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1 semiconductors description the ZXLD1100 is a pfm inductive boost converter designed for driving 2, 3 or 4 series connected white leds from a li-ion cell and up to 8 leds from a 5v supply. the device operates from an input supply of between 2.5v and 5.5v and provides an adjustable output current of up to 50ma. the ZXLD1100 includes the output switch and peak current sense resistor, and can operate with a maximum output voltage of 28v. quiescent current is typically 60 a and a shutdown function is provided to reduce this current to less than 500na in the 'off' state. advanced features ? internal 30v ndmos switch, current sense and open circuit protection ? true analog dimming via pwm features ? low profile sc70 6 pin package ? internal pwm filter for flicker free output ? high efficiency (80% typ) ? wide input voltage range: 2.5v to 5.5v ? up to 50ma output current ? low quiescent current: (60 a typ) ? 500na maximum shutdown current ? up to 1mhz switching frequency ? low external component count ? inherently matched led currents output current can be adjusted by applying a pwm control signal to the 'enable' pin. depending upon the control frequency, this will provide either a continuous or a 'chopped' output current. the pwm filter components are contained within the chip. the ZXLD1100 contains an internal avalanche diode to protect the output switch. this allows the device to operate indefinitely if the load is open circuit. input supply current during this condition is less than 1ma. the device is assembled in a low profile sc70-6 pin package with industry standard pinout. applications ? mobile phones ? digital cameras ? pdas ? lcd modules ? portable internet appliances ? palmtop computers ZXLD1100 issue 2 - february 2004 adjustable led driver with internal switch and open circuit protection in sc70-6 pin connections typical application circuit
ZXLD1100 semiconductors issue 2 - february 2004 2 parameter symbol limit unit input voltage (v in )7v lx output voltage (v lx )30v switch output current (i lx ) 500 ma power dissipation (pd) 300 mw operating temperature (t op ) -40 to 85 c storage temperature (t st ) -55 to 150 c junction temperature (t j max ) 125 c absolute maximum ratings (voltages to gnd unless otherwise stated) device device description temperature range part mark taping options ZXLD1100h6 boost convertor in sc70-6 -40 to +85c 110 ta, tc ordering information ZXLD1100h6ta = 7? reel of 3,000 devices ZXLD1100h6tc = 7? reel of 3,000 devices
ZXLD1100 semiconductors issue 2 - february 2004 3 symbol parameter conditions min. typ. max. unit v in input voltage 2.5 5.5 v i in supply current quiescent shutdown v en =v in ,i lx =0, output not switching v en =0v 60 100 500 a na v fb fb pin control voltage 90.5 109.5 mv i fb fb pin input current 100 na f lx operating frequency l=10 h, v out =10v, i out =20ma 0.35 1 mhz t off lx output 'off' time 350 500 ns t on lx output 'on' time (2) 5s i lxpk switch peak current limit l=10 h, v out =10v, i out =20ma 320 ma r lx switch 'on' resistance 1.5 i lx(leak) switch leakage current v lx =20v 1 a v out controller output voltage normal operation vsense pin open-circuit or grounded 28 v v out(max) controller output voltage with output open circuit (3) vsense connected to vout 25 30 v v enh en pin high level input voltage device active 1.5 v in v v enl en pin low level input voltage device in shutdown 0.4 v i enl en pin low level input current v en =0v -100 na i enh en pin high level input current v en =v in 100 na t en(hold) en pin turn off delay (4) v en switched from high to low 80 120 s ? t/t pwm duty cycle range at ?en? input for filtered pwm control (5) 10khz < f < 100khz, v enh =v in 20 100 % f lpf internal pwm low pass filter cut-off frequency 4 khz a lpf filter attenuation f=30khz 52.5 db electrical characteristics (at t amb = 25c unless otherwise stated (1) ) notes: (1) production testing of the device is performed at 25c. functional operation of the device over a -40c to +85c temperature range is guaranteed by design, characterization and process control. (2) nominal 'on' time (t onnom ) is defined by the input voltage (v in ), coil inductance (l) and peak current (i lxpkdc ) according to the expression: t onnom = {i lx(pkdc ) x l/v in } +200ns. (3) when using the open circuit protection feature, the maximum output voltage under normal operation should be maintained belo w the minimum value specified, in order to prevent possible disturbance of the current control loop. (4) this is the time for which the device remains active after the en pin has been asserted low. this delay is necessary to all ow the output to be maintained during dc pwm mode operation. (5) the minimum pwm signal frequency during this mode of operation is to ensure that the device remains active during pwm contro l. this provides a continuous dc output current. for lower frequencies, the device will be gated 'on' and 'off' during pwm control. (6) the maximum pwm signal frequency during this mode of operation should be kept as low as possible to minimize errors due to t he turn-off delay of the device (see enable pin turn-off delay).
