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ltc3217 1 3217f features descriptio u multi-led camera light supply for cellphones/ dscs/pdas charge pump provides high efficiency with automatic mode switching multimode operation: 1x, 1.5x, 2x four low dropout led outputs up to 600ma total output current independent torch and flash i set and enable pins low noise constant frequency operation* pwm brightness control via the en2 pin low shutdown current: 4 a internal soft-start limits inrush current during start-up and mode switching open/short led protection no inductors (3mm x 3mm) 16-lead qfn plastic package 600ma low noise multi-led camera light charge pump the ltc 3217 is a low noise charge pump dc/dc con- verter designed to power four high current leds. the ltc3217 requires only four small ceramic capacitors and two current set resistors to form a complete led power supply and current controller. built-in soft-start circuitry prevents excessive inrush cur- rent during start-up and mode changes. high switching frequency enables the use of small external capacitors. independent high and low current settings are programmed by two external resistors. shutdown mode and current output levels are selected via two logic inputs. the current through the leds is programmed via i set1 and i set2 . in addition, the brightness can be controlled by pulse width modulation of the en2 pin. the charge pump optimizes efficiency based on the volt- age across the led current sources. the part powers up in 1x mode and will automatically switch to boost mode whenever any enabled led current source begins to enter dropout. the first dropout switches the part into 1.5x mode and a subsequent dropout switches the part into 2x mode. the ltc3217 resets to 1x mode whenever the part is shut down. the ltc3217 is available in a low profile 16-lead (3mm 3mm 0.75mm) qfn package. typical applicatio u applicatio s u c2 2.2 f c3 2.2 f c1 2.2 f v bat 19.6k 1% 6.49k 1% led1 led2 led3 led4 gnd v bat en2 en1 ltc3217 c1p c1m c2p c2m c4 2.2 f aot-2015hpw-1751b 3217 ta01 i set1 i set2 cpo en1 (torch) en2 (flash) en1 0 1 0 1 0 (shutdown) 25ma/led 75ma/led 100ma/led en2 i led 0 0 1 1 , ltc and lt are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. *protected by u.s. patents, including 6411531 efficiency vs v bat v bat (v) 3 0 efficiency (p led /pin) (%) 10 30 40 50 100 70 3.4 3.8 4 3217 g09 20 80 90 60 3.2 3.6 4.2 4.4 total output current p led /pin led = 2015 hpw aot 100ma 200ma 400ma
ltc3217 2 3217f v bat , cpo to gnd ....................................... 0.3v to 6v en1, en2 .................................... 0.3v to (v bat + 0.3v) i cpo (note 2) ....................................................... 600ma i iled1-4 (note 3) .................................................. 