revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 1 description the SE3362 is a charge pump operating in either 1x mode or 2x fractional mode regulating current through each of the 4 led pins. operation at a fixed high frequency of 1mhz typical allows the use of very small value ceramic capacitors. the SE3362 drives white light-emitting diodes (led?s) connected in parallel and provides tightly matched regulated current to achieve uniformity of brightness in lcd backlighting applications. an external resistor rset controls the output current level. led currents of up to 30ma are supported over a range of input supply voltages from 2.85v to 5.5v, making the device ideal for battery-powered applications. led dimming can be accomplished by several methods including using a resistor rset (the exact formula will be provided in the application section) to set the rset pin current, applying a pwm signal on the control signals, or adding a switched resistor in parallel with rset. the enable input pin allows the device to be placed in power-down mode with close to "zero? quiescent current. the SE3362 features short circuit and over temperature protection (otp). the device is available in a 16- lead thin qfn package with a max height of 0.8mm. features ? drives individually up to 4 leds ? output current up to 30ma per led ? digital control on/off of each led ? compatible with supply voltage of 2.85v to 5.5v ? power efficiency up to 90% ? 2 modes of operation 1x and 2x ? automatic short circuit detect/disable ? high-frequency operation at 1mhz ? low value ceramic capacitors ? automatically switch to power save mode if no led is deteted to be connected to the ic ? thin qfn 16-lead package, 33mm ? 100% lead (pb)-free application diagram application ? color lcd and keypad backlighting ? cellular phones ? handheld devices ? digital cameras ? pdas ? portable mp3 players
revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 2 pin configuration note: the package exposed pad is electrica lly connected inside the package to agnd. functional pin description pin number name function 1 en chip enable (active high). note that this pin is high impedance. there should be a pull low 100k resistor connected to gnd when the control signal is floating. 2 ctr0 output control bit 0. (see table 1) 3 ctr1 output control bit 1. (see table 1) 4 agnd analog ground 5 rset led current is set by the value of the resistor r set connected from the rset pin to ground. do not short the rset pin. v iset is typically 1.1v. all ex ternal capacitance at this pin, including board parasitic capacit ance, must be less than or equal to 30pf. 6 vout output voltage source for connection to the led anodes. 7 vin input voltage 8 c1+ positive terminal of bucket capacitor 1 9 c1- negative terminal of bucket capacitor 1 10 nc no connection 11 nc no connection 12 pgnd power ground. this ground should be connected to power gnd on pcb. 13 to16 led 4 to 1 current sink for led. (if not in use, pin should be connected to v out ) exposed pad gnd exposed pad should be soldered to pcb board and connected to gnd.
revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 3 absolute maximum rating (1) parameter value units vin, vout, ledx voltage -0.3 7v v en, ctrx,rset voltage -0.3 to vin v rset current 1 ma lead temperature (soldering, 5 sec.) 260 c junction temperature 0 to +150 c storage temperature -40 to +150 c operating rating (2) parameter symbol value units supply input voltage range v in 5.5 v junction temperature range t j 0 to +125 c i led per led pin 0to 30 ma electrical characteristics vin = 3.5v; c1 1.0 f ; t j = 25c; unless otherwise noted parameter symbol conditions min typ max unit input supply voltage v in 2.85 -- 5.5 v rset regulated voltage v rset 1.22 1.25 1.28 v current into leds i led r set =100k -- 5 -- ma r set =25.0 k -- 20 -- ma r set =16.7 k -- 30 -- ma en=low, shutdown mode -- 1 -- ua 1x mode , no load -- 170 -- ua quiescent current i q 2x mode, no load -- 2.5 -- ma i led accuracy i led-err 2ma revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 4 note 1: exceeding the absolute maximum rating may damage the device. note 2: the device is not guaranteed to f unction outside