ZXLD1100 semiconductors issue 2 - february 2004 4 block diagram pin no. name description 1 lx output of ndmos switch 2 gnd ground (0v) 3 fb feedback pin for current control loop (connect resistor r1 from this pin to gnd for output current i=100mv/ r1) 4 en enable input (active high to turn on device) also used to adjust output current by pwm signal. connect to v in for permanent operation. 5 vsense output voltage sense (used for open circuit protection). connect to gnd if not required. 6v in input voltage (2.5v to 5.5v). decouple with capacitor close to device. pin description
device description the device is a pfm flyback dc-dc boost converter, working in discontinuous mode. with reference to the chip block diagram and typical application circuit, the operation of the device is as follows: control loop when 'en' is high, the control circuits become active and the low side of the coil (l1) is switched to ground via ndmos transistor (mn). the current in l1 is allowed to build up to an internally defined level (nominally 320ma) before mn is turned off. the energy stored in l1 is then transferred to the output capacitor (c2) via schottky diode (d1). when the voltage on c2 has risen above the threshold voltage of the series connected leds, current will flow through external sense resistor r1. the voltage developed across r1 is sensed at pin 'fb' and compared to a 100mv reference voltage (v ref ). a comparator senses when the feedback voltage is above v ref and its output is used to control the 'off' time of the output switch. the control loop is self-oscillating, producing pulses of up to 5 s maximum duration (switch 'on'), at a frequency that varies in proportion to the led current. the feedback loop maintains a voltage of v ref at the fb pin and therefore defines a maximum led current equal to v ref divided by r1. the minimum 'off' time of the output switch is fixed at 0.5ms nominal, to allow time for the coil's energy to be dissipated before the switch is turned on again. this maintains stable and efficient operation in discontinuous mode. open circuit protection there is an internal avalanche diode between the v sense and fb pins of the device. this diode, together with the associated resistors provides open circuit protection when the v sense pin is connected to the output voltage. in the event of an open circuit condition, the output voltage will rise above the breakdown voltage of the internal diode, which will then conduct and override the control signal from the current sense resistor. this maintains the output voltage at a level below the breakdown voltage of the output switch. supply current in this condition will fall to a low value as the control loop provides only the bias current for the diode. filtered pwm operation the input of an internal low pass filter is switched to v ref when the en pin is high and switched to ground when the en pin is low. the output of this filter drives the comparator within the control loop. a continuous high state on en therefore provides a filtered voltage of value v ref to the comparator. however, by varying the duty cycle of the en signal at a suitably high frequency (f>10khz), the control loop will see a voltage, that has an average value equal to the duty cycle multiplied by v ref . this provides a means of adjusting the output current to a lower value. it also allows the device to be both turned on and adjusted with a single signal at the 'en' pin. the output during this mode of operation will be a dc current equal to (v ref /r1) x duty cycle gated pwm operation the internal circuitry of the ZXLD1100 is turned off when no signal is present on the 'en' pin for more than 120 s (nominal). a low frequency signal applied to the en pin will therefore gate the device 'on' and 'off' at the gating frequency and the duty cycle of this signal can be varied to provide a 'chopped' output current equal to (v ref /r1) x duty cycle. for best accuracy, the gating frequency should be made as low as possible (e.g. below 1khz), such that the turn off delay of the chip is only a small proportion of the gating period further details of setting output current are given in the applications section under brightness control. ZXLD1100 semiconductors issue 2 - february 2004 5
ZXLD1100 semiconductors issue 2 - february 2004 6 typical characteristics (for typical application circuit at v in =3v and ta=25 c unless otherwise stated)
ZXLD1100 semiconductors issue 2 - february 2004 7 typical operating characteristics (for typical applications circuit at v in =3v, l=10 h coilcraft do1608c series, 3 series leds, i led =15ma, t a =25 c unless otherwise stated)