150ma cpo short-circuit duration ............................. indefinite operating temperature range (note 4) ...40 c to 85 c storage temperature range ..................65 c to 125 c order part number t jmax = 125 c, ja = 68 c/w exposed pad (pin 17) is gnd must be soldered to pcb ltc3217eud absolute axi u rati gs w ww u package/order i for atio uu w (note 1) consult ltc marketing for parts specified with wider operating temperature ranges. qfn part marking lbtq 16 15 14 13 5 6 7 8 top view 17 ud package 16-lead (3mm 3mm) plastic qfn 9 10 11 12 4 3 2 1 c1p cpo en1 led1 c2m en2 i set2 i set1 c2p v bat c1m gnd1 led2 led3 led4 gnd2 electrical characteristics the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v bat = 3.6v, c1 = c2 = c3 = c4 = 2.2 f, unless otherwise noted. order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbf lead free part marking: http://www.linear.com/leadfree/ parameter conditions min typ max units v bat operating voltage 2.9 4.5 v i vbat operating current r iset1 = r iset2 = 20k, en1 = en2 = high i cpo = 0ma, 1x mode 1 ma i cpo = 0ma, 1.5x mode 4 ma i cpo = 0ma, 2x mode 6 ma v bat shutdown current 4 a led 1-4 current led current ratio (i led /i set1/2 )i led = 25ma to 100ma 370 400 430 ma/ma led dropout voltage mode switch threshold, i led = 100ma 330 mv mode switching delay en1 only 2.5 ms led current matching any two outputs, i led = 100ma 1 % charge pump (cpo) 1x mode output voltage i cpo = 0ma v bat v 1.5x mode output voltage i cpo = 0ma 4.5 v 2x mode output voltage i cpo = 0ma 5.05 v 1x mode output impedance 0.5 ? 1.5x mode output impedance v bat = 3.4v, v cpo 4.6v (note 5) 2.8 ? 2x mode output impedance v bat = 3.2v, v cpo 5.1v (note 5) 3.2 ? clock frequency 0.6 0.85 1.15 mhz
ltc3217 3 3217f electrical characteristics typical perfor a ce characteristics uw the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v bat = 3.6v, c1 = c2 = c3 = c4 = 2.2 f, unless otherwise noted. note 1: absolute maximum ratings are those values beyond which the life of a device may become impaired. note 2: based on charge pump long-term current density limitations. assumes an operating duty cycle of 10% under absolute maximum conditions for durations less than 10 seconds. maximum current for continuous operation is 300ma. note 3: based on led current source long-term current density limitations. assumes an operating duty cycle of 10% under absolute maximum conditions for durations less than 10 seconds. maximum current for continuous operation is 100ma. note 4: the ltc3217e is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the 40 c to 85 c ambient operating temperature range are assured by design, characterization and correlation with statistical process controls. note 5: 1.5x mode output impedance is defined as (1.5v bat ?v cpo )/i out . 2x mode output impedance is defined as (2v bat ?v cpo )/i out . led dropout voltage vs led current led current (ma) 10 0 led dropout voltage (mv) 100 200 300 400 20 30 40 50 3217 g01 60 70 80 90 100 v bat = 3.6v led pin voltage (v) 0 0 led pin current (ma) 20 40 60 80 100 120 0.2 0.4 0.6 0.8 3217 g02 1.0 v bat = 3.6v r iset (k ? ) 0 i led (ma) 40 80 120 20 60 100 10 20 30 40 3217 g03 50 5 015253545 led pin current vs led pin voltage i led vs r iset parameter conditions min typ max units en1, en2 low level input voltage (v il ) 0.4 v high level input voltage (v ih ) 1.4 v input current (i ih ) 730 a input current (i il ) ? 1 a minimum pwm on-time en2 only 50 s maximum pwm off-time en2 to remain enabled, en1 = low 1ms i set1 , i set2 v iset1 , iset2 i led1-4 = 12.5ma 1.175 1.215 1.255 v i iset1 , iset2 current range 31.25 375 a i iset1 , iset2 short-circuit current 800 a t a = 25 c unless otherwise noted.
