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white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 1 PT1505_ds rev en_1.1 PT1505 general description the PT1505 is an integrated power management unit and white led driver for small handheld portable applications. it contains a single-cell lithium ion battery charger, a synchronous step-down dc-dc converter, 2 low dropout regulators and a step-up dc-dc converter designed for driving up to 8 white leds in series. it allows charging from both wall adapter and usb port. when charging from wall adapter, the PT1505 increases the charging current automatically. the battery charger is a highly integrated charging management device targeted at space limited portable applications. it offers an integrated mosfet and current sensor, reverse blocking protection, high accuracy current and voltage regulation, and charge termination. it charges a battery in three phases: trickle charging, constant current and constant voltage. no external sense resistor is needed, and no blocking diode is required due to the in ternal mosfet architecture. the thermal feedback regulates the charging current to limit the chip temperature during high power operation or high ambient temperature to maximize the charge rate without risk of overheating. the charge voltage is fixed at 4.2v, and the charge current can be programmed externally with a single resistor. the pt1502 automatically terminat es the charge cycle when the charge current drops to 1/10 the programmed value after the final float voltage is reached. the pt1502 automatically re-starts the charge if the battery voltage falls below an internal threshold. the step-down converter is a high efficiency monolithic current mode synchronous buck regulator with a constant operation frequency. a main switch and a synchronous switch are integrated in pt1502, the device has high efficiency and no external schottky diode needed. 100% duty cycle provides low dropout operation, extending battery life in portable systems. automatic burst mode operation at light loads provides high efficiency. internal 1.5mhz switching frequency allowing the use of small surface mounts inductors and capacitors. the output voltage can be adjusted by external resistors. the two low-dropout voltage regulators are designed for portable and wireless applications. it can provide better than 60db psrr at 1khz. the output current can be up to 300ma. one regulator?s output voltage is fixed at 3.0v, and the other one is adjusted to 2.5v, 2.8v, 3.0v, 3.3v by two control pins. the white led step-up dc-dc converter is ideal for driving light emitting diodes (leds) whose light intensity is proportional to the current passing through them, not the voltage across their terminals, as it directly regulates output current a single external resistor sets led current between 5ma and 20ma, which can then be easily adjusted using either a dc voltage or a pulse width modulated (pwm) signal. its low 104mv feedback voltage reduces power loss and improves efficiency. the ov pin monitors the output voltage and turns off the converter if an over-voltage condition is present due to an open circuit condition. features z integrated switch for usb/ac adapter supply z 220ua quiescent supply current(includes step-down dc-dc converters , two low dropout regulators and step-up dc-dc converter) z integrated single-cell lithium ion battery charger ? auto thermal regulated ? charging current up to 800ma ? charging current adjusted by external resistor z integrated step-dow n dc-dc converter ? output voltage adjusted by external resistor ? output current up to 600ma ? 1.5m hz fixed switching frequency ? over-current and over-temperature protection z integrated two low dropout regulators ? ldo1: output voltage 3.0v up to 300ma output current ? ldo2: output voltage optional for 2.5v/2.8v/3.0v/3.3v up to 300ma output current ? psrr: 60db@1k hz ? over-current and over-temperature protection z integrated white led step-up dc-dc converter ? drives up to 8 series white leds ? up to 87% efficiency ? 1.25mhz fixed switching frequency ? low 104mv feedback voltage ? open load shutdown ? soft start/pwm dimming z qfn28 5x5 package z rohs compliant free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 2 PT1505_ds rev en_1.1 PT1505 applications z mp3/4 z pdas z gsm/cdma mobile phone z portable media players z digital cameras z small lcd displays ordering information package temperature range ordering part number transport media marking qfn28 -40 o c to 85 o c PT1505eqfn tape and reel PT1505 xxxxxx note: typical application circuit figure1. typical application circuit 1 of PT1505 (mcu controls en1 pin) xxxxxx assembly factory code lot number free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 3 PT1505_ds rev en_1.1 PT1505 enable control boost dc- dc 1 1 1 100k pgnd gnda en up _ reset pwr _ hold 100k pvdd1 to battery 1uf l1=22uh sw1 ov led1 led6 led5 led4 led3 led2 fb 1 0. 