applications programming the maximum led current the maximum led current is programmed by adding a single resistor in series with the led chain. the current is determined by the resistor value and feedback voltage and is given by: i led = v fb /r1 where v fb =100mv the table below gives recommended resistor values for required led currents: led current r1 value 10ma 10 15ma 6.8 20ma 5 30ma 3.3 dimming control via a pwm signal on the en pin a pulse width modulated (pwm) signal can be applied to the en pin in order to adjust the output current to a value below the maximum led current. two modes of adjustment are possible as described below. true analog dimming - filtered ?dc? mode if a pwm signal of 10khz or higher is applied to the en pin, the device will remain active when the en pin is low. however, the input to the internal low pass filter will be switched alternately from v ref to ground, with a duty cycle (d) corresponding to that of the pwm signal. this will present a filtered dc voltage equal to the duty cycle multiplied by v ref to the control loop and will produce a dc output current lower than the maximum set value. this current is given by: i outdc = 0.1d/r1 this mode of adjustment minimizes flicker in the light output and system noise. pulsed dimming - gated mode if a lower frequency of 1khz or less is applied to the en pin, the device will be gated ?on? and ?off? at a duty cycle (d) corresponding to that of the input signal. the average output current is then given by: i outavg 0.1d/r1 this mode may be preferred over dc current control if the purest white output is required. however, note the 120 s nominal turn-off delay of the device, when using the device in this mode. dimming control using a dc voltage for applications where the en pin is not available a dc voltage can be used to control dimming. by adding resistors r2 and r3 and applying a dc voltage, the led current can be adjusted from 100% to 0%. as the dc voltage increases, the voltage drop across r2 increases and the voltage drop across r1 decreases, thus reducing the current through the leds. selection of r2 and r3 should ensure that the current from the dc voltage is much less than the led current and much larger than the feedback current. the component values in the diagram below represent 0% to 100% dimming control from a 0 to 2v dc voltage. dimming control using a logic signal for applications where the led current needs to be adjusted in discrete steps a logic signal can be applied as shown in the diagram below. when q1 os ?off?, r1 sets the minimum led current. when q1 is ?on?, r2 sets the led current that will be added to the minimum led current. the formula for selecting values for r1 and r2 are given below: mosfet ?off? i v r led min fb led () mosfet ?on? i v r i led max led led min fb () () where v fb = 100mv ZXLD1100 semiconductors issue 2 - february 2004 8
open circuit protection the voltage sense pin (v sense ) can be connected to the output to provide open circuit protection for the device and external circuits when driving series connected leds, thus eliminating the need for an external zener diode. protection is provided by the internal avalanche diode (zd), which limits the maximum output voltage to a value below the breakdown voltage of the output switch when the connection to the diodes is broken. capacitor selection a ceramic capacitor grounded close to the gnd pin of the package is recommended at the output of the device. surface mount types offer the best performance due to their lower inductance. a minimum value of 0.22 f is advised, although higher values will lower switching frequency and improve efficiency especially at lower load currents. a higher value will also minimize ripple when using the device to provide an adjustable dc output current. a good quality, low esr capacitor should also be used for input decoupling, as the esr of this capacitor is effectively in series with the source impedance and lowers overall efficiency. this capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. a minimum value of 1 f is acceptable if the input source is close to the device, but higher values will improve performance at lower input voltages, when the source impedance is high. the input capacitor should be mounted as close as possible to the ic for maximum stability over temperature, capacitors with x7r dielectric are recommended, as these have a much smaller temperature coefficient than other types. a table of recommended manufacturers is provided below: manufacturer website murata www.murata.com taiyo yuden www.t-yuden.com kemet www.kement.com avx www.avxcorp.com ZXLD1100 semiconductors issue 2 - february 2004 9
inductor selection the choice of inductor will depend on available board space as well as required performance. small value inductors have the advantage of smaller physical size and may offer lower series resistance and higher saturation current compared to larger values. a disadvantage of lower inductor values is that they result in higher frequency switching, which in turn causes reduced efficiency due to switch losses. higher inductor values can provide better performance at lower supply voltages. however, if the inductance is too high, the output power will be limited by the internal oscillator, which will prevent the coil current from reaching its peak value. this condition will arise whenever the ramp time (i lx(peak) x l/v in ) exceeds the nominal 5 s maximum ?on? time limit for the lx output. the graphs opposite show the ZXLD1100 performance for given inductor values and different