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x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r december 2012 rev. 1.2.0 exar corporation www.exar.com 48720 kato road, fremont ca 94538, usa tel. +1 510 668 - 70 00 C fax. +1 510 668 - 70 01 general description the xrp 7613 is a non - synchronous step down converter with integrated fet optimized to drive high power leds at up to 1 .2 a of continuous current. a wide 7.0 v to 36 v input voltage range allows for single supply operations from industry standard 12v , 18v or 24v power rails. based on a hysteretic pfm control scheme, the xrp7613 can operate at switching frequency of up to 1mhz and allows for small external components selection while providing very fast transient response and achieving excellent efficiency. the output current is programmable from 150ma to 1.2a through an external sense resistor. output current d imming is supported through an analog signal or pwm logic signal at up to 40khz. a dynamic led current thermal control further enhances the reliability of the end application by linearly reducing the led current as temperature raises. a n open led, led short circuit, over temperature and under voltage lock out protection i nsures safe operations under abnormal operating conditions. the xrp 7613 is offered in rohs compliant, green/halogen free 8 - pin exposed pad soic package. applications ? general lighting and displays ? architectural and accent lighting ? medical and industrial instrumentation ? video projectors features ? 1.2a continuous output led current ? 150ma to 1.2a programmable range ? 7 v to 36v single rail input voltage ? pwm & analog dimming capability ? up to 40khz frequency ? led current foldback thermal control ? selectable automat ic linear dimming of led current with temperature ? shutdown control ? built - in soft start ? open led, led short circuit and over temperature protections ? rohs compliant green/halogen free 8 - pin exposed pad so ic package typical application diagram fig. 1 : xrp7613 application diagram s
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 2 / 13 rev. 1.2.0 absolute maximum rat ings these are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. input voltage v in ................................ .................... 40 v isen voltage ................................ (v in +0.3v) to (v in - 5v) en/dim voltage ................................ ............ - 0.3v to 5v junction temperature ................................ .......... 150c storage temperature .............................. - 65c to 150c lead temperature (soldering, 10 sec) .................... 260c esd rating (hbm - human body model) .......................... all pins ................................ ................................ 2kv operating ratings input voltage range v in ................................ ...... 7 v - 36 v operating temperature range ................... - 40c to 85 c thermal resistance ................................ ...................... ? ja 1 ................................ ............................... 60 c/w ? j c 1 ................................ ............................... 15 c/w note 1: package is placed on 2 - layer pcb with 2 ounces copper and 2 square inch, connected with 8 vias. electrical specifica tions specifications with standard type are for an operating ambient temperature of t j = t a = 25c only; limits applying over the full operating ambient temperature range are denoted by a ? . minimum and maximum limits are guaranteed through test, design, or statistical correlation. typical values represent the most likely parametric norm at t a = 25c, and are provided for reference purposes only. unless otherwise indicated, v in = 12 v , l=47 h , 1 x led and i led = 330 ma and t a = 25 c. parameter min. typ. max. units conditions quiescent current 0.5 1 ma output switching en/dim floating, f=250khz 35 45 a output not swithing en/dim<0.2v mean current sense threshold voltage 95 100 105 mv measured on isen pin with respect to v in . isen threshold hysteresis - 15 +15 % i led output current range 150 1200 ma v in =12v efficiency 93 % v in =12v, v out =7.2v, l=47f, i led =330ma switch on resistance r ds(on) 0.5 sw 35 0 khz en/dim floating, l=47f, i led =330ma ,1xled minimum switch on time 180 ns minimum switch off time 280 n s vref voltage 2.46 2.5 2.54 v vref output current 250 a recommended duty cycle range at f sw_max 30 70 % under voltage lock out threshold 6 v v in rising 5.5 v in falling maximum dimming frequency 40 khz en/dim input level logic high 1.3 v en/dim input level analog 0.4 1.25 v en/dim input level logic low 0.2 v en/dim shutdown delay 16 m s en/dim pull up current 3.7 a thermal shutdown temperature 150 c thermal shutdown hysteresis 30 c thermal regulation input level 0.4 v r 1 =10k th =1.91k 1 =10k, r th =1.265k
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 3 / 13 rev. 1.2.0 block diagram fig. 2 : xrp7613 block diagram pin assign ment fig. 3 : xrp7613 pin assign ment p g n d 1 l x 8 x r p 7 6 1 3 h s o i c - 8 v i n 2 e n / d i m 4 i s e n 3 g n d 7 v r e f 6 t h 5
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 4 / 13 rev. 1.2.0 pin description name pin description pgnd 1 power ground pin. vin 2 power supply input pin. place an input decoupling capacitor as close as possible to this pin. ise n 3 led current setting pin. connect resistor rset from this pin to vin (pin 2) to define nominal average led current. en/dim 4 dimming and enable pin. for automatic startup, leave pin floating. th 5 led temperature protection sense input. connect temperature thermal sense resistors to turn off output current above a preset temperature threshold. vref 6 reference voltage for thermal protection. gnd 7 ground pin. lx 8 connect to the output inductor. gnd exposed pad power ground pin. ordering information part number ambient temperature range marking package packing quantity note 1 note 2 xrp7613idbtr - f - 40ct a +125c xrp7613i yywwf x hsoicn - 8 exp. pad 2.5k/tape & reel halogen free xrp7613evb xrp7613 evaluation board yy = year C ww = work week C x = lot number when applicable.