22uf 5.2 ? r3 figure2. typical application circuit 2 of PT1505 (up_reset controls en1 pin) pin assignment free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 4 PT1505_ds rev en_1.1 PT1505 pin description pin no. pin names pin description 1 ov over voltage input for led step-up dc-dc converter. 2 sw1 switch port for led step-up dc-dc converter 3 pgnd1 power ground for led step-up dc-dc converter 4 ldoout2 ldo2 output 5 ldo2_set1 ldo2 output voltage setting bit msb 6 gnda3 analog ground 7 play_on system start up signal for battery 8 pwr_hold feedback chip enabled signal from cpu 9 gnda2 analog ground for step-down dc-dc converter 10 fb2 feedback port for st ep-down dc-dc converter 11 bat_low battery voltage lower than 3.3v signal 12 up_reset cpu reset signal 13 pvdd2 supply port for step-down dc-dc converter 14 sw2 switch port for step-down dc-dc converter 15 pgnd2 power ground for step-down dc-dc converter 16 usb_in usb supply 17 ac_in indicator for ac adapter connected 18 chgin ac adapter input 19 chg_stat charging state indicator 20 bat battery input 21 ldoout1 ldo1 output 22 chg_prog charging current setting pin, connects resistor to gnda3 23 avdd analog supply 24 ldo2_set0 ldo2 output voltage setting bit lsb 25 pvdd1 supply port for led step-up dc-dc converter 26 en1 enable pin for led step-up dc-dc converter 27 gnda1 analog ground for led step-up dc-dc converter 28 fb1 feedback port for le d step-up dc-dc converter free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 5 PT1505_ds rev en_1.1 PT1505 absoloute maximum rating (note1) symbol items value unit v in input supply voltage: usb_in chgin avdd pvdd1,pvdd2 ? 0.3 ~ 6 v v io input/output signal: play_on pwr_hold up_reset bat_low ldo2_set0 ldo2_set1 buckfb ldo1out ldo2out chg_prog sw2, en1, ac_in ? 0.3 ~ v in v vsw1 voltage at sw1 pin -0.5 35 v t j junction temperature -40~125 c t stg storage temperature range ? 65 ~ 150 c t solder lead temperature (soldering, 10 sec) 260 c recommended operating range (note2) symbol items value unit v in input supply voltage: usb_in chgin 4.25 ~ 5.5 v v in2 input supply voltage: avdd pvdd1, pvdd2 3.5 ~ 5.5 v t oper operating temperature range ? 40 ~ 85 c ja thermal resister 50 c/w note1: absolute maximum ratings are those values beyond which the life of the device maybe impaired. note2: recommended operating range indicates conditions for which the device is functional, but does not guarantee specific performance limits. electrical characteristics v bat =3.6v t a =25 , unless otherwise specified symbol parameter conditions min typ max units i q bat supply quiescent current chgin/usb_in floating boost/buck/ldo1/ldo2 no load 220 650 a i shdn bat supply shut down current chgin/usb_in floating play_on=gnda3, pwr_hold=gnda3 1.2 6 a v il maximum low input level at play_on, pwr_hold avdd = 3.0 to 5.5v 0.4 v v ih minimum high input level at play_on, pwr_hold avdd = 3.0 to 5.5v 1.5 v v lbat battery voltage undervoltage lockout threshold vbat high to low 3.135 3.3 3.465 v t lbat battery voltage undervoltage lockout comparator filter time 1 ms v lbathys battery voltage undervoltage lockout hysteresis 100 mv free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 6 PT1505_ds rev en_1.1 PT1505 electrical characteristics (continued) symbol parameter conditions min typ max units tsd thermal shutdown temperature 160 c thermal shutdown hysteresis 20 c charger characteristics symbol parameter conditions min typ max units v chg input charging supply voltage 4.25 5.5 v v bat_reg regulated output voltage i ch_cc = 50ma, r prog =5k 4.158 4.2 4.242 v r prog =1k, usb mode 445 470 495 ma i ch_cc const current mode charging current r prog =1k, adapter mode 750 ma i trikl trickle charge current v bat < v trikl i ch_cc /10 ma v trikl trickle charge threshold voltage v bat from low to high 2.9 v v trhys trickle charge hysteresis voltage 80 mv v uv under voltage lockout threshold v chgin from high to low 3.8 v v uvhys under voltage lockout hysteresis 200 mv i term charging termination current ich_cc/10 ma v prog chg_prog pin voltage const current mode 1.0 v v rechg recharge battery threshold voltage vbat_reg - vchg 150 mv t lim junction temperature in constant temperature mode 120 t rechg recharge comparator filter time vbat from high to low 2 ms i prog prog pin pull-up current 3 a dc-dc step down conv erter characteristics symbol parameter conditions min typ max units v fb regulated feedback voltage 0.588 0.600 0.612 v ? v out line regulation pvdd = 3.5v