white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 1 pt4103_ds rev en_2.2 pt4103 general description the pt4103 is a step-up dc/dc converter designed for driving up to 8 white leds in series from a single cell lithium ion battery with cons tant current. because it directly regulates output current, the pt4103 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. a single external resistor sets led current between 5ma and 20ma, which can then be eas ily 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. the pt4103 is available in sot23-6 packages. features z drives up to 5 series white leds from 2.5v z drives up to 8 series white leds from 3.6v z up to 87% efficiency z 1.2mhz fixed switching frequency z low 104mv feedback voltage z open load shutdown z soft start/pwm dimming z sot23-6 packages applications z cell phones z handheld computers and pdas z digital cameras z small lcd displays ordering information package temperature range ordering part number transport media marking sot23-6 -40 o c to 85 o c PT4103B23F tape and reel 3000 units 4103 typical applications key performance chart efficiency vs n(led) 4led 5led 6led 7led 8led 3led 75.00% 80.00% 85.00% 90.00% 510 15 20 25 iout (ma) vin=3.6v figure1. li-ion driver for six white leds figure2. efficiency vs number of leds
white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 2 pt4103_ds rev en_2.2 pt4103 pin assignment pin descriptions sot pin no. pin names description 1 sw power switch output. connect the inductor and the blocking schottky diode to sw. 2 gnd ground 3 fb feedback input pin. the reference voltage at this pin is 104mv. connect the cathode of the lowest led to fb and a current sense resistor between fb and gnd. 4 en enable pin. a high input at en enables the device and a low input disables the devices. when not used, connect en to the input source for automatic startup. 5 ov over voltage input. ov measures the output voltage for open circuit protection. connect ov to the output at the top of the led string. 6 in input supply pin. must be locally bypassed. absolute maximum ratings (note 1) symbol items value unit v in input voltage -0.3 6 v v sw voltage at sw pin -0.5 35 v v io all other i/o pins gnd-0.3 to vdd+0.3 v p tr1 thermal resistance sot-23-6 ja jc 220 110 /w tstg storage temperature -55 to 150 tsolder package lead soldering temperature 260 , 10s
white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 3 pt4103_ds rev en_2.2 pt4103 recommended operating range (note 2) symbol items value unit v in vin supply voltage 2.5 to +6 v v sw output voltage v in to 28 v t opt operating temperature -40 to +85 note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. note 2: recommended operating range indicates cond itions for which the device is functiona l, but does not guarantee specific performance limits. electrical characteristics (note 3,4,5) v in =v en =3v, topt=25 unless specified otherwise. symbol items conditions min. typ. max. unit v in input voltage 2.5 6 v feedback v fb fb pin voltage 89 104 119 mv ibias fb pin input bias current 0.05 1 a operating current ioff operating current shutdown v sw-on =0v 0.1 1 a isby operating current quiescent v fb =0.3v 100 350 a fsw switching frequency 1.0 1.25 1.5 mhz dmax maximum duty cycle v fb =0v 85 90 % chip enable v en_h en minimum high level 1.5 v v en_l en maximum low level 0.4 v v hys en hysteresis 90 mv en input bias current v sw-on =0v, 5v 1 a output switch 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 open circuit protection v ov open circuit shutdown threshold v ov rising 30 v soft start tss soft start time (note 3) v in power on 160 s note 3: electrical characteristics state dc and ac electrical specifications under particular test conditions which guarantee specific performance limits. this assumes that the device is within the recommended operating range. specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. note 4: typicals are measured at 25 ? c and represent the parametric norm. note 5: datasheet min/max specification lim its are guaranteed by design, test, or statistical analysis.