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 5 / 13 rev. 1.2.0 typical performance characteristics fig. 4 : efficiency versus input voltage fig. 5 : efficiency versus input voltage fig. 6 : v set versus input voltage at i led =330ma fig. 7 : v set versus input voltage at i led =770ma fig. 8 : v set versus input voltage at i led = 1.1 a fig. 9 : led current versus en/dim voltage 95 100 105 110 115 120 0 10 20 30 40 v set (mv) v in (v) i led = 330ma l = 47h 2xled 1xled 3xled 95 100 105 110 115 120 0 10 20 30 40 v set (mv) v in (v) i led = 770ma l = 47h 2xled 3xled 1xled 95 100 105 110 115 120 0 10 20 30 40 v set (mv) v in (v) i led = 1.1a l = 47h
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 6 / 13 rev. 1.2.0 fig. 10 : thermal regulation fig. 11 : thermal regulation threshold versus temperature fig. 12 : switch waveform v in =12v, i led =350ma, 3 leds fig. 13 : switch waveform v in =12v, i led =700ma, 1 led fig. 14 : pwm dimming v in =24v, duty cycle = 50%, f pwm =40khz fig. 15 : short circuit v in =12v
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 7 / 13 rev. 1.2.0 fig. 16 : frequency versus input voltage , i led =330ma fig. 17 : frequency versus input voltage , i led = 77 0ma fig. 18 : frequency versus input voltage , i led = 1.1 a fig. 19 : pwm dimming at 25khz, v in =24v, 3xled, l=47 h 0 100 200 300 400 500 600 700 0 10 20 30 40 f (khz) v in (v) i led = 330ma l = 47h 1xled 2xled 3xled 0 100 200 300 400 500 0 10 20 30 40 f (khz) v in (v) i led = 770ma l = 47h 1xled 2xled 3xled 0 50 100 150 200 250 300 350 0 10 20 30 40 f (khz) v in (v) i led = 1.1a l = 47h 2xled 3xled 1xled 0 20 40 60 80 100 0 20 40 60 80 100 % i out % dutycycle iled = 1.1a iled = 0.347a
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 8 / 13 rev. 1.2.0 application informat ion h ysteretic o peration the xrp7613 is a hysteretic step - down led driver . it uses 15% double - en ded hysteresis to regulate the average led current to the value programmed by rs e t (refer to figure 1) . the 15% hysteresis is achieved with resistors r2 and r3 in the block diagram shown in figure 2. average i nternal current through r1, r2 and r3 is given by i int (avg) =0.1v/r1 . note that voltage across r set must be the same as voltage across r 1 . therefore average led current should be i led (avg) =0.1v/r set . during off time fets n1 and n2 are off. inductor current i l ramps down through the external schottky diode and voltage at isen decreases . this, in turn, causes the i int to decrease. when i int falls 15% below i int (avg) , comparator is triggered on (note that this should correspond to i led falling 15% below i led (avg) ) . n1 and n2 turn on and on time comm ences. n2 shorts r3 and thereby require s a higher i int in order to trigger the comparator off . n1 shorts the inductor to ground, i l ramps up and voltage at isen increases . this causes the i int to increase. when i int rises 15% above i int (avg) , comparator is triggered off and the cycle repeats. t urn o n and t urn o ff d elay as explained above when i int falls 15% below i int (avg) , the comparator is triggered on . however, i t takes 280ns (nominal) before n1 turns on and lx transitions from high to low voltage (refer to figure 20 ) . the turn on delay time results in inductor current ripple i l to exceed the - 15% hysteresis set by the internal control. because t his delay imposes a lower bound on the n1 off time , it has been called minimum switch off time in the electrical specifications table . when i int rises 15% above i int (avg) , the comparator is triggered o ff. there is , however, a delay of 180ns before n1 turns o ff and lx transitions from low to high voltage. the turn off delay time results in i l exceeding the +15% hysteresis set by the internal control. because this delay imposes a lower bound on the n1 on time , it has been called minimum switch on time in the electrical specifications table. th us the delay times will cause t he