to 5.5v 0.04 0.4 %/v i limit peak induct or current 1 a v loadreg load regulation 0.5 % f osc oscillator frequency 1.2 1.5 1.8 mhz r pfet rds(on) of p-channel fet i lx = 100ma 0.4 0.8 ? free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 7 PT1505_ds rev en_1.1 PT1505 electrical characteristics (continued) symbol parameter conditions min typ max units r nfet rds(on) of n-channel fet i lx = ?100ma 0.35 0.7 ? led dc-dc step up converter characteristics symbol parameter conditions min typ max units v en1_h en1 minimum high level 1.5 v v en1_l en1 maximum low level 0.4 v v en1hys en1 hysteresis 90 mv en1 input bias current v sw-on =0v, 5v 1 a v fb fb pin voltage 89 104 119 mv fsw switching frequency 1.0 1.25 1.5 mhz d max maximum duty cycle v fb =0v 85 90 % r on sw on resistance (note 3) 0.5 ? i limit sw current limit 400 ma i leak sw leakage current vsw 5v 0.01 1 a v ov open circuit shutdown threshold v ov rising 30 v tss soft start time (note 1) v in power on 160 s low dropout regulator characteristics symbol parameter conditions min typ max units v ldo1 output voltage 1 2.94 3.0 3.06 v ldo2_set0=low, ldo2_set1=low 2.45 2.5 2.55 ldo2_set0=high, ldo2_set1=low 2.744 2.8 2.856 ldo2_set0=low, ldo2_set1=high 2.94 3.0 3.06 v ldo2 output voltage 2 ldo2_set0=high, ldo2_set1=high 3.234 3.3 3.366 v line regulation error av d d = ( v ldo(nom) + 0.5v) to 5.5v 0.1 0.5 %/v vout load regulation error i ldo_out = 1ma to 150 ma 15 50 mv i outmax peak output current v ldo v ldo(nom) ? 2% 300 ma free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 8 PT1505_ds rev en_1.1 PT1505 electrical characteristics (continued) symbol parameter conditions min typ max units i out = 50ma 60 f=1k hz i out = 150ma 60 i out = 50ma 55 psrr power supply rejection ratio av d d =v ldo(nom) +1.0v f=10khz i out = 150ma 55 db i ldo_out = 50ma 50 90 mv v diff dropout voltage i ldo_out = 100ma 100 180 mv i sc output short current limit output grounded 500 ma v ldo_out / v out v out temperature characteristics temperature = -40 to 125c 100 ppm/c simplified block diagram figure3. simplified block diagram of PT1505 free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 9 PT1505_ds rev en_1.1 PT1505 operation description power up sequency: the up_reset signal will reset the cpu. and the pwr_hold contains the pmu in normal working status. when the play_on button is hold up to high level for several hundred milliseconds pmu will be ready to start. first, to start the buck , then delay 40 milliseconds, to start the ldo, and after 80 milliseconds, the up_reset turns on to high level. start up sequence by external button power down description when button the play_on in working status, this action will be checked by cpu and it shuts up inner blocks and sends low level to pwr_hold. when the play_on is loosened the play_on becomes low, and pmu will power down. bat low voltage detection when in working status, the voltage of bat pin lowers than 3.3v, then pt1502 puts the bat_low pin to high level. this signal will be sent to cpu. adapter and usb plug in when usb or adapter is plugged in, the pt1502 would detect whether the supply is higher than 3.8v. if the supply voltage is lower than 3.8v, the charger stops to charge. and if the battery voltage is lower than 2.9v, pmu doesn?t start up. and it will charge the battery until it over the 2.9v. when the battery is absent, the pt1502 will stabilize the bat pin voltage to 4.2v. sequence of plugging in the usb or adapter free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 10 PT1505_ds rev en_1.1 PT1505 battery charger the pt1502 includes a linear li-ion battery charger with thermal regulation. with the internal 0.6 ohms mosfet, the minimum charging supply voltage can be less than 4.25v. one external 1% precision resistor is required to set the charging current value. when the voltage at the chgin pin rises above the uvlo threshold, the normal charging cycle begins. if the battery voltage is less than 2.9v, the device will operate in a trickle charging mode. the charging current in the trickle charging mode is 1/10 th of the programmed value, which effectively protects the battery from damage and prolongs its lifetime. when the voltage at the bat pin rises above 2.9v, the charger enters the constant-current mode in which case the charging current equals to the programmed value. once the voltage at the bat pin reaches 4.2v, the charger goes into the constant voltage mode where the charging current decreases. once the charging current drops to 1/10 th the programmed value, the charging cycle ends. after a charge cycle is complete and the charging operation is terminated, the pt1502 keeps monitoring the bat voltage. it will recharge the battery as soon