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device description the ZXSC310 is a single or multi cell led driver designed for lcd backlighting applications. the input voltage range of the device is between 0.8v and 8v. this means the ZXSC310 is compatible with single nimh, nicd or alkaline cells, as well as multi-cell or liion batteries. the device features a shutdown control, resulting in a standby current less than 5a, and an output capable of driving serial or parallel led?s. the circuit generates constant power output, which are ideal for driving single or multiple led?s over a wide range of operating voltages. these features make the device ideal for driving led?s particularly in lcd backlight applications for digital still cameras and pda?s. features 94% efficiency minimum operating input voltage 0.8v maximum operating input voltage 8v standby current less than 5a programmable output current series or parallel led configuration low saturation voltage switching transistor sot23-5 package applications lcd backlights: digital still camera pda mobile phone led flashlights and torches white led driving multiple led driving the ZXSC310 is a pfm dc-dc controller ic that drives an external zetex switching transistor with a very low saturation resistance. these transistors are the best switching devices available for this type of conversion enabling high efficiency conversion with low input voltages. the drive output of the ZXSC310 led driver generates a dynamic drive signal for the switching transistor. the circuit can start up under full load and operates down to an input voltage of 0.8 volts. the solution configuration ensures optimum efficiency over a wider range of load currents; several circuit configurations are possible depending on battery life versus brightness considerations. the ZXSC310 is offered in the sot23-5 package which, when combined with a sot23 switching transistor, generates a high efficiency small size circuit solution. the ic and discrete combination offers the ultimate cost vs performance solution for led backlight applications. ZXSC310 issue 1 - september 2002 1 led driver solution for lcd backlighting v in v cc v =3.3v/5v drive i sense gnd s tdn typical applications circuit device reel size tape width quantity per reel ZXSC310e5 180mm 8mm 3000 ordering information device markings c310
absolute maximum ratings: supply voltage -0.3 to 10v maximum voltage other pins -0.3 to v cc +0.3v power dissipation 450mw operating temperature -40 to 85 c storage temperature -55 to 125c ZXSC310 issue 1 - september 2002 2 symbol parameter conditions min typ max units efficiency 1 94 % v cc recommended supply voltage range 0.8 8 v v cc(min) minimum startup and operating voltage i drive =-600a , v drive =0.7v i drive =-600a, v drive =0.7v, t amb =-10c3 0.8 0.9 0.92 v i q quiescent current 2 v en = v cc (enabled) v en = 0v (standby) 0.2 45 ma a i vdrive base drive current v drive = 0.7v, v isense = 0v 1.5 3.5 ma i cc supply current 3 v drive = 0.7v, v isense =0v 2 4 ma v vdrive(high) high level drive voltage v isense =0v,i vdrive =-0.5ma v cc -0.3 v cc v v vdrive(low) low level drive voltage v isense = 50mv, i vdrive = 5ma 0 0.2 v v stdn(high) device enabled 0.7 v v stdn(low) device in standby mode 0.15 v i stdn enable input current -1 1 a v isense (threshold) output current reference voltage 14 19 24 mv t cvisense i sense voltage temp co. 2 0.4 %/c i isense i sense input current v isense = 0v 0 -30 -65 a electrical characteristics: test conditions unless otherwise stated: v cc =1.5v, t amb =25 c symbol parameter conditions min typ max units t drv discharge pulse width 1.2 1.7 3.2 s f osc recommended operating frequency 4 200 khz electrical characteristics: ac parameters 2 test conditions unless otherwise stated: v cc =1.5v, t amb =0 to 70 c 1 application dependent, see reference designs 2 these parameters guaranteed by design 3 total supply current =i q +i vdrive , see typical characteristics 4 operating frequency is application circuit dependent. see applications section.
