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ltc3210 3210fb features description a pp lications t ypical a pplication main/cam led controller in 3mm 3mm qfn the ltc ? 3210 is a low noise charge pump dc/dc converter designed to drive four main leds and one high current cam led for camera lighting. the ltc3210 requires only four small ceramic capacitors and two current set resis- tors 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 main and cam full-scale current settings are programmed by two external resistors. shutdown mode and current output levels are selected via two logic inputs. the full-scale current through the leds is programmed via external resistors. enm and enc are toggled to adjust the led currents via internal counters and dacs. the part is shut down when both enm and enc are low for 150s (typ). 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 en- ter dropout. the ltc3210 is available in a 3mm 3mm 16-lead qfn package. c1p c1m c2p rm rc gnd c2m cpo mled1 mled2 mled3 mled4 cled enm enc v bat ltc3210 v bat c1 2.2f c2 2.2f c3 2.2f 30.1k 1% 24.3k 1% enm enc c4 2.2f 3210 ta01 main cam n low noise charge pump provides high efficiency with automatic mode switching n multimode operation: 1x, 1.5x, 2x n individual full-scale current set resistors n up to 500ma total output current n single wire en/brightness control for main and cam leds (8 brightness steps) n 64:1 brightness control range for main display n four 25ma low dropout main led outputs n one 400ma low dropout cam led output n low noise constant frequency operation* n low shutdown current: 3a n internal soft-start limits inrush current during startup and mode switching n open/short led protection n no inductors n 3mm 3mm 16-lead plastic qfn package v bat (v) 3.0 efficiency (p led /p in ) (%) 60 80 100 3210 ta01b 40 20 50 70 90 30 10 0 3.6 3.8 3.2 4.0 3.4 4.44.2 4 leds at 9ma/led (typ v f at 9ma = 3v, nichia nscw100) t a = 25c 4-led main display efficiency vs v bat voltage n multi-led light supply for cellphones/dscs/pdas l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. *protected by u.s. patents including 6411531.
ltc3210 3210fb e lectrical c haracteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c.v bat = 3.6v, c1 = c2 = c3 = c4 = 2.2f, rm = 30.1k, rc = 24.3k, enm = high, unless otherwise noted. parameter conditions min typ max units v bat operating voltage l 2.9 4.5 v i vbat operating current i cpo = 0, 1x mode, mled lsb setting i cpo = 0, 1.5x mode i cpo = 0, 2x mode 0.375 2.5 4.5 ma ma ma v bat shutdown current enm = enc = low l 3 6 a mled1, mled2, mled3, mled4 current led current ratio (i mled /i rm ) i mled = full scale l 463 515 567 a/a led dropout voltage mode switch threshold, i mled = full scale 100 mv led current matching any two outputs, i mled = full scale 1 % mled current, 3-bit exponential dac 1 enm strobe (fs) 2 enm strobes 3 enm strobes 4 enm strobes 5 enm strobes 6 enm strobes 7 enm strobes (fs/64) 20 10 5 2.5 1.25 0.625 0.312 ma ma ma ma ma ma ma p in c on f iguration 16 15 14 13 5 6 7 8 top view ud package 16-lead (3mm s 3mm) plastic qfn 9 10 17 11 12 4 3 2 1c1p cpo enm mled1 gnd cled enc rc c2p v bat c1m c2m mled2 mled3 mled4 rm t jmax = 125c, q ja = 68c/w exposed pad (pin 17) is gnd, must be soldered to pcb o r d er i n f ormation lead free finish tape and reel part marking package description temperature range ltc3210eud#pbf ltc3210eud#trpbf lbxh 16-lead (3mm s 3mm) plastic qfn C40c to 85c consult ltc marketing for parts specified with wider operating temperature ranges. consult ltc marketing for information on non-standard lead based finish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ (note 1) v bat , cpo to gnd ........................................ C 0.3v to 6v enm, enc ...................................C 0.3v to (v bat + 0.3v) i cpo (note 2) ....................................................... 600ma i mled1- 4 .................................................................30ma i cled (note 2)...................................................... 450ma cpo short-circuit duration .............................. indefinite operating temperature range (note 3) ...C 40c to 85c storage temperature range .................. C 65c to 125c a bsolute m aximum r atings
ltc3210 3210fb the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c.v bat = 3.6v, c1 = c2 = c3 = c4 = 2.2f, rm = 30.1k, rc = 24.3k, enm = high, unless otherwise noted. note 3: the ltc3210e is