switching frequency to be lower than expected because the turn on and turn off time will take longer to complete. graphs of typic al switching frequency versus v in for various operating conditions are shown in figures 16 - 18. the delay times , under some operating conditions , may force the average current to deviate from i led (avg) =0.1v/r set if they cause asymmetric hysteresis . as an example in figure 20 the positive hysteresis is higher than the negative hysteresis and there is a positive offset . a verage current is higher than 0.1v/r set . the effect of delay times on average current has been taken into account by measuring the vo ltage across r set for various operating conditions. graphs of v set versus v in are shown in (figures 6 - 8). fig. 20 : effect of delay time s on inductor and led current ripple and a verage c urrent s hutdown c ontrol a shutdown control function is provided through the en/dim input pin. connecting the en/dim input pin to ground or to a dc voltage lower than 200mv for longer than 20ms will completely shut down the xrp7613. in this state, the quiescent current is l ess than 35a and the internal reference, error amplifier, comparators, and biasing circuitry completely turned off. 0 . 1 v / r s e t + 1 5 % - 1 5 % l x t u r n o n d e l a y = 2 8 0 n s t u r n o f f d e l a y = 1 8 0 n s i l ( a v g )
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 9 / 13 rev. 1.2.0 s etting the led c urrent the output current i led of xrp7613 can be set by the external sense resistor r set . the relationship between i led and r set is v set can be determined from graphs in figure s 6 - 8 . as an example for the operating conditions i led =350ma, v in =24v, 3xled; v set =105mv from figure 6. o perating f requency the operating frequency of the xrp7613 can be ca lculated from the following equation where f s is the operating frequency, t on is the switch on time and t off is the switch off time. the switch on time can be approximated from the following equation the switch off time can be approximated from the following equation where v in is the input voltage v led is the total led forward voltage i led is the led average current r set is current sense resistance r l is inductor resistance r ds (on) is switch on resistance (0.5 typ.) l is the inductor value i l is the inductor peak to peak current v d is diode forward v oltage at the led average current. the recommended operating frequency should not exceed 1mhz. d imming c ontrol the xrp7613 offers t wo ways of achieving led dimming: standard pwm dimming and analog dimming. the en/dim input pin is used not only to control t he xrp7613 shutdown but also the pwm and analog dimming functions. if dimming and/or shutdown controls are not required, the en/dim pin can be left floating for automatic turn on upon application of proper v in . pwm dimming a logic - level pwm signal applied to the en/dim pin can be used for pwm dimming control of the led s . this external signal turns the mosfet gate drive on and off, thereby modulating the average current delivered to the led proportional to the duty cycle of the pwm signal . the en/ dim signal will shutdown the xrp7613 when en/ dim = l and turn - on the xrp7613 when dim = h . the dim signal needs to be greater than 1.3 v minimum to turn - on and less than 200mv to fully turn - o ff the device . the maximum allowed pwm dimming frequency that can be applied is 40 khz. analog dimming t he average current delivered to the led , ie the led brightness, can also be controlled by applying a variable dc voltage signal to the en/dim pin. a dc voltage greater than 1.25v will drive output led current to 100% of the led c urrent as set by the external sense resistor r set while a voltage lower than 200mv will shutdown the xrp7613. when analog dimming is required, the dc voltage range of en/dim s hould be between 0.4v to 1.25v in order modulating the average current delivered to the led accordingly .
