IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 1 ? rev. 00a, 05/20/2014 ? 10-to-150ma constant-current led driver advanced information july 2014 general description the IS31LT3170 and is31lt3171 are adjustable linear current devices with excellent temperature stability. a single resistor is all that is required to set the operating current from 10ma to 150ma. the devices can operate from an input voltage from 2.8v to 42v with a minimal voltage headroom of 0.264v. designed with a low dropout voltage; the device can drive led strings close to the supply voltage without switch capacitors or inductors. the IS31LT3170/71 simplifies designs by providing a stable current without the additional requirement of input or output capacitors, inductors, fets or diodes. the complete constant current driver requires only a current set resistor and a small pcb area making designs both efficient and cost effective. the en pin (1) of the is31lt3171 can function as the pwm signal input used for led dimming purposes. as a current sink it is ideal for led lighting applications or current lim iter for power supplies. the device is provided in a lead (pb) free, sot23-6 package. features ? low-side current sink - current preset to 10ma - adjustable from 10ma to 150ma with external resistor selection ? wide input voltage range from - 2.8v to 42v (is31lt3171) - 5v to 42v (IS31LT3170) with a low dropout of 0.5v ? up to 10khz pwm input (is31lt3171 only) ? protection features: - 0.2%/k negative temperature coefficient for- thermal protection - open circuit and over voltage protection ? up to 1w power dissipation in a small sot23-6 package ? rohs compliant (pb-free) package applications ? linear current sink ? current limiter for power supplies ? led signage ? retail lighting in refrigerator, freezer case and vending machines ? instrumentation led lighting typical application circuit figure 1 typical application circuit
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 2 ? rev. 00a, 05/20/2014 ? pin configuration package pin configuration (top view) sot23-6 pin description no. pin description 1 en enable pin (pwm input is31lt3171 only). 2,3,5 out current sink. 4 gnd ground. 6 rext optional current adjust.
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 3 ? rev. 00a, 05/20/2014 ? ordering information industrial range: -40c to +125c order part no. package qty/reel IS31LT3170-stls4-tr is31lt3171-stls4-tr sot-23-6, lead-free 3000 copyright ? ? ? 2014 ? integrated ? silicon ? solution, ? inc. ? all ? rights ? reserved. ? issi ? reserves ? the ? right ? to ? make ? changes ? to ? this ? specification ? and ? its ? products ? at ? any ? time ? without ? notice. ? issi ? assumes ? no ? liability ? arising ? out ? of ? the ? application ? or ? use ? of ? any ? information, ? products ? or ? services ? described ? herein. ? customers ? are ? advised ? to ? obtain ? the ? latest ? version ? of ? this ? device ? specification ? before ? relying ? on ? any ? published ? information ? and ? before ? placing ? orders ? for ? products. ? integrated ? silicon ? solution, ? inc. ? does ? not ? recommend ? the ? use ? of ? any ? of ? its ? products ? in ? life ? support ? applications ? where ? the ? failure ? or ? malfunction ? of ? the ? product ? can ? reasonably ? be ? expected ? to ? cause ? failure ? of ? the ? life ? support ? system ? or ? to ? significantly ? affect ? its ? safety ? or ? effectiveness. ? products ? are ? not ? authorized ? for ? use ? in ? such ? applications ? unless ? integrated ? silicon ? solution, ? inc. ? receives ? written ? assurance ? to ? its ? satisfaction, ? that: ? a.) ? the ? risk ? of ? injury ? or ? damage ? has ? been ? minimized; ? b.) ? the ? user ? assume ? all ? such ? risks; ? and ? c.) ? potential ? liability ? of ? integrated ? silicon ? solution, ? inc ? is ? adequately ? protected ? under ? the ? circumstances ?
