125 v in = 48v typical operating characteristics (continued) (v in = v dim = 48v, r sense = 0.3 ? , l = 220? (connected between in and cs). typical values are at t a = +25?, unless otherwise noted.) pin description pin name function 1 cs current-sense input. connect a resistor between in and cs to program the led current. 2 in positive supply voltage input. bypass with a 1? or higher value capacitor to gnd. 3 gnd ground 4 pgnd power ground 5, 6 lx switching node 7 dim logic-level dimming input. drive dim low to turn off the current regulator. drive dim high to enable the current regulator. 8 temp_i thermal foldback control and linear dimming input. bypass with a 0.01? capacitor to gnd if thermal foldback or analog dimming is used. see the thermal foldback section. ?p exposed pad. connect ep to a large-area ground plane for effective power dissipation. do not use as the ic ground connection. detailed description the max16832a/max16832c are step-down, constant- current, hb led drivers. these devices operate from a +6.5v to +65v input voltage range. the maximum output is 1a, if the part is used at temperatures up to t a = +105?, or 700ma, if it is used up to t a = +125?. a high-side current-sense resistor sets the output current and a dedicated pwm dimming input enables pulsed led dimming over a wide range of brightness levels. a high-side current-sensing scheme and an on-board current-setting circuitry minimize the number of exter- nal components while delivering led current with ?% accuracy, using a 1% sense resistor. see figure 1 for a functional diagram.
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense 6 _______________________________________________________________________________________ v cc regulator open led comparator lx in cs dim temp_i v tfb_on 2v pgnd gnd current-sense comparator pwm dimming 0.45 ? , 65v nmos switch uvlo comparator thermal foldback comparator bandgap ref dim buffer v cc _ana v cc _ana v cc _ana i set 25 a 1.23v gate driver max16832a max16832c figure 1. functional diagram
undervoltage lockout (uvlo) the max16832a/max16832c include a uvlo with 500mv hysteresis. the internal mosfet turns off when v in falls below 5.5v to 6.0v. dim input led dimming is achieved by applying a pwm signal at dim. a logic level below 0.6v at dim forces the max16832a/max16832cs?output low, thus turning off the led current. to turn the led current on, the logic level at dim must be greater than 2.8v. thermal shutdown the max16832a/max16832c thermal-shutdown feature turns off the lx driver when the junction temperature exceeds +165?. the lx driver turns back on when the junction temperature drops 10? below the shutdown temperature threshold. analog dimming the max16832a/max16832c offer an analog-dimming feature that reduces the output current when the volt- age at temp_i is below the internal 2v threshold volt- age. the max16832a/max16832c achieve analog dimming by either an external dc voltage source con- nected between temp_i and ground or by a voltage on a resistor connected across temp_i and ground induced by an internal current source of 25?. when the voltage at temp_i is below the internal 2v threshold limit, the max16832a/max16832c reduce the led cur- rent. use the following formula to set the analog dim- ming current: where v tfb_on = 2v and fb slope = 0.75 are obtained from the electrical characteristics table and v ad is the voltage at temp_i. thermal foldback the max16832a/max16832c include a thermal-fold- back feature that reduces the output current when the temperature of the led string exceeds a specified tem- perature point. these devices enter thermal-foldback mode when the voltage drop on the ntc thermistor, thermally attached to the leds and electrically con- nected between temp_i and ground, drops below the internal 2v threshold limit. applications information selecting r sense to set led current the led current is programmed with a current-sense resistor connected between in and cs. use the follow- ing equation to calculate the value of this resistor: where v snshi is the sense voltage threshold high and v snslo is the sense voltage threshold low (see the electrical characteristics table for values). current-regulator operation the max16832a/max16832c regulate the led current using a comparator with hysteresis (see figure 2). as the current through the inductor ramps up and the volt- age across the sense resistor reaches the upper threshold, the internal mosfet turns off. the internal mosfet turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resistor equals the lower threshold. use the following equation to determine the operating frequency: where n is the number of leds, v led is the forward voltage drop of 1 led, and ? v = (v snshi - v snslo ). inductor selection the max16832a/max16832c operate up to a switch- ing frequency of 2mhz. for space-sensitive applica- tions, the high switching frequency allows the size of the inductor to be reduced. use the following formula to calculate an approximate inductor value and use the closest standard value: for component selection, use the max16832a/c design tool available at: www.maxim-ic.com/max16832- software . l approx vnv nv r vvf in led led sense in sw (.) () = ? ? f vnv nv r vvl sw in led led sense in = ? () ? r vvv ia sense snshi snslo led () ()() () ?