as the bat voltage drops below 4.05v. the pt1502 includes a soft-start circuit to minimize the inrush current at the start of a ch arge cycle. when the prog pin is floating, the charger goes into the shutdown mode. buck the pt1502 includes a high efficiency current mode synchronous buck regulator with a constant operation frequency. its internal integrated mosfets achieve high efficiency. ultra low output voltages are easily available with the 0.6v feedback reference voltage. internal fixed 1.5mhz switching frequency allowing the use of small surface moun t inductors and capacitors. the 2.7v to 5.5v input voltage range and 600ma output current make the buck ideally suited for single li-ion battery-powered applications. current mode pwm control loop slope compensated current mode pwm control and cycle-by-cycle current limit provides stable operation and excellent line and load regulation. during normal operation, the internal top power mosfet is turned on each cycle when the rising e dge of the oscillator sets the rs latch, and turned off when rising edge of the pwm comparator resets the rs latch. while the top mosfet is off, the bottom mosfet is turned on until either the inductor current starts to reverse or the beginning of the next clock cycle. the internal comparator controls output transient overshoots is smaller than 8% by turning the main mosfet off until the fault is removed. skip-cycles mode operation at light loads, the buck enters skip-cycle mode automatically. in this mode, the inductor current may reach zero or reverse on each cycle. the pwm control loop will automatically skip cycles to maintain output regulation. the bottom mosfet is turned off by the current reversal comparator, and the switch voltage will ring. this is discontinuous mode operation, and is normal behavior for the switching regulator. low-dropout operation when the input voltage deceases to the value of output voltage, the control loop remains the main mosfet on until it reaches 100% duty cycle. the output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperatur e of the ic because the rdson of the main mosfet increases and the efficiency of the converter decrease. ldo the block of voltage reference provides the reference voltage of the ldo. the op-amp block is used as the error amplifier of the ldo by comparing the reference with the output feedback voltages. its output controls the gate of a large pmos pass element and hereby adjusts the output voltage. the current limit block senses the ldo output current free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 11 PT1505_ds rev en_1.1 PT1505 and limits the output current from being too high. this is mostly a short circuit protection feature. white led step-up converter it is a constant frequency, peak current mode boost regulator to regulate the series string of white leds. after power up on the pvdd1 pin, if the voltage at en1 pin reaches more than 1.5v, this converter will starting to work. at the start of each oscillator cycle, control logic turns on a power switch. the signal at the non-inverting input of the pwm comparator is proportional to the switch current, summed together with a portion of an oscillator ramp. when this signal reaches the level set by the out put of error amplifier, the pwm comparator resets the latch in the control logic and turns off the power swit ch. in this manner, error amplifier sets the correct peak current level to keep the led current in regulation. if the feedback voltage starts to drop, the output of the error amplifier increases. this result in more current to flow through power switch, hence increasing the power delivered to the output. the converter?s driving capability is listed as follows: pvdd1 i led =15ma i led =20ma 3.0v 6 x led 5 x led 3.6v 8 x led 8 x led application information battery charger adjusting charging current the charging current is programmed using 1% precision resistor from prog pin to ground. when usb supply the PT1505, the charging current and the programming resistor are calculated using the following equations: r prog =470v/i chg , i chg =470v/r prog when adapter alone or both adapter and usb supply the PT1505, the charging cu rrent and the programming resistor are calculated using the following equations: r prog =750v/i chg , i chg =750v/r prog thermal limiting an internal thermal fee dback loop reduces the programmed charge curren t if the die temperature attempts to rise above a preset value of approximately 120 . this feature protects the PT1505 from excessive temperature and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the PT1505. the conditions that cause the PT1505 to reduce charge current through thermal feed back can be approximated