ltc3217 4 3217f v bat shutdown current vs v bat voltage oscillator frequency vs supply voltage efficiency vs v bat v bat voltage (v) 2.9 1.5 v bat shutdown current ( a) 2.5 3.5 4.5 5.5 3.3 3.7 4.1 4.5 3217 g07 6.5 7.5 3.1 3.5 3.9 4.3 t a = 85 c t a = 25 c t a = ?0 c v bat supply voltage (v) 2.9 880 frequency (khz) 890 910 920 930 980 950 3.3 3.7 3.9 3217 g08 900 960 970 940 3.1 3.5 4.1 4.3 4.5 t a = ?0 c t a = 25 c t a = 85 c v bat (v) 3 0 efficiency (p led /pin) (%) 10 30 40 50 100 70 3.4 3.8 4 3217 g09 20 80 90 60 3.2 3.6 4.2 4.4 total output current p led /pin led = 2015 hpw aot 100ma 200ma 400ma 1.5x mode cpo output ripple 2x mode cpo output ripple charge pump mode switching and input current to ground (400ma load) v cpo 50mv/div ac coupled 500ns/div v bat = 3.6v i cpo = 400ma c cpo = 2.2 f 3217 g10 v cpo 20mv/div ac coupled 500ns/div 3217 g11 v bat = 3.6v i cpo = 400ma c cpo = 2.2 f v cpo 1v/div i vbat 500ma/div 0 en1 5v/div 1ms/div 1x no load 1x dropout dropout 1.5x 2x (5v) v in = 3.6v 3217 g12 1x mode switch resistance vs temperature 1.5x mode charge pump open-loop output resistance vs temperature (1.5v bat ?v cpo )/i cpo temperature ( c) ?0 0.35 switch resistance ( ? ) 0.40 0.45 0.50 0.55 0.60 0.65 ?5 10 35 60 3217 g04 85 i cpo = 200ma v bat = 3.3v v bat = 3.9v v bat = 3.6v temperature ( c) ?0 2.0 switch resistance ( ? ) 2.2 2.4 2.6 2.8 3.0 3.2 ?5 10 35 60 3217 g05 85 v bat = 3v v cpo = 4.2v c2 = c3 = c4 = 2.2 f 2x mode charge pump open-loop output resistance vs temperature (2v bat ?v cpo )/i cpo temperature ( c) ?0 2.6 switch resistance ( ? ) 2.8 3.0 3.2 3.4 3.6 3.8 ?5 10 35 60 3217 g06 85 v bat = 3v v cpo = 4.8v c2 = c3 = c4 = 2.2 f typical perfor a ce characteristics uw t a = 25 c unless otherwise noted.
ltc3217 5 3217f uu u pi fu ctio s 1.5x mode cpo voltage vs load current load current (ma) 3.6 cpo voltage (v) 4.0 4.4 4.8 3.8 4.2 4.6 100 200 300 400 3217 g13 500 0 c2 = c3 = c4 = 2.2 f v bat = 3v 3.2v 3.3v 3.6v 3.1v 3.5v 3.4v 2x mode cpo voltage vs load current load current (ma) 0 cpo voltage (v) 4.8 5.0 5.2 400 3217 g14 4.6 4.4 4.7 4.9 5.1 4.5 4.3 4.2 100 200 300 500 c2 = c3 = c4 = 2.2 f v bat = 3v 3.1v 3.2v 3.3v 3.6v c1p, c2p, c1m, c2m (pins 1, 16, 14, 12): charge pump flying capacitor pins. a 2.2 f x7r or x5r ceramic capaci- tor should be connected from c1p to c1m and c2p to c2m. cpo (pin 2): output of the charge pump used to power all leds. this pin is enabled or disabled using the en1 and en2 inputs. a 2.2 f x5r or x7r ceramic capacitor should be connected to ground. en1, en2 (pins 3, 11): inputs. the en1 and en2 pins are used to select which current level is being supplied to the leds, as well as to put the part into shutdown mode. the truth table for these pins is as follows: truth table en1 en2 mode 0 0 shutdown 1 0 low current 0 1 high current 1 1 low + high current en2 can be used for pwm of the led currents. for proper operation, the minimum pulse width should be 50 s and the maximum low time should be 1ms if en1 is low. if en1 is high then the 1ms low time limitation does not apply. led1, led2, led3, led4 (pins 4, 5, 6, 7): led1 to led4 are the current source outputs. each led is connected in between cpo (anodes) and led1 ?4 (cathodes). the current to each led output is set via the en1 and en2 inputs, and the programming resistors connected from i set1 and i set2 to gnd. any of the four led outputs can be disabled by connecting the output directly to cpo. 10 a of current will flow through each directly connected led output. for single led applications, all four led pins may be tied together and will accurately share current. gnd2 (pin 8): analog ground. this pin should be connected directly to a low impedance ground plane. i set1 /i set2 (pins 9, 10): led current programming resistor pins. the i set1 and i set2 pins will servo to 1.22v. resistors connected between each of these pins and gnd are used to set the high and low led current levels. connecting a resistor 2k or less will cause the ltc3217 to enter over-current shutdown. gnd1 (pin 13): charge pump ground. this pin should be connected directly to a low impedance ground plane. v bat (pin 15): supply voltage. this pin should be bypassed with a 2.2 f, or greater low esr ceramic capacitor. exposed pad (pin 17): this pad should be connected directly to a low impedance ground plane for optimal thermal and electrical performance. typical perfor a ce characteristics uw t a = 25 c unless otherwise noted.
