x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m august 2011 rev. 2.2.0 exar corporation www.exar.com 48720 kato road, fremont ca 94538, usa tel. +1 510 668-7000 ? fax. +1 510 668-7001 general description the xrp7618 is an 8-channel, high voltage, constant-current sink led driver capable of sinking up to 100ma curre nt per channel. with outputs rated at 30v, the xrp7618 can control strings of multiple leds with better than 1.5% channel to channel current matching. led channel current is programmed via an external resistor within a 10ma to 100ma range. dimming is supported up to 25khz or through an analog sign al. featuring exar?s smart talk tm technology, when combined with a boost converter, xrp7618 maximizes the overall system efficiency by dynamically reporting the minimum led voltage necessary to maintain current regulation mode. standard configuration the xrp7618evb evaluation board is configured to operate under the following conditions and parameters: input voltage range v cc : .............................. 4.2v ? 5.5v input voltage range v led :....................................... <30v number of le d strings: ..................................... 16 (2x8) led current per string: 3 selectable pre-set levels ............. 20ma-60ma-100ma adj. leve l .......................................... 10ma to 100ma e e v v a a l l u u a a t t i i o o n n b b o o a a r r d d m m a a n n u u a a l l features ? 8 constant-current channels ? adjustable up to 100ma per channel ? channel paralleling for higher current ? 1.5% current matching accuracy ? up to 30v led channel voltage range ? 5v biasing voltage and control ? smart talk tm power optimization ? parallel operations support ? pwm and analog dimming ? uvlo, open led & over temperature protection ? 20-pin tssop (ep) package evaluation board schematics fig. 1: xrp7618 evaluation board schematics
x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m ? 2011 exar corporation 2/7 rev. 2.2.0 pin assignment fig. 2: xrp7618 pin assignment pin description name pin number description chx 1, 2, 3, 4, 7, 8, 9, 10 ch1 to ch8 pins connect an led between each pin and led supply rail voltage (v led ). current value is controlled by r set . connect unused channel(s) to gnd. nc 12 not connected pwm 11 pwm pin this must be held high to enable the output drivers. it can be used for pwm dimming up to 25khz. if not used, connect to v cc . fbx 13 fbx input pin used in parallel configuration as an interface terminal by connecting it to fb pin of the next xrp7618. if not used, leave it unconnected. iset 14 iset pin connect resistor r set from this pin to ground to set led channel current as per i channel =1.194x400/r set fb 15 fb pin samples the led cathode voltage on each channel and outputs the lowest voltage to the step-up converter. sdb 16 sdb output pin sdb signal is synchronous with the pwm signal during pwm dimming. sdb pin outputs low logic to the step-up converter under condit ions such as shutdown or when all channels are inactive. sdbx 17 sdbx input pin used in parallel configuration as an interface terminal by connecting it to sdb pin of the next xrp7618. if not used, connect it to gnd. agnd 18 ground pin vcc 19 input voltage pin must be closely decoupled to gnd pin with a 0.1 f ceramic capacitor. en 20 enable pin this pin must be held high to enable the xrp7618. pgnd 5, 6 ground pin ep exposed pad exposed pad connect to ground ordering information refer to xrp7618?s datasheet and/or www.exar.com for exact and up to date ordering information.
x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m ? 2011 exar corporation 3/7 rev. 2.2.0 using the evaluation board p owering up the xrp7618 c ircuit the xrp7618 evaluation board can be powered from a single +4.2v to +5.5v power supply. connect with short leads directly to the ?vcc? and ?gnd? posts on connector sv1. note the xrp7618 will re main in ?shutdown? until the ?enable? and ?pwm? pins are held high or resistors r11 and r12 are fitted with 0r resistors. led c hannels c urrent s etting the maximum led current per channel (i ledmax ) can be set up to 100ma per channel through the iset pin for each xrp7618 through an extern al resistor r set . the value can be calculated by the following formula: 1.194 400 1.194 the xrp7618 evaluation board implements three switchable preset levels of current per channel (20ma, 60ma and 100ma). these levels are selected via jumpers sv4 and sv5. additionally, resistors r4 and r19 (not populated by default) provide support for a fixed current level (jumpers sv4 and sv5 must be taken off). xrp7618evb comes with the sv4 and sv5 jumpers set to 20ma current setting by default. connect the leds between each channel pin and an external led supply rail voltage (v led ). connect unused channel(s) to gnd. pwm d imming the led current can be adjusted by applying a pwm signal to the pwm pin. in this mode, all enabled channels are adjusted at the same time and brightness is adjusted from 1% to 100% of i ledmax . the supported external pwm signal frequency is 100hz to 25khz. a nalog d imming control besides pwm dimming control, the led current can be controlled continuously (from highest to lowest led current) by raising the voltage at the bottom of rset from 0v normally to 1v max, respectively. rset value may be determined as 1.194 400 where, 1.194v is a typical iset pin voltage, vmod is an adjustment voltage applied to the bottom side of rset, 400 is the typical current multiplication ratio, and i ledmax is the required led current per channel. fig. 3: xrp7618 analog dimming control if adjustment voltage vmod isn?t used, rset resistor should be connected to ground. resistors r5 and r10 (not populated by default) support the analog dimming scheme (jumpers sv4 and sv5 must be taken off). p arallel m ode of o peration multiple xrp7618s can be placed in parallel to drive over 8 strings of leds; unused channels should be tied to ground. xrp7618 evaluation board comes with two xrp7618s connected to each other through their respective fbx and sdbx pins with 0 ? resistors r13 and r14.