by considering the power diss ipated in the ic. nearly all of this power dissipation is generated by the internal mosfet?this is calculated to be approximately: pd = (v chgin ? v bat ) ? i bat where pd is the power dissipated v chgin is the input supply voltage v bat is the battery voltage i bat is the charge current. the approximate ambient te mperature at which the thermal feedback begins to protect the ic is: t a = 120 ? pd? ja t a = 120 ? (v chgin ? v bat ) ? i bat ? ja reducing the voltage drop across the internal mosfet can significantly decrease th e power dissipation in the ic. this has the effect of increasing the current delivered to the battery during thermal regulation. one method is by dissipating some of the power through an external component, such as a resistor or diode. by dropping voltage across a resistor in series with a 5v wall adapter, the on-chip power dissipation can be decreased, thus increasing the thermally regulated charge current. under voltage lockout (uvlo) an internal under voltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until chgin rises above the under voltage lockout threshold. the uvlo circuit has a built-in hysteresis of 200mv. furthermore, to prot ect against reverse current in the power mosfet, the uvlo circuit keeps the charger in shutdown mode if chgin falls to within 30mv of the battery voltage. if the uvlo comparator is tripped, the charger will not come out of shutdown mode until v chgin rises 100mv above the battery voltage. stability considerations the constant-voltage mode feedback loop is stable free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 12 PT1505_ds rev en_1.1 PT1505 without an output capacitor provided a battery is connected to the charger output. with no battery present, an output capacito r is recommended to reduce ripple voltage. in constant current mode, the prog pin is in the feedback loop, not the battery. the constant-current mode stability is affected by the impedance at the prog pin. with no additional capacitance on the prog pin, the charger is stable with the programming resistor value as high as 20k. however, additional capacitance on this node reduces the maximum allowed program resistor. the pole frequency at the prog pin should be kept above 100khz. buck setting the output voltage the output voltage is set by an external resister divider according to the following formula: ? ? ? ? ? ? + = 1 2 1 6 . 0 r r v v out inductor selection for most applications, the PT1505 operates well with inductors of 1uh to 4.7uh. low inductance values are physically smaller but requi re fast switching, which results in efficiency loss. the inductor value can be calculated from following equation: osc l in out in out f i v v v v l ? = ) ( table 1 list some typical surface mount inductors that adapt to PT1505 applications input and output capacitor selection the input capacitor reduces the surge current drawn from the input and switching noise from the device. to prevent large voltage transients, a low esr input capacitor sized for the maxi mum rms current must be used. the maximum rms capacitor current is given by: [ ] in out in out omax rms v v v v i i 2 1 ) ( ? ceramic capacitor with x5r or c7r dielectrics are highly recommended because of their low esr and small temperature coefficients. a 4.7uf ceramic capacitor for most applications is sufficient. the output capacitor is required to obtain small output voltage ripple and ensure regulation loop stability. typically, once the esr requirement for cout has been met, the rms current generally far exceeds the ripple current requirement. the output ripple v out is determined by: ) 8 1 ( out l out fc esr i v + where f is the operating frequency, cout is the output capacitor and i l is the ripple current of inductor current. ceramic capacitors with x5 r or c7r dielectrics are recommended due to their low esr and high current rating. a 10uf ceramic capac itor for most applications is recommended for low output voltage ripple and good loop stability. ldo input capacitor an input capacitor of 1.0 f is required between the avdd and gnd pin. this capacitor must be located within 1cm distance from avdd pin and connected to a clear ground. a ceramic capacitor is recommended although a good quality tantalum or film may be used at the input. however, a tantalum capacitor can suffer catastrophic failures due to surge current when connected to a low impedance power supply (such as a battery or a very large capacitor). there is no requirement for the esr on the input capacitor, but the tolerance and temperature coefficient must be considered in order to ensure the capacitor work within the operation range over the full range of temperature and operating