ltc3217 6 3217f block diagra w en2 en1 control logic 850khz oscillator pwm timing thermal shutdown led current sources charge pump enable cp 4 0.8v i set2 1.22v mux i set1 v bat gnd2 led4 led3 led2 led1 cpo short-circuit protection cpo gnd1 c1p c1m c2p c2m 3217 bd + + 1 15 9 10 3 11 14 16 12 13 2 4 5 6 7 8 250k 250k + + operatio u power management the ltc3217 uses a switched capacitor charge pump to boost cpo to as much as 2 times the input voltage up to 5.1v. the part starts up in 1x mode. in this mode, v bat is connected directly to cpo. this mode provides maximum efficiency and minimum noise. the ltc3217 will remain in 1x mode until an led current source drops out. dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. when dropout is detected, the ltc3217 will switch into 1.5x mode. the cpo voltage will then start to increase and will attempt to reach 1.5x v bat up to 4.5v. any subsequent dropout will cause the part to enter the 2x mode. the cpo voltage will attempt to reach 2x v bat up to 5.05v. the ltc3217 will be reset to 1x mode whenever the part is shut down. a two phase non-overlapping clock activates the charge pump switches. in the 2x mode the flying capacitors are charged on alternate clock phases from v bat to minimize input current ripple and cpo voltage ripple. in 1.5x mode the flying capacitors are charged in series during the first clock phase and stacked in parallel on v bat during the second phase. this sequence of charging and discharging the flying capacitors continues at a constant frequency of 850khz.
ltc3217 7 3217f operatio u table 1. charge pump output regulation voltages charge pump mode regulated v cpo 1.5x 4.5v 2x 5.05v the led currents are delivered by the four programmable current sources. three discrete current settings (low, high, low + high) are available and may be selected via the en1 and en2 pins. the values of these currents may be selected by choosing the appropriate programming resistors. each re- sistor is connected between the i set1 or i set2 pin to ground. the resistor values required to attain the desired current levels can be determined by equation 1. r i set ledx 12 488 / = (1) an r setx resistor value of 2k or less (i.e., short-circuit) will cause the ltc3217 to enter overcurrent shutdown mode. this mode prevents damage to the part and external leds by shutting down the high power sections of the part. each led output can be disabled by connecting the pin directly to cpo. do not leave pins open as this will cause dropout and subsequently mode changing. pulse width modulation option en2 can be pulse width modulated to control the led brightness. the minimum allowable pulse width is 50 s and the maximum low time is 1ms. pulse width modulating the en2 input can be performed with en1 high or low. if en1 is high then there is no limitation on the en2 low time. when en1 is low the part would normally go into shutdown whenever en2 goes low. prevention of shutdown in this case is achieved by an internal timer which delays shutdown until en2 has remained low for at least 1ms. soft-start initially, when the part is in shutdown, a weak switch con- nects v bat to cpo. this allows v bat to slowly charge the cpo output capacitor and prevent large charging currents to occur. the ltc3217 also employs a soft-start feature on its charge pump to prevent excessive inrush current and supply droop when switching into the step-up modes. the current available to the cpo pin is increased linearly over a typical period of 125 s. soft-start occurs at the start of both 1.5x and 2x mode changes. charge pump strength and regulation regulation is achieved by sensing the voltage at the cpo pin and modulating the charge pump strength based on the error signal. the cpo regulation voltages are set internally, and are dependent on the charge pump modes as shown in table 1. when the ltc3217 operates in either 1.5x mode or 2x mode, the charge pump can be modeled as a thevenin-equivalent circuit to determine