fmmt618 for the circuits described in the applications section zetex fmmt618 is the recommended pass transistor. zhcs1000 for the maximum brightness circuit described in the applications section zetex zhcs1000 is the recommended schottky diode. the following indicates outline data for the device, more detailed information can be found in the zetex surface mount products data book or on zetex web page: www.zetex.com the following indicates outline data for the zhcs, more detailed information can be found on zetex web page: www.zetex.com ZXSC310 issue 1 - september 2002 3 symbol parameter conditions min typ max units v ce(sat) collector-emitter saturation voltage 5 i c =0.1a, i b =10ma i c =1a, i b =10ma i c =2.5a, i b =50ma 8 70 130 15 150 200 mv v (br)ceo collector-emitter breakdown voltage 5 i c =10ma 20 27 v electrical characteristics: test conditions unless otherwise stated: t amb =25 c 5 measured under pulse conditions. pulse width=300s. duty cycle 2% symbol parameter conditions min typ max units v f forward voltage i f = 500ma i f =1a 400 500 mv t rr reverse recovery time switched from i f =500ma to i r =500ma. measured at i r =50ma 12 ns i r reverse current v r = 30v 50 100 a electrical characteristics: test conditions unless otherwise stated: t amb =25 c part number v r i f i fsm v f at i r at capacitance at v r = 25v, f = 1mhz package max. v max. ma max. a max. mv i f ma max. a v r v typ. pf sot23 bat54 30 200 0.6 500 30 250 25 10 sot23-6 zhcs2000 40 2000 20 500 2000 1000 30 60 sot23 zhcs1000 40 1000 12 500 1000 100 30 25 sot23 zhcs750 40 750 12 540 750 100 30 25 sot23 zhcs500 40 500 6.75 550 500 40 30 20 sot23 zhcs400 40 400 6.75 500 400 40 30 20 sot323
ZXSC310 issue 1 - september 2002 4 typical characteristics
device description the ZXSC310 is pfm, controller ic which, when combined with a high performance external transistor, enables the production of a high efficiency boost converter for led driving applications. a block diagram is shown for the ZXSC310 below. the on chip comparator forces the driver circuit and therefore the external switching transistor off if the voltage at i sense exceeds 19mv. an internal reference circuit and divider set this threshold. the voltage at i sense is taken from a current sense resistor connected in series with the emitter of the switching transistor. a monostable following the output of the comparator forces the turn-off time of the output stage to be typically 1.7us. this ensures that there is sufficient time to discharge the inductor coil before the next on period. with every on pulse the switching transistor is kept on until the voltage across the current-sense resistor exceeds the threshold of the i sense input. the on-pulse length, and therefore the switching frequency, is determined by the programmed peak current, the input voltage and the input to output voltage differential. see applications section for details. the driver circuit supplies the external switching transistor with a fixed drive current. to maximise efficiency the external transistor switched quickly, typically being forced off within 30ns. ZXSC310 issue 1 - september 2002 5 d rive i sense r2 v re r1 v drive g n i v cc s tdn ZXSC310 block diagram
reference designs three typical led driving applications are shown. firstly a typical lcd backlight circuit, then maximum brightness led driving solution and lastly an optimised battery life led driving solution. this application shows the ZXSC310 in a typical lcd backlight application for digital still cameras and pda?s. the input voltage for these backlight circuits are usually fixed from the main system power, typically 3.3v or 5v. the led?s are connected serially so that the light is distributed uniformly in each led. the current provided to the led?s can either be pulsed or dc. the dc current is programmable via a sense resistor, r sense , and is set to an optimum led current of 20ma for the reference designs. dc current is achieved by adding a schottky rectifying diode and an output capacitor, as shown in the reference design below. ZXSC310 issue 1 - september 2002 6 v in v cc v =3.3v/5v drive i sense gnd s tdn lcd backlight circuit ref value part number manufacture comments u1 n/a ZXSC310e5 zetex plc single cell converter, sot23-5 q1 n/a fmmt618 zetex plc low v ce(sat ) npn, sot23 d1 n/a zhcs1000 zetex plc 1a schottky diode, sot23 c1 2.2 f generic various 0805 size r1 6 150m generic various 1206 size r1 7 250m generic various 1206 size l1 8 68h surface mount inductor materials list 6 used for 3.3v input, i led set to 20ma 10%. 7 used for 5v input, i led to 20ma 10%. 8 see application section. (notes)