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 4 ? rev. 00a, 05/20/2014 ? absolute maximum ratings (note 1) maximum enable voltage, v en(max) only for IS31LT3170-stls4-tr v en ( max ) only for is31lt3171-stls4-tr 48v 4.5v maximum output current, i out ( max ) 200ma maximum output voltage, v out ( max ) 48v reverse voltage between all terminals, v r 0.5v junction to ambient, ja 191c/w power dissipation, p d ( max ) (note 2) 0.65w maximum junction temperature, t jmax 150c storage temperature range, t stg - 65c ~ +150c operating temperature range, t a ? 40c ~ +125c esd (hbm) esd (cdm) tbd note 1: stresses beyond those listed under ?absolute maximum ratings? ma y cause permanent damage to the device. these are stress rating s only and functional operation of the device at t hese or any other condition beyond those i ndicated in the operational sections of th e specifications is not implied. exposure to absolute maximum rating condi tions for extended periods may affect device reliability. note 2: detail information please refer to package thermal de-rating curve on page 7. electrical characteristics (tbd) test condition is t a = 25c, unless otherwise specified. the symbol in the table means these paramete rs are only available for IS31LT3170-stls4-tr. the symbol in the table means these parame ters are only available for is31lt3171-stls4-tr. symbol parameter condition min. typ. max. unit v bd_out out pin breakdown voltage v en = 0v 40 v i en enable current v en = 24v 1.2 ma v en = 3.3v 1.2 r int internal resistor i rint = 10ma 83.5 95 106.5 ? i out output current v out = 1.4v, v en = 24v 9 10 11 ma v out = 1.4v, v en = 3.3v 9 10 11 output current at r ext = 5.1 ? v out > 2.0v, v en = 24v 150 ma v out > 2.0v, v en = 3.3v 150 v drop voltage drop (v rext ) i out = 10ma 0.08 v dc characteristics with stabilized led load (tbd) test condition is t a = 25c, unless otherwise specified. the symbol in the table means these paramete rs are only available for IS31LT3170-stls4-tr. the symbol in the table means these parame ters are only available for is31lt3171-stls4-tr. symbol parameter condition min. typ. max. unit v smin lowest sufficient supply voltage overhead i out > 18ma 1 v ? i out /i out output current change versus t a v out > 2.0v, v en = 24v -0.2 %/k v out > 2.0v, v en = 3.3v -0.2 output current change versus v s v out > 2.0v, v en = 24v 1 %/v v out > 2.0v, v en = 3.3v 1
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 5 ? rev. 00a, 05/20/2014 ? functional block diagram r int en out rext gnd current mirror
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 6 ? rev. 00a, 05/20/2014 ? typical performance characteristics (tbd)
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 7 ? rev. 00a, 05/20/2014 ? applications information IS31LT3170/71 provides an easy constant current source solution for led lighting applications. it uses an external resistor to adjust the led current from 10ma to 150ma. the led current can be determined by the equation (1): ?? ext int ext int set r r r r i ? ? ? ? ? 065 . 0 15 (1) where r int (96.7 ? typ) is an internal resistor and r ext is the external resistor. paralleling a low tolerance resistor r ext with the internal resistor r int will improve the overall accuracy of the current sense resistance. the resulting output current will vary slightly lower due to the negative temperature coefficient (ntc) resulting from the self heating of the IS31LT3170/71. high input voltage application when driving a long string of leds whose total forward voltage drop exceeds the IS31LT3170 v bd_out limit of 42v, it is possible to stack several leds(such as 2 leds) between the en pin and the out pins 2,3, and 5 so the voltage on the en pin is higher than 5v. the remaining string of leds can then be placed between power supply +v s and en pin, (figure 3). the number of leds required to stack at en pin will depend on the led?s forward voltage drop (vf) and the +v s value. ? figure 3 high input voltage application circuit note: when operating the IS31LT3170 at voltages exceeding the device operating limits, care needs to be taken to keep the en pin and out pin voltage below 42v. thermal protection and dissipation the IS31LT3170/71 implements thermal foldback protection to reduce the led current when the package?s thermal dissipation is exceeded and prevent ?thermal runaway?. the thermal foldback implements a negative temperature coefficient (ntc) of -0.2%/k. the led current can be calculated by equation (2): ? ? 25 % 2 . 0 ? ? ? ? a set led t i i (2) when operating the chip at high ambient temperatures, or when driving maximum load current, care must be taken to avoid exceeding the package power dissipation limits. exceeding the package dissipation will caus e the device to enter thermal protection mode. the maximum package power dissipation can be calculated using the following equation (3): ja a max j max d t t p ? ? ? ) ( ) ( (3) where t j(max) is the maximum junction temperature, t a is the ambient temperature, and ja is the junction to ambient thermal resistance; a metric for the relative thermal performance of a package. the recommended maximum operating junction temperature, t j(max) , is 150c and so the maximum ambient temperature is determined by the package parameter; ja . the ja for the IS31LT3170/71 sot23-6 package, is 191c/w. therefore the maximum power dissipation at t a = - 40c is: w w c c c p max d 1 / 191 40 150 ) ( ? ? ? ? ? ? the actual power dissipation p d is: ) ( out en out d i i v p ? ? ? (4) to ensure the performance, the die temperature (t j ) of the IS31LT3170/71 should not exceed 125c. the graph below gives details for the package power derating. temperature ( c ) power dissipation (w) -40 -25 -10 5 20 35 50 65 80 95 110 125 0 0.2 0.4 0.6 0.8 1 1.2 sot23-6 figure 4 p d vs. t a (sot23-6)
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 8 ? rev. 00a, 05/20/2014 ? classification reflow profiles profile feature pb-free assembly preheat & soak temperature min (tsmin) temperature max (tsmax) time (tsmin to tsmax) (ts) 150c 200c 60-120 seconds average ramp-up rate (tsmax to tp) 3c/second max. liquidous temperature (tl) time at liquidous (tl) 217c 60-150 seconds peak package body temperature (tp)* max 260c time (tp)** within 5c of the specified classification temperature (tc) max 30 seconds average ramp-down rate (tp to tsmax) 6c/second max. time 25c to peak temperature 8 minutes max. figure 5 classification profile
IS31LT3170/71 integrated silicon solution, inc. ? www.issi.com ?? 9 ? rev. 00a, 05/20/2014 ? package information sot23-6 (tbd) note: all dimensions in millimet ers unless otherwise stated.
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