the amount of current available from the effective input voltage and effective open-loop output resis- tance, r ol (figure 1). r ol is dependent on a number of factors including the switching term, 1/(2f osc ? c fly ), internal switch resis- tances and the non-overlap period of the switching circuit. however, for a given r ol , the amount of current available will be directly proportional to the advantage voltage of 1.5v bat ?v cpo for 1.5x mode and 2v bat ?v cpo for 2x mode. consider the example of driving white leds from a 3.1v supply. if the led forward voltage is 3.8v and the current sources require 100mv, the advantage voltage for 1.5x mode is 3.1v ? 1.5 - 3.8v ?0.1v or 750mv. notice that if the input voltage is raised to 3.2v, the advantage voltage jumps to 900mv? 20% improvement in avail- able strength. from figure 1, for 1.5x mode the available current is given by: i vv r out bat cpo ol = 15 . (2) for 2x mode, the available current is given by: i vv r out bat cpo ol = 2 (3) notice that the advantage voltage in this case is 3.1v ? 2 ?3.8v ?0.1v = 2.3v. r ol is higher in 2x mode but a significant overall increase in available current is achieved.
ltc3217 8 3217f operatio u figure 1. equivalent open-loop circuit v cpo in calculating equations 2 and 3 is the minimum required voltage for the led and not the regulated voltage. typical values of r ol as a function of temperature are shown in figures 2 and 3. shutdown current in shutdown mode all the circuitry is turned off and the ltc3217 draws a very low current from the v bat supply. furthermore, cpo is weakly connected to v bat . the ltc3217 enters shutdown mode when both the en1 and en2 pins are brought low. en1 and en2 have 250k pull- down resistors to ground. thermal protection the ltc3217 has built-in overtemperature protection. at internal die temperatures of around 150 c thermal shut- down will occur. this will disable all of the current sources and charge pump until the die has cooled by about 15 c. this thermal cycling will continue until the fault has been corrected. cpo short-circuit protection the ltc3217 has internal cpo short-circuit protection. an internal comparator senses when cpo is below 0.8v which forces the part into shutdown. a pull-up device ensures start-up. mode switching the ltc3217 will automatically switch from 1x mode to 1.5x mode and subsequently to 2x mode whenever a dropout condition is detected at an led pin. dropout occurs when a current source voltage becomes too low for the programmed current to be supplied. the time from dropout detection and mode switching is about 2.5ms. this delay allows for the led to warm up and reduce its forward voltage which may remove the dropout condition. if pwm is used on the en2 pin, then the dropout time is dependent on one to two pwm clock pulses. the part is reset back to 1x mode when the part is shut down (en1 = en2 = low). the part may be set to the desired output current level via en1 and en2. an internal comparator will not allow the main switches to connect v bat and cpo in 1x mode until the voltage at the cpo pin has decayed to less than or equal to the voltage at the v bat pin. cpo 1.5v bat or 2v bat r ol 3217 f01 + + temperature ( c) ?0 2.0 switch resistance ( ? ) 2.2 2.4 2.6 2.8 3.0 3.2 ?5 10 35 60 3217 g05 85 v bat = 3v v cpo = 4.2v c2 = c3 = c4 = 2.2 f figure 2. 1.5x mode charge pump open-loop output resistance vs temperature (1.5v bat ?v cpo )/i cpo temperature ( c) ?0 2.6 switch resistance ( ? ) 2.8 3.0 3.2 3.4 3.6 3.8 ?5 10 35 60 3217 g06 85 v bat = 3v v cpo = 4.8v c2 = c3 = c4 = 2.2 f figure 3. 2x mode charge pump open-loop output resistance vs temperature (2v bat ?v cpo )/i cpo