ZXSC310 issue 1 - september 2002 7 this circuit provides a continuous current output to the led by rectifying and buffering the dc-dc output. this ensures maximum led brightness. ref value part number manufacture comments u1 n/a ZXSC310e5 zetex plc single cell converter, sot23-5 q1 n/a fmmt617 zetex plc low vce(sat) npn, sot23 d1 1a zhcs1000 zetex plc 1a shottky diode, sot23 r1 100m generic various 0805 size c1 2.2 f generic various low esr ceramic capacitor l1 100h 8 surface mount inductor materials list 8 see application section. batt maximum brightness solution (notes)
to ensure optimum efficiency, and therefore maximum battery life, the led is supplied with a pulsed current. maximum efficiency is ensured with the removal of rectifier losses experienced in the maximum brightness solution . ZXSC310 issue 1 - september 2002 8 ref value part number manufacture comments u1 n/a ZXSC310e5 zetex plc single cell converter, sot23-5 q1 n/a fmmt617 zetex plc low v ce(sat) npn, sot23 r1 330m generic various 0805 size l1 100 h 8 surface mount inductor materials list 8 see application section. maximum battery life solution (notes)
applications information the following section is a design guide for optimum converter performance. switching transistor selection the choice of switching transistor has a major impact on the converter efficiency. for optimum performance, a bipolar transistor with low v ce(sat) and high gain is required. the zetex fmmt618 is an ideal choice of transistor, having a low saturation voltage. a data sheet for the fmmt618 is available on zetex web site or through your local zetex sales office. outline information is included in the characteristics section of this data sheet. schottky diode selection for the maximum battery life solution a schottky rectifier diode is not required. as with the switching transistor the schottky rectifier diode has a major impact on the converter efficiency. a schottky diode with a low forward voltage and fast recovery time should be used for this application. the diode should be selected so that the maximum forward current is greater or equal to the maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output voltage. the zetex zhcs1000 meets these needs. datasheets for the zhcs series are available on zetex web site or through your local zetex sales office. outline information is included in the characteristics section of this data sheet. for the maximum brightness solution a pulsed current is supplied to the led and thus a schottky rectifier diode is required. inductor selection the inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. for the lcd backlight reference design we recommend an inductor value of 68uh with a core saturation current rating greater than the converter peak current value and low series resistance. inductor selection has a significant impact on the converter performance. for applications where efficiency is critical, an inductor with a series resistance of 500m or less should be used. a list of recommended inductors is shown in the table below: ZXSC310 issue 1 - september 2002 9 0. 0 0.4 0. 1 0.2 0. 3 part no. manufacture l i pk r dc do1608c-683 coilcraft 68 h 0.4a 0.86 cr54-680 sumida 68 h 0.61a 0.46 p1174.683 pulse 68 h 0.4a 0.37 sfop5845-r61680 samwha 68 h 0.61a 0.46 sis43-680 delta 68 h 0.4 1.125