conditions. output capacitor in applications, it is important to select the output capacitor to keep the PT1505 in stable operation. the output capacitor must meet all the requirements specified in the following recommended capacitor table table 1. typical surface mount inductors free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 13 PT1505_ds rev en_1.1 PT1505 over all conditions in applications. the minimum capacitance for stability and correct operation is 0.6 f. the capacitance tolerance should be 30% or better over the operation temperature range. the recommended capacitor type is x7r to meet the full device temperature specification. recommended output capacitor (c out ) typ min max unit capacitance 1.0 0.6 10 f esr 0 400 m the capacitor application conditions also include dc-bias, frequency and temperature. unstable operation will result if the capacitance drops below minimum specified value. the ldo is designed to work with very small ceramic output capacitors. a 1.0 f capacitor (x7r type) with esr type between 0 and 400m is suitable in the pt1502 applications. x5r capacitors may be used but have a narrow temperature range. with these and other capacitor types (y5v, z6u) that may be used, selection relies on the range of operating conditions and temperature range for a specified application. it may also be possible to use tantalum or film capacitors at the output, but these are not as good for reasons of size and cost. it is also recommended that the output capacitor be located within 1cm from the output pin and return to a clean ground wire. no-load stability the ldo will remain stable and in regulation with no external load. this is especially important in cmos ram keep-alive applications. ldo output voltage setting ldo2_set0 ldo2_set1 ldo2out low low 2.5v high low 2.8v low high 3.0v high high 3.3v the table of voltage of ldo2 setting the voltage of ldo1is fixed at 3.0v the voltage of ldo2 can be adjusted to 2.5v 2.8v 3.0v 3.3v by setting ldo2_set0 and ldo2_set1. white led step-up converter inductor selection for most of the applications of white led step-up converter subsystem of PT1505, it is recommended to use an inductor of 22uh. a lthough small size is one of the major factors in selecting an inductor, the smaller and thinner inductors give higher core losses at 1.25mhz and drc, resulting in lower efficiencies. the following table provides a list of recommended inductors: part number dcr ? current rating ma manufacture lqh3c220 0.71 250 murata cdrh3d16-220 0.53 350 sumida lb2012b220m 1.7 75 taiyo yuden lem2520-220 5.5 125 taiyo yuden ejpc220kf 4.0 160 panasonic capacitor selection the small size of ceramic capacitors makes them ideal for the white led step-up converter subsystem of PT1505 applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as y5v or z5u. a 1 f input capacitor and a 0.22 f output capacitor are sufficient for most PT1505 applications. diode selection schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for the white led step-up converter subsystem of PT1505 applications. the forward voltage drop of a schottky diode represents the conduction losses in the diode, while the diode capacitance (c t or c d ) represents the switching losses. for diode selection, both forward voltage drop and diode cap acitance need to be considered. schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.25mhz switching frequency of the white led step-up converter subsystem of PT1505. a schottky diode rated at 100ma to 200ma is free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 14 PT1505_ds rev en_1.1 PT1505 sufficient for most white led step-up converter subsystem of PT1505 applications. some recommended schottky diodes are listed in the following table: part number forward current (ma) voltage drop (v) diode cap (pf) manu facture cmdsh-3 100 0.58@100ma 7.0@10v central cmdsh2-3 200 0.49@200ma 15@10v central bat54 200 0.53@100ma 10@25v zetex led current contro l the led current is controlled by the feedback resistor. the feedback reference is 104mv. the led current is 104mv/r3 in order to ha ve accurate led current, precision resistors are preferred (1% is recommended). the formula and table for r 3 selection are shown below: r 3 = 104mv/i led i led ma r 3 value ? 