= + 1 2 iai a fb v vvv tf led slope tfb on ad () () () _ = ? ? ? ? ? ? () ? ? ? ? ? ? ?? 1 1 max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense _______________________________________________________________________________________ 7
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense 8 _______________________________________________________________________________________ freewheeling-diode selection for stability and best efficiency, a low forward-voltage drop diode with fast reverse-recovery time and low capacitance is recommended. a schottky diode is a good choice as long as its breakdown voltage is high enough to withstand the maximum operating voltage. pcb layout guidelines careful pcb layout is critical to achieve low switching losses and stable operation. in normal operation, there are two power loops. one is formed when the internal mosfet is on and the high current flows from ground through the input cap, r sense , the led load, the inductor, and the internal mosfet back to ground. the second loop is formed when the internal mosfet is off and the high current circulates from the input cap posi- tive terminal through r sense , the led load, the induc- tor, and the freewheeling diode and back to the input cap positive terminal. note that the current through r sense , the led load, and the inductor is basically dc with some triangular ripple (low noise). the high-noise, large signal, fast transition switching currents only flow through the freewheeling diode to the input cap positive terminal, or through the mosfet to ground and then to the input cap positive terminal. without a proper pcb layout, these square-wave switching currents can cre- ate problems in a hysteretic led driver. the current control depends solely on the voltage across r sense . any noise pickup on this node induces erratic switching of the internal mosfet (the ic will operate at a much higher frequency). to help prevent this, place r sense as close as possible to cs and in and keep the sense traces short. it is especially impor- tant to keep the square-wave switching currents in the freewheeling diode away from r sense . to minimize interference, place the freewheeling diode on the oppo- site side of the ic as r sense and position the input capacitor near the diode so it can return the high fre- quency currents to ground. the layout in figure 3 should be used as a guideline. the dashed line shows the path of the high frequency components that cause disruption in operation. for a good thermal design, the exposed pad on the ic should solder to a large pad with many vias to the backside ground plane. f sw t t t2 ? i t1 avg. led current hysteretic mode i led v dim figure 2. current-regulator operation
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense _______________________________________________________________________________________ 9 chip information process: bicmos lx lx pgnd 1 2 8 + 7 temp_i dim in gnd cs so-ep top view 3 4 6 5 max16832a max16832c pin configuration d 1 vias for thermal transfer to backside ground plane r sense t off and t on current paths keep this loop tight. led- led+ c filter c in v in lx gnd l figure 3. pcb layout package type package code outline no. land pattern no. 8 so-ep s8e-12 21-0111 90-0150 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. package draw- ings may show a different suffix character, but the drawing per- tains to the package regardless of rohs status.
max16832a/max16832c 2mhz, high-brightness led drivers with integrated mosfet and high-side current sense maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidanc e. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2012 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 5/08 initial release 1 9/08 introduced the max16832c 1 2 5/09 revised general description, features, absolute maximum ratings, and detailed description 1, 2, 5 3 2/10 updated pcb layout guidelines and added figure 3 8, 9 4 8/10 corrected functional diagram and added soldering (reflow) to absolute maximum ratings 2, 5, 6 5 3/12 updated sense voltage threshold high and dim turn-on time in electrical characteristics 2, 3
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