peak current definition the peak current rating is a design parameter whose value is dependent upon the overall application. for the high brightness reference designs, a peak current of was chosen to ensure that the converter could provide the required output power to the led. in general, the i pk value must be chosen to ensure that the switching transistor, q1, is in full saturation with maximum output power conditions, assuming worse-case input voltage and transistor gain under all operating temperature extremes. once i pk is decided the value of r sense can be determined by: a selection guide of sense resistor and inductor values for given input voltages, output currents and number of led connected in series is provided in the table below. ZXSC310 issue 1 - september 2002 10 r v i sense isense pk = input voltage (v) led current (ma) no. of led?s r sense (m ) inductor ( h) efficiency (%) 3.3v 10 3 510 68 80 3.3v 10 4 330 68 81 3.3v 10 6 150 68 79 3.3v 20 3 220 68 84 3.3v 20 4 150 68 93 3.3v 20 6 77 68 79 3.3v 30 3 170 68 84 3.3v 30 4 100 68 84 3.3v 30 6 47 68 77 5v 10 3 750 68 83 5v 10 4 510 68 84 5v 10 6 330 68 79 5v 20 3 440 68 85 5v 20 4 250 68 85 5v 20 6 150 68 82 5v 30 3 330 68 86 5v 30 4 170 68 85 5v 30 6 100 68 83
output power calculation by making the above assumptions for inductance and peak current the output power can be determined by: note:v out =output voltage + schottky rectifier voltage drop. where t off ? 1.7us (internally set by ZXSC310) and and where operating frequency can be derived by: capacitor selection for pulsed operation, as in the maximum battery life solution, no capacitors are required at the output to the led. for rectified operation, as in the maximum brightness solution, a small value ceramic capacitor is required, typically 2.2uf. generally an input capacitor is not required, but a small ceramic capacitor may be added to aid emc, typically 470nf to 1uf. (notes) ZXSC310 issue 1 - september 2002 11 () ii vvt l min pk out in off =? ? () f tt on off = + 1 i ii av pk min = + 2 () t tv v v on off out in in = ? pvvi t tt out out in av off on off =? + ()
shutdown control the ZXSC310 offers a shutdown mode that produces a standby current of less than 5ua when in operation. when the voltage at the s tdn pin is 0.7v or higher the ZXSC310 is enabled, hence the driver is in normal operation. when the voltage at the s tdn pin is 0.1v or lower the ZXSC310 is disabled, hence the driver is in shutdown mode. if the s tdn pin is open circuit the ZXSC310 is also enabled. layout of lcd backlighting solution demonstration board a demonstration board for the lcd backlighting solution, is available upon request. these can be obtained through your local zetex office or through zetex web pages. for all reference designs gerber files and bill of materials can be supplied. ZXSC310 issue 1 - september 2002 12 top silk drill file top copper bottom copper
ZXSC310 issue 1 - september 2002 13 stdn vcc gnd isense vdrive 1 2 3 4 5 top view pinout diagram pin no. name description 1v cc supply voltage, generally alkaline, nimh or nicd single cell 2g nd ground 3s tdn shutdown 4i sense inductor current sense input. internal threshold voltage set to 19mv. connect external sense resistor 5v drive drive output for external switching transistor. connect to base of external switching transistor. pin descriptions
(notes) ZXSC310 issue 1 - september 2002 14
(notes) ZXSC310 issue 1 - september 2002 15
ZXSC310 issue 1 - september 2002 16 europe zetex plc fields new road chadderton oldham, ol9 8np united kingdom telephone (44) 161 622 4422 fax: (44) 161 622 4420 uk.sales@zetex.com zetex gmbh streitfeldstra ? e19 d-81673 m nchen germany telefon: (49) 89 45 49 49 0 fax: (49) 89 45 49 49 49 europe.sales@zetex.com americas zetex inc 700 veterans memorial hwy hauppauge, ny11788 usa telephone: (631) 360 2222 fax: (631) 360 8222 usa.sales@zetex.com asia pacific zetex (asia) ltd 3701-04 metroplaza, tower 1 hing fong road kwai fong hong kong telephone: (852) 26100 611 fax: (852) 24250 494 asia.sales@zetex.com these offices are supported by agents and distributors in major countries world-wide. this publication is issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. the company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. for the latest product information, log on to www.zetex.com ? zetex plc 2002 dim millimetres inches min max min max a 0.90 1.45 0.035 0.057 a1 0.00 0.15 0.00 0.006 a2 0.90 1.3 0.035 0.051 b 0.35 0.50 0.014 0.020 c 0.09 0.20 0.0035 0.008 d 2.80 3.00 0.110 0.118 e 2.60 3.00 0.102 0.118 e1 1.50 1.75 0.059 0.069 e 0.95 ref 0.037 ref e1 1.90 ref 0.075 ref l 0.10 0.60 0.004 0.024 a 010010 sot23-5 package dimensions sot23-5 package outline

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