white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 4 pt4103_ds rev en_2.2 pt4103 simplified block diagram figure 3. simplified block diagram of the pt4103 operation description the pt4103 uses a constant frequency, peak current mode boost regulator architecture to regulate the series string of white leds. the operation of the pt4103 can be understood by referring to the simplified block diagram shown above. at the start of each oscillator cycle, the control logic turns on the power switch m1. the signal at the non-inverting input of the pwm comparator is proportional to the switch current, summed together with a portion of the oscillator ramp. when this signal reaches the level set by the output of error amplifier, the pwm comp arator resets the latch in the control logic and turns off the power switch. 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 resu lts in more current to flow through m1, hence increasin g the power delivered to the output. typical performance characteristics driving capability vin i led =15ma i led =20ma 2.5v 5 x led 4 x led 3.0v 6 x led 5 x led 3.6v 8 x led 8 x led efficiency vs vin and i led efficiency vs temperature efficiency vs. temperature 10ma 15ma 20ma 80.00% 81.00% 82.00% 83.00% 84.00% 85.00% 86.00% 87.00% 88.00% 89.00% 90.00% -50 0 50 100 150 temp (c) efficiency efficiency vs. vin 5ma 10ma 15ma 20ma 70.00% 75.00% 80.00% 85.00% 90.00% 95.00% 100.00% 3 3.13.23.3 3.43.53.63.73.83.9 4 4.14.24.3 4.44.5 vin (v)
white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 5 pt4103_ds rev en_2.2 pt4103 typical performance characteristics quiescent current vs v in and temperature iq vs temperature 0 50 100 150 200 250 2.5 3 3.5 4 4.5 5 5.5 6 vin(v) iq(ua) temp=-40 temp=25 temp=100 switching frequency vs temperature fosc vs temp. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 -40 25 100 temp() fosc(mhz) application information ? inductor selections for most of the applications of the pt4103, it is recommended to use an inductor of 22uh. although 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 tab le 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 pt4103 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 pt4103 applications. ? diodes selection schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for pt4103 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 capacitance 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 pt4103. a schottky diode rated at 100ma to 200ma is sufficient for most pt4103 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 control the led current is controlled by the feedback resistor. the feedback reference is 104mv. the led current is 104mv/rfb. in order to have accurate led current, precision resistors are preferred (1% is recommended). the formula and table for r fb selection are shown below: r fb = 104mv/i led i led ma r fb value ? 5 20.8 10 10.4 15 6.93 20 5.2
white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 6 pt4103_ds rev en_2.2 pt4103 ? open circuit protection open circuit protection will shut off the pt4103 if the output voltage 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 pt4103 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 pt4103 checks this condition and if the output ever exceeds 30v, the pt4103will sh ut 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 3. as the dc voltage increases, the voltage drop on r2 increases and the voltage drop on r1 decreases. thus, the led current decreases. the selection of r2 and r3 will make the current from the variable dc source much smaller than the led current and much larger than the fb pin bias current. 2. using a pwm signal to en pin with the pwm signal applied to the en pin, the pt4103 is turned on or off by the pwm signal. the leds operate at either zero or full current. the average led current increases propo rtionally with the duty cycle of the pwm signal. a 0% duty cycle will turn off the pt4103 and corresponds to zero led current. a 100% duty cycle correspo nds to full current. the typical frequency range of the pwm signal should be 1khz or less due to the soft start function. 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 5. ? start-up and inrush current the pt4103has internal soft start to limit the amount of current through vin at startup and to also limit the amount of overshoot on the output. 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. ? board layout consideration as with all switching regulators, careful attention must be paid to the pcb board layout and component placement. to maximize effici ency, switch rise and fall times are made as short as possible. to prevent electromagnetic interference (emi) problems, proper layout of the high frequency switching path is essential. the voltage signal of the sw pin has sharp rise and fall edges. minimize the length and area of all traces connected to the sw pin and always use a ground plane under the switching regulator to minimize interplane coupling. in addition, the ground connection for the feedback resistor r1 should be tied directly to the gnd pin and not shared with any other component, ensuring a clean, noise-free connection. figure3. dimming control using a dc voltage figure4. dimming control using a pwm signal figure5. dimming control using a filtered pwm signal
white led step-up converter china resources powtech (shanghai) limited www.crpowtech.com page 7 pt4103_ds rev en_2.2 pt4103 package information sot23-6 millimeters inches symbol min max min max a 1.050 1.250 0.041 0.049 a1 0.000 0.100 0.000 0.004 a2 1.050 1.150 0.041 0.045 b 0.300 0.400 0.012 0.016 c 0.100 0.200 0.004 0.008 d 2.820 3.020 0.111 0.119 e 1.500 1.700 0.059 0.067 e1 2.650 2.950 0.104 0.116 e 0.950typ 0.037typ e1 1.800 2.000 0.071 0.079 l 0.700ref 0.028ref l1 0.300 0.600 0.012 0.024 0 8 0 8 d b e1 e e e1 a a2 a1 l c l1 0.2
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