5 20.8 10 10.4 15 6.93 20 5.2 open circuit protection open circuit protection will shut off the white led step-up converter subsystem of PT1505 if the voltage at the ov pin goes too high when the ov pin is tied to the output. in some cases an led may fail, which will result in the feedback voltage always being zero. the white led step-up converter subsystem will then switch at its maximum duty cycle boosting the output voltage higher and higher. by connecting the ov pin to the top of the led string the white led step-up converter subsystem of PT1505 checks this condition and if the output ever exceeds 30v, the white led step-up converter subsystem of PT1505 will shut down. the part will not switch again until the power is recycled. dimming control there are three different types of dimming control circuits: 1. using a dc voltage for some applications, the preferred method of brightness control is a variable dc voltage to adjust the led current. the dimming control using a dc voltage is shown in figure 4. as the dc voltage increases, the voltage drop on r4 increases and the voltage drop on r3 decreases. thus, the led current decreases. the selection of r4 and r5 will make the current from the variable dc source much smaller than the led current and much larger than the fb pin bias current. PT1505 fb1 led1 led3 led2 v dc r5 5k ? r4 5.2 ? r3 figure4. dimming control using a dc voltage 2. using a pwm signal to en pin with the pwm signal applied to the en1 pin, the white led step-up converter subsystem of PT1505 is turned on or off by the pwm signal. the leds operate at either zero or full current. the average led current increases proportionally with the duty cycle of the pwm signal. a 0% duty cycle will turn off the white led step-up converter subsystem of PT1505 and corresponds to zero led current. a 100% duty cycle corresponds to full current. the typical frequency range of the pwm signal should be 1 khz or less due to the soft start function. fb1 led1 led3 led2 en1 r6 pwm PT1505 100k r6 5.2 ? r3 figure5. dimming control using a pwm signal 3. using a filtered pwm signal the filtered pwm signal can be considered as an adjustable dc voltage. it can be used to replace the variable dc voltage source in dimming control. the circuit is shown in figure 6. free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 15 PT1505_ds rev en_1.1 PT1505 figure6. dimming control using a filtered pwm signal start-up and inrush current the white led step-up converter subsystem of PT1505 has internal soft start to limit the amount of current through pvdd1 pin at startup and to also limit the amount of overshoot on the sw1 pin. the soft start is realized by gradually increasing the current limit during start-up. the current limit is increased by a third every 60 s giving a total soft start time of around 180 s. en1 control however, other than dimming applications, we recommend two methods con cerning to controlling the white leds driver subsystem enable signal, that is the en1 pin. one method is to use a microcontroller unit (mcu) to control this pin (figure 1), the other is connecting the en1 pin to the up_reset pin (figure 2) to let the pmu subsystem powered up firstly (when the pmu subsystem powered up completely, the up_reset signal will become logic high, see later) and then utilize the up_reset signal to enable the white led driver subsystem. it will ensure the PT1505 operate more swimmingly using above two methods. layout guideline when laying out the pc board, the following layout guideline should be followed to ensure proper operation of the PT1505: 1. the power traces, includ ing gnd traces, the sw1, sw2 traces and the pvdd1, pvdd2 trace should be kept short, direct and wide to allow large current flow. the l1, l2 connection to the corresponding sw1, sw2 pins should be as short as possible. use several via pads when routing between layers. 2. the input capacitors should be connected as close as possible to chgin and pgnd to get good power filtering. 3. keep the switching nod e sw1, sw2 away from the corresponding sensitive fb1, fb2 node. 4. the feedback trace for the buck should be separate from any power trace and connected as closely as possible to the load point. sensing along a high current load trace will degrade dc load regulation. 5. sw1, sw2 and the corresponding output capacitors should be connected as close as possible and there should not be any signal lines under the inductor. 6. the resistance of the trace fr om the load return to the pgnd2 should be kept to a minimum. this will help to minimize any error in dc re gulation due to differences in the potential of the internal signal ground and the power ground. free datasheet http:///
white led driver & pmu for portable applications china resources powtech (shanghai) limited www.crpowtech.com page 16 PT1505_ds rev en_1.1 PT1505 package information qfn28(5*5) millimeter symbol min nom max a 0.70 0.75 0.80 a1 - 0.01 0.05 b 0.18 0.25 0.30 c 0.18 0.20 0.25 d 4.90 5.00 5.10 d2 3.50ref e 0.50bsc ne 3.00bsc nd 3.00bsc e 4.90 5.00 5.10 e2 3.50ref l 0.35 0.40 0.45 h 0.30 0.35 0.40 l/f ? mil 150*150 free datasheet http:///

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