manufacturers. recommended inductor values for the ZXLD1100 are in the range 6.8 hto22 h. the inductor should be mounted as close to the device as possible with low resistance connections to the lx and vin pins. suitable coils for use with the ZXLD1100 are shown in the table below: part no. l ( h) dcr ( ) i sat (a) manufacturer cmd4d11-100mc 10 0.457 0.5 sumida www.sumida.com do1608-103 10 0.16 1.1 coilcraft www.coilcraft.com lqh31cn100 10 1.3 0.23 murata www.murata.com lb2012y100mr 10 0.5 0.1 taiyo yuden www.t-yuden.com diode selection the rectifier diode (d1) should be a fast low capacitance schottky diode with low reverse leakage at the working voltage. it should also have a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. the table below gives some typical characteristics for diodes that can be used with the ZXLD1100: diode v f @ 100ma (mv) i fsm (ma) ic (ma) i r at 30v ( a) package zhcs400 300 1000 400 15 sod323 zhcs500 300 1000 500 15 sot23 layout considerations pcb tracks should be kept as short as possible to minimize ground bounce, and the ground pin of the device should be soldered directly to the ground plane. it is particularly important to mount the coil and the input/output capacitors close to the device to minimize parasitic resistance and inductance, which will degrade efficiency. the fb pin is a high impedance input so pcb track lengths to this should also be kept as short as possible to reduce noise pickup. excess capacitance from the fb pin to ground should be avoided. ZXLD1100 semiconductors issue 2 - february 2004 10
reference designs 3 led driver for handset lcd backlight ZXLD1100 semiconductors issue 2 - february 2004 11 circuit diagram performance graphs ref value package part number manufacturer notes u1 sc70-6 ZXLD1100h6 zetex led driver ic d1 400ma sod323 zhcs400 zetex 400ma schottky diode l1 10 h cmd4d11-100mc sumida 1mm height profile r1 6.8 0603 generic generic r2 1 100k 0603 generic generic c1 1 f 0603 generic generic c2 1 f 0603 generic generic leds nscw215 nichia 3pcs per board bill of materials note: r2 is optional. if en is floating add r2 to shutdown the ZXLD1100 and leds. if en pin can be driven low, r2 is not necessary. note: led current is set to 15ma
4 led driver for handset lcd backlight ZXLD1100 semiconductors issue 2 - february 2004 12 circuit diagram performance graphs ref value package part number manufacturer notes u1 sc70-6 ZXLD1100h6 zetex led driver ic d1 400ma sod323 zhcs400 zetex 400ma schottky diode l1 10 h cmd4d11-100mc sumida 1mm height profile r1 6.8 0603 generic generic r2 1 100k 0603 generic generic c1 1 f 0603 generic generic c2 1 f 0603 generic generic leds nscw215 nichia 4pcs per board bill of materials note: r2 is optional. if en is floating add r2 to shutdown the ZXLD1100 and leds. if en pin can be driven low, r2 is not necessary. note: led current is set to 15ma
5 led driver for handset main and sub display lcd backlight ZXLD1100 semiconductors issue 2 - february 2004 13 circuit diagram performance graphs ref value package part number manufacturer notes u1 sc70-6 ZXLD1100h6 zetex led driver ic d1 400ma sod323 zhcs400 zetex 400ma schottky diode l1 10 h cmd4d11-100mc sumida 1mm height profile r1 6.8 0603 generic generic r2 1 100k 0603 generic generic c1 1 f 0603 generic generic c2 1 f 0603 generic generic leds nscw215 nichia 5pcs per board bill of materials note: r2 is optional. if en is floating add r2 to shutdown the ZXLD1100 and leds. if en pin can be driven low, r2 is not necessary. note: led current is set to 15ma
6 led driver for lcd backlight ZXLD1100 semiconductors issue 2 - february 2004 14 circuit diagram performance graphs ref value package part number manufacturer notes u1 sc70-6 ZXLD1100h6 zetex led driver ic d1 400ma sod323 zhcs400 zetex 400ma schottky diode l1 10 h cmd4d11-100mc sumida 1mm height profile r1 6.8 0603 generic generic r2 1 100k 0603 generic generic c1 1 f 0603 generic generic c2 1 f 0603 generic generic leds nscw215 nichia 6pcs per board bill of materials note: r2 is optional. if en is floating add r2 to shutdown the ZXLD1100 and leds. if en pin can be driven low, r2 is not necessary. note: led current is set to 15ma
ZXLD1100 semiconductors issue 2 - february 2004 15 europe zetex plc fields new road chadderton oldham, ol9 8np united kingdom telephone (44) 161 622 4444 fax: (44) 161 622 4446 hq@zetex.com zetex gmbh streitfeldstra?e 19 d-81673 mnchen 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, ny 11788 usa telephone: (1) 631 360 2222 fax: (1) 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 2003 dim millimeters inches dim millimeters inches min max min max min max min max a 0.80 1.10 0.0315 0.0433 e 2.10bsc 0.0826 bsc a1 - 0.10 - 0.0039 e1 1.25 1.35 0.0492 0.0531 a2 0.80 1.00 0.0315 0.0394 e 0.65 bsc 0.0255 bsc b 0.15 0.30 0.006 0.0118 e1 1.30 bsc 0.0511 bsc c 0.08 0.25 0.0031 0.0098 l 0.26 0.46 0.0102 0.0181 d 2.00 bsc 0.0787 bsc a 0 8 0 8 package dimensions controlling dimensions are in millimeters. approximate conversions are given in inches package outline - sc70-6

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