ltc3217 9 3217f figure 4. 10nh inductor used for input noise reduction (approximately 1cm of board trace) v bat , cpo capacitor selection the style and value of the capacitors used with the ltc3217 determine several important parameters such as regulator control loop stability, output ripple, charge pump strength and minimum start-up time. to reduce noise and ripple, it is recommended that low equivalent series resistance (esr) ceramic capacitors are used for both cv bat and c cpo . tantalum and aluminum capacitors are not recommended due to high esr. the value of c cpo directly controls the amount of output ripple for a given load current. increasing the size of c cpo will reduce output ripple at the expense of higher start-up current. the peak-to-peak output ripple of the 1.5x mode is approximately given by the expression: i i fc ripplep out osc cpo -p = () 3 (4) where f osc is the ltc3217 oscillator frequency or typi- cally 850khz and c cpo is the output storage capacitor. the output ripple in 2x mode is very small due to the fact that load current is supplied on both cycles of the clock. both style and value of the output capacitor can significantly affect the stability of the ltc3217. as shown in the block diagram, the ltc3217 uses a control loop to adjust the strength of the charge pump to match the required output current. the error signal of the loop is stored directly on the output capacitor. the output capacitor also serves as the dominant pole for the control loop. to prevent ringing or instability, it is important for the output capacitor to maintain at least 1 f of capacitance over all conditions. in addition, excessive output capacitor esr will tend to degrade the loop stability. the esr of the output capacitor should be <100m ? . multilayer ceramic chip capacitors typically have exceptional esr performance. mlccs com- bined with a tight board layout will result in very good stability. as the value of c cpo controls the amount of output ripple, the value of cv bat controls the amount of ripple present at the input pin (v bat ). the ltc3217 input 3217 f04 ltc3217 v bat gnd current will be relatively constant while the charge pump is either in the input charging phase or the output charging phase but will drop to zero during the clock non-overlap times. since the non-overlap time is small (~25ns), these missing ?otches?will result in only a small perturbation on the input power supply line. note that a higher esr capacitor such as tantalum will have higher input noise due to the higher esr. therefore, ceramic capacitors are recommended for low esr. input noise can be further reduced by powering the ltc3217 through a very small series inductor as shown in figure 4. a 10nh inductor will reject the fast current notches, thereby presenting a nearly constant current load to the input power supply. for economy, the 10nh inductor can be fabricated on the pc board with about 1cm (0.4") of pc board trace. applicatio s i for atio wu uu flying capacitor selection warning: polarized capacitors such as tantalum or aluminum should never be used for the flying capacitors since their voltage can reverse upon start-up of the ltc3217. ceramic capacitors should always be used for the flying capacitors. the flying capacitors control the strength of the charge pump. in order to achieve the rated output current it is necessary to have at least 1.6 f of capacitance for each of the flying capacitors. capacitors of different materials lose their capacitance with higher temperature and volt- age at different rates. for example, a ceramic capacitor made of x7r material will retain most of its capacitance from ?0 c to 85 c whereas a z5u or y5v style capacitor will lose considerable capacitance over that range. z5u