x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m ? 2011 exar corporation 4/7 rev. 2.2.0 typical performance characteristics all data taken at v cc = 5v, r iset = 8k ? , t a = 25c, unless otherwise specified - schematic and bom from application information section of this datasheet. fig. 4: current per channel vs temperature fig. 5: pwm dimming: current per channel vs duty cycle fig. 6: current per channel vs input voltage fig. 7: current per channe l vs voltage per channel fig. 8: maximum output current vs voltage per channel fig. 9: current per chan nel vs rset resistor 0 2 4 6 8 10 12 14 16 18 20 0 20 40 60 80 100 current per channel (ma) duty cycle (%) 1khz 100hz 25khz 56 57 58 59 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 current per channel (ma) input voltage (v) 56 57 58 59 0.5 1.0 1.5 2.0 2.5 3.0 current per channel (ma) voltage per channel (v) 10 20 30 40 50 60 70 80 90 100 010203040 current per channel (ma) rset (k ? )
x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m ? 2011 exar corporation 5/7 rev. 2.2.0 evaluation board schematics
x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m ? 2011 exar corporation 6/7 rev. 2.2.0 evaluation board layout fig. 10: components placement & dimensions fig. 11: top side layout fig. 12: bottom side layout bill of material ref. qty manufacturer part number size component eval bd 1 exar corp. 146-6686-02 xrp7618 evaluation board u1, u2 2 exar corp. xrp7618igb-f tssop20 (ep) xrp7618 c1, c2 2 murata corp. grm21br71h104ka01l 0805 ceramic 0.1uf, 50v, x7r r1, r6 2 panasonic corp. erj-3ekf4701v 0603 4.7k ? resistor, 0.1w, 1% r2, r7 2 panasonic corp. erj-3ekf8201v 0603 8.2k ? resistor, 0.1w, 1% r3, r8 2 panasonic corp. erj-3ekf2402v 0603 24k ? resistor, 0.1w, 1% r13, r14 2 panasonic corp. erj-3gey0r00v 0603 0 ? resistor r4, r5, r9, r10, r11, r12 6 0603 not populated sv1, sv2, sv3 3 wurth elektronik 61300811121 conn.head 0.1? 1x8 pin header sv4, sv5 2 wurth elektronik 61300621121 conn.head 0.1? 2x3 pin header sv6 1 wurth elektronik 61300111121 conn.head 0.1? 1x1 pin header
x x r r p p 7 7 6 6 1 1 8 8 8 8 - - c c h h a a n n n n e e l l c c o o n n s s t t a a n n t t c c u u r r r r e e n n t t l l i i n n e e a a r r l l e e d d d d r r i i v v e e r r w w i i t t h h s s m m a a r r t t t t a a l l k k t t m m ? 2011 exar corporation 7/7 rev. 2.2.0 revision history revision date description 1.0.0 08/05/2010 initial release of document 1.1.0 09/22/2010 added evaluation board picture 2.0.0 03/28/2011 added r13 and r14 to isolate fbx and sbdx 2.1.0 07/29/2011 modified schematics c1 and c2 to 100nf 2.2.0 08/18/2011 added default settings information corrected schematics for inclusion of r13 and r14 board revision history board revision date description 146-6686-01 10/29/2010 initial release of evaluation board 146-6686-02 03/28/2011 added r13 and r14 to isolate fbx and sbdx for further assistance email: customersupport@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 ? usa tel.: +1 (510) 668-7000 fax: +1 (510) 668-7030 www.exar.com notice exar corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance 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 make s no representation that the circuits are free of patent infringement. charts and schedules contained here in are only for illustr ation purposes and may vary depending upon a user?s specific application. while the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. exar corporation does not recommend the us e of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause fa ilure of the life support system or to significantly affect it s 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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