its operating rating. note 3: current matching refers to the differenc e in current from on led to the next. iled current matching = % 100 ) ( ) ( ) ( ) ( + ? min led max led min led max led i i i i control inputs output status ctrl1 ctrl0 led4 led3 led2 led1 0 0 off off on on 0 1 off on on on 1 0 on on on on table1 1 1 off off off off operations the SE3362 is a high efficiency charge pump white led driver. it provides 4 channels low drop-out voltage current source to regulated 4 white led?s current. for high efficiency, the SE3362 implements x1/x2 mode charge pump. an external r set is used to set the current of white led. dimming control ctrl0 and ctrl1 are used to control the on/off of white led. when an external pwm signal is connected to the control pin, brightness of white led is adjusted by the duty cycle. the SE3362 supports the dimming control frequency up to 1khz. led current setting the current of white led connected to SE3362 can be set by r set . the channel current that flows through the white led is 400 times greater than the current of r set . the white led can be estimated by following equation: iled = 400 ? ? ? ? ? ? ? ? set rset r v where v rset = 1.25v, and r set is the resistance connected from rset to gnd. thermal shutdown the SE3362 provides a high current capability to drive 4 white leds. a thermal shutdown circuit is needed to protect the chip from thermal damage. when the chip reaches the shutdown temperature 150 c, the thermal shutdown circuit turns off the chip to prevent the thermal accumulation in the chip. short circuit protection the SE3362 provides short circuit protection function. when output voltage is shorted to gnd, short circuit protection cell shutdown chargepump and current source, and consequently the ic and the related led?s are protected.
revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 5 applications information selecting capacitors to get the better performance of SE3362, the selecting o f peripherally appropriate capacitor and value is very important. these capacitors determine some parameters such as input and output ripple, power efficiency, maximum supply current by charge pump, and start-up time. to reduce the input and output ripple effectively, the low esr ceramic capacitors are recommended. generally, to reduce the output ripple, in creasing the output capacitance c out is necessary. however, this will increase the start-up time of output voltage. for led driving applications, the input voltage ripple is more important than output ripple. input ripple is controlled by input capacitor c in , increasing the value of input capacitance can further reduce the ripple. practically, the input voltage ripple depends on the power supply?s impedance. if a single input capacitor c in cannot satisfy the requirement of application, it is necessary to add a low-pa ss filter as show s in figure 1. figure1. c-r-c filter used to reduce input ripple the flying capacitor c1 determines the supply current capability of the c harge pump and to influence the overall efficiency of system. the lower value will improve efficiency, but it will limit the led ? s current at low input voltage. setting the led current the SE3362 can be set a fixed le d?s current by a resiste r r set connected from rset to gnd. r set establishes the reference current and mirrors the current into led1, led2, led3, and led4. the current into led is about 400 times of the current flows through the rset, the appro ximate setting formula is given as follows: i led (a) = ) ( ) ( 500 set r v led current and table 2 shows the values of r set for a fixed led current. i led (ma) r set (k ) 5 100 10 50 15 33.3 20 25.0 25 20 table 2 30 16.7 led current setting with nmos led current setting control can also be achieved by using the external nmos to change equivalent resister of rset pin. figure 2 shows this application circuit of method. for this example, a 3 bit signals can set 8 kinds of different equivalent resister of rset pin, i.e. produce 8 kinds of led current level. table 3 shows the relation between equivalent resister of rset pin and control signal. figure 2. the application circuit of setting led current which using a nmos to set r set .
revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 6 table 3. the relation between control signal and equivalent resister of rset pin s1 s2 s3 equivalent resister of rset pin ( r set ) 0 0 0 r set = r 4 0 0 1 r set = r 3 //r 4 0 1 0 r set = r 2 //r 4 0 1 1 r set = r 2 //r 3 //r 4 1 0 0 r set = r 1 //r 4 1 0 1 r set = r 1 //r 3 //r 4 1 1 0 r set = r 1 //r 2 //r 4 1 1 1 r set = r 1 //r 2 //r 3 //r 4 led dimming control methods the SE3362 can use two methods to achieve the led dimming control. these methods are detailed described as following: (1) dimming using pwm signal into ctrl0 and ctrl1 led current can be controlled by applying a pwm signal to ctrl0 or ctrl1. table 1 shows the relationship between ctrlx and 4 led's current states. for an example, as the ctrl1 is pulled logical high and ctrl0 receives a pwm signal, then, four led?s will be dimmed synchronously. here, the pwm signal setting the led's current on/off can achieve the average led's current which in design. the application circuit is shown in figure 3. figure 4, and figure 5 show 3wleds and 2wl eds pwm dimming application circuit, respectively. during the time of pwm signal logical low, the current is a fixed value and setting by r set resistor. so the average leds current can be approximated as equation. i led(avg) = pwm on led off t i t ) ( where: t pwm is the period of pwm dimming signal t off is the time of pwm signal at low. i led(on) is led on state current. figure 3. the pwm dimming application circuit for 4wleds figure 4. the pwm dimming application circuit for 3wleds figure 5. the pwm dimming application circuit for 2wleds additionally, SE3362 has 100us delay time between mode transfer. this delay time makes different dimming frequency corresponds to different maximum duty of ctrlx pin. please note that the maximum dimming frequency can not exceed the maximum dimming frequency which is internally set at 1khz.
revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 7 the following equation shows the relation between maximum duty of ctrlx pin and pwm dimming frequency. table 4 is shown the common dimming frequency and its corresponding maximum duty. for better performance consideration, the maximum pwm dimming frequency is recommended below 1khz. d (max) = (1-100 10 -6 f d ) table 4. the common dimming frequency and its corresponding maximum duty. dimming frequency (hz) ctrlx maximum duty rled minimum duty 1000 0.90 0.10 900 0.91 0.09 800 0.92 0.08 700 0.93 0.07 600 0.94 0.06 500 0.95 0.05 400 0.96 0.04 300 0.97 0.03 200 0.98 0.02 (2). the pwm dimming by gpio the pwm dimming by gpio is shown as figure 6. dz shall be a schottky diode with forward voltage less than 0.3v at i f = 1ma. c3 is a capacitor to keep the enable pin voltage is higher than the threshold voltage. r1 is discharge resister and it should be not too high to prevent the off time too long while turned-off. the recommended conditions are shown as following. 1. the recommended value for r1 and c3 are 200k ( 5%) and 0.22 f (x7r, 10%). 2. the forward voltage of the schottky diode shall be less than 0.3v at 1ma. 3. the output voltage of gpio should be greater than 2.8v and keep the voltage on en pin is higher than 1.5v. 4. the pwm frequency should be in the range of 500hz~1.5khz or 20khz~30khz for audio noise consideration. 5. the pwm duty cycle shall be in the range of 30% to 95%. 6. the driving capability of the gpio should be greater than 2ma @ 2.8v. 7. the led current can be obtained by the equation, i led = 400 ) 1 ( pwm set rset d r v ? (the typical value of v rset is 1.25v) figure 6. the gpio pwm dimming application circuit
revision 12/4/2008 preliminary and all contents are subject to change without prior notice ? seaward electronics, inc., 2007. ? www.seawardinc.com.cn ? page 8 customer support seaward electronics incorporated ? china section b, 2nd floor, shangdi scientific office complex, #22 xinxi road haidian district, beijing 100085, china tel: 86-10-8289-5700/01/05 fax: 86-10-8289-5706 seaward electronics corporation ? taiwan 2f, #181, sec. 3, minquan east rd, ta i p e i , ta i w a n r . o . c tel: 886-2-2712-0307 fax: 886-2-2712-0191 seaward electronics incorporated ? north america 1512 centre pointe dr. milpitas, ca95035, usa tel: 1-408-821-6600 last updated - 12/4/2008 outline drawing for qfn16 3x3
|