ltc3217 10 3217f and y5v capacitors may also have a very poor voltage coefficient causing them to lose 60% or more of their capacitance when the rated voltage is applied. therefore, when comparing different capacitors, it is often more appropriate to compare the amount of achievable capaci- tance for a given case size rather than comparing the specified capacitance value. for example, over rated voltage and temperature conditions, a 1 f, 10v, y5v ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22 f, 10v, x7r available in the same case. the capacitor manufacturer? data sheet should be consulted to determine what value of capacitor is needed to ensure minimum capacitances at all temperatures and voltages. table 2 shows a list of ceramic capacitor manufacturers and how to contact them: table 2. recommended capacitor vendors avx www.avxcorp.com kemet www.kemet.com murata www.murata.com taiyo yuden www.t-yuden.com vishay www.vishay.com layout considerations and noise due to its high switching frequency and the transient currents produced by the ltc3217, careful board layout is necessary. a true ground plane and short connections to all capacitors will improve performance and ensure proper regulation under all conditions. the flying capacitor pins c1p, c2p, c1m and c2m will have very high edge rate waveforms. the large dv/dt on these pins can couple energy capacitively to adjacent pcb runs. magnetic fields can also be generated if the flying capacitors are not close to the ltc3217 (i.e., the loop area is large). to decouple capacitive energy transfer, a faraday shield may be used. this is a grounded pcb trace between the sensitive node and the ltc3217 pins. for a high quality ac ground, it should be returned to a solid ground plane that extends all the way to the ltc3217. the following guidelines should be followed when design- ing a pcb layout for the ltc3217: 1. the exposed pad should be soldered to a large copper plane that is connected to a solid, low impedance ground plane using plated through-hole vias for proper heat sinking and noise protection. 2. input and output capacitors must be placed close to the part. 3. the flying capacitors must be placed close to the part. the traces from the pins to the capacitor pad should be as wide as possible. 4. v bat , cpo traces must be wide to minimize inductance and handle high currents. 5. led pads must be large and connected to other layers of metal to ensure proper led heat sinking. power efficiency to calculate the power efficiency ( ) of a white led driver chip, the led power should be compared to the input power. the difference between these two numbers repre- sents lost power whether it is in the charge pump or the current sources. stated mathematically, the power efficiency is given by: = p p led in (5) the efficiency of the ltc3217 depends upon the mode in which it is operating. recall that the ltc3217 operates as a pass switch, connecting v bat to cpo, until dropout is detected at the led pin. this feature provides the opti- mum efficiency available for a given input voltage and led forward voltage. when it is operating as a switch, the efficiency is approximated by: == = p p vi vi v v led in led led bat bat led bat () () (6) since the input current will be very close to the sum of the led currents. applicatio s i for atio wu uu
ltc3217 11 3217f information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. at moderate to high output power, the quiescent current of the ltc3217 is negligible and the expression shown in equation 6 is valid. once dropout is detected at the led pin, the ltc3217 enables the charge pump in 1.5x mode. in 1.5x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 1.5 times the actual input voltage. this is because the input current for a 1.5x charge pump is approximately 1.5 times the load current. in an ideal 1.5x charge pump, the power efficiency would be given by: ideal led in led led bat led led bat p p vi vi v v == = () ((.))(.? 15 15 (7) similarly, in 2x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 2 times the actual input voltage. in an ideal 2x charge pump, the power efficiency would be given by: ideal led in led led bat led led bat p p vi vi v v == = () (())(? 