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 10 / 13 rev. 1.2.0 p rotections led open circuit protection upon detection of an open - circuit on any led connected to the xrp7613, the device will shut down. led short circuit protection upon detecting a short - circuit on any led connected to the xrp7613, the device will maintain the led current as set by the external sense resistor r set . uvlo protection the xrp7613 has a n u nder v oltage l ock - out comparator to monitor the input voltage v in . the v in uvlo threshold is set internally: w hen v in pin is greater than 6.0 v the xrp 7613 is permitted to start up pending t he removal of all other faults. led thermal protection the xrp7613 includes a led thermal regulation circuit to prevent an over temperature situation on the led. wh en the led temperature rises above a predefined threshold, the xrp7613 will reduce linearly the led current from its nominal set value. fig. 21 : v th voltage the xrp7613 continuously monitor s the led temperature by measuring the vo ltage on its th pin . the v th voltage is created through a resistive network of a negative temperature coefficient (ntc) thermistor r th and a fixed resistor r t between vref pin and ground. by setting r t =10k? and using a 103kt1608 thermistor, the voltage on the th pin will reduce to 0.4v when the led temperature reaches 70c. the led average current will be decreased linearly when v th is between 0.4v and 0.28v. if the led temperature is over 90c, the voltage on the th pin will reduce to 0.28v and the led wi ll be turned off in order to decrease the led temperature. when the voltage on the th pin rises to 0.3v, the led will be turned on again. if the led thermal regulation function isnt required, the th pin should be connected directly to vref pin to disable this function. d iode s election schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for any xrp7613 applications. the forward voltage drop of a schottky diode represents the conduction losses in the diode, w hile the diode capacitance (ct or cd) represents the switching losses. for diode selection, both forward voltage drop and diode capacitance need to be considered. schottky diodes with higher current ratings usually have lower forward voltage drop and large r diode capacitance, which can cause significant switching losses. a schottky diode with a 2a current rating is adequate for most xrp7613 applications. i nput c apacitor s election ceramic capacitors with their low esr values and small size are ideal for the xrp7613 applications. when selecting an input capacitor, a low esr capacitor is required to minimize the noise at the device input. it may be necessary to add an extra small value ceramic type capacitor in parallel with the input capacitor to prevent any p ossible ringing. i nductor s election recommended inductor values for the xrp7613 are in the range of 22h to 68 h. the inductor selected should have low core losses and low dcr.
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 11 / 13 rev. 1.2.0 l ayout c onsideration for proper operations of xrp7613, the following guidelines should be followed. 1.the input capacitor should be placed as close as possible to the v in pin in order to reduce the input voltage ripple and noise. 2.the inductor, internal power switch, schottky diode, output capacitor and the leds should be kept as close as possible. 3. pcb traces with large current should be kept short and wide. 5. e ffect from noise can be reduced by placing the xrp7613 gnd pin as close as possible to the ground pin of the input bypass capacitor. 6.the isen pin and vin pin sho uld be connected to the sense resistor directly . traces should be routed away from any potential sources. 7.the vref pin and th pin should be connected to the led thermal sense resistors directly . traces should be routed away from any potential sources. t ypical a pplication c ircuits fig. 22 : typical application diagram
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 12 / 13 rev. 1.2.0 package specificatio n 8 - p in e xposed p ad soic
x x r r p p 7 7 6 6 1 1 3 3 1 1 . . 2 2 a a 3 3 6 6 v v s s t t e e p p d d o o w w n n h h i i g g h h b b r r i i g g h h t t n n e e s s s s l l e e d d d d r r i i v v e e r r ? 2012 exar corporation 13 / 13 rev. 1.2.0 revision history revision date description 1.0.0 11/09 / 2012 initial release of d ata s heet 1.1.0 11/26/2012 corrected typographical error l=47h in electrical specification conditions. 1.2.0 12/ 10 /2012 added explanation to hysteretic operation and turn on and turn off delay time . for further assistan ce email: customersupport@exar.com powertechsupport@exar.com exar technical documentation: http://www.exar.com/techdoc/default.aspx? e xar c orporation h eadquarters and s ales o ffices 48720 kato road fremont, ca 94538 C notice exar corporation reserves the right to make changes to the products contained in this publication in order to improve design, performa nce or reliability. exar corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. charts and sched ules contained herein are only for illustration purposes and may vary depending upon a users specific application. while the information in this publication has been carefully checked; no responsibility, however , is assumed for inaccuracies. exar corporat ion 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 exar corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of exar corporation is adequately protected under the circumstances. reproduction, in part or whole, without the prior written consent of exar corporation is prohibited.
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