22 (8) thermal management for higher input voltages and maximum output current, there can be substantial power dissipation in the ltc3217. if the junction temperature increases above approxi- mately 150 c the thermal shutdown circuitry will auto- matically deactivate the output current sources and charge pump. to reduce maximum junction temperature, a good thermal connection to the pc board is recommended. connecting the exposed pad to a ground plane and maintaining a solid ground plane under the device will reduce the thermal resistance of the package and pc board considerably. applicatio s i for atio wu uu package descriptio u ud package 16-lead plastic qfn (3mm 3mm) (reference ltc dwg # 05-08-1691) 3.00 0.10 (4 sides) note: 1. drawing conforms to jedec package outline mo-220 variation (weed-2) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 bottom view?xposed pad 1.45 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.25 0.05 1 pin 1 notch r = 0.20 typ or 0.25 45 chamfer 15 16 2 0.50 bsc 0.200 ref 0.00 ?0.05 (ud16) qfn 0904 recommended solder pad pitch and dimensions 1.45 0.05 (4 sides) 2.10 0.05 3.50 0.05 0.70 0.05 0.25 0.05 0.50 bsc package outline
ltc3217 12 3217f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2005 lt/tp 0805 500 ?printed in usa related parts part number description comments lt 1618 constant current, constant voltage, 1.4mhz up to 16 white leds, v in : 1.6v to 18v, v out(max) = 34v, i q = 1.8ma, high efficiency boost regulator i sd 1 a, 10-lead ms package ltc1911-1.5 250ma (i out ), 1.5mhz high efficiency 75% efficiency, v in : 2.7v to 5.5v, v out(max) = 1.5v/1.8v, i q = 180 a, step-down charge pump i sd 10 a, ms8 package lt1932 constant current, 1.2mhz high efficiency up to 8 white leds, v in : 1v to 10v, v out(max) = 34v, i q = 1.2ma, white led boost regulator i sd 1 a, thinsot tm package lt1937 constant current, 1.2mhz high efficiency up to 4 white leds, v in : 2.5v to 10v, v out(max) = 34v, i q = 1.9ma, white led boost regulator i sd 1 a, thinsot, sc70 packages ltc3200-5 low noise, 2mhz regulated charge pump up to 6 white leds, v in : 2.7v to 4.5v, v out(max) = 5v, i q = 8ma, white led driver i sd 1 a, thinsot package ltc3201 low noise, 1.7mhz regulated charge pump up to 6 white leds, v in : 2.7v to 4.5v, v out(max) = 5v, i q = 6.5ma, white led driver i sd 1 a, 10-lead ms package ltc3202 low noise, 1.5mhz regulated charge pump up to 8 white leds, v in : 2.7v to 4.5v, v out(max) = 5v, i q = 5ma, white led driver i sd 1 a, 10-lead ms package ltc3205 multidisplay led controller 92% efficiency, v in : 2.8v to 4.5v, i q = 50 a, i sd 1 a, (4mm 4mm) qfn package ltc3206 i 2 c multidisplay led controller 92% efficiency, 400ma continuous output current. up to 11 white leds in (4mm 4mm) qfn package ltc3208 high current software configurable multidisplay led 95% efficiency, v in : 2.9v to 4.5v, 1a output current, up to 17 leds for controller 5 displays, (5mm 5mm) qfn package ltc3214 500ma camera led charge pump 93% efficiency, v in : 2.9v to 4.4v, 1x/1.5x/2x boost modes, 3mm 3mm dfn package ltc3215 700ma high current, low noise, white led driver 93% efficiency, v in : 2.9v to 4.4v, 1x/1.5x/2x boost modes, 3mm 3mm dfn package ltc3216 1a high current, low noise, white led driver 93% efficiency, v in : 2.9v to 4.4v, 1x/1.5x/2x boost modes, independent low/high current programming, 3mm 4mm dfn package ltc3251 500ma (i out ), 1mhz to 1.6mhz spread spectrum 85% efficiency, v in : 3.1v to 5.5v, v out : 0.9v to 1.6v, i q = 9 a, step-down charge pump i sd 1 a, 10-lead ms package ltc3405/ltc3405a 300ma (i out ), 1.5mhz synchronous 95% efficiency, v in : 2.7v to 6v, v out(min) = 0.8v, i q = 20 a, step-down dc/dc converter i sd 1 a, thinsot package ltc3406/ltc3406a 600ma (i out ), 1.5mhz synchronous 95% efficiency, v in : 2.7v to 5.5v, v out(min) = 0.6v, i q = 20 a, step-down dc/dc converter i sd 1 a, thinsot package thinsot is a trademark of linear technology corporation. typical applicatio u 500ma camera flash with pwm brightness control c2 2.2 f c3 2.2 f c1 1khz pwm (5% to 100% dc) 2.2 f c4 2.2 f v bat 3.92k 1% i led 500ma (max) 3217 ta02 led1 led2 led3 led4 gnd v bat nc en1 en2 ltc3217 c1p c1m c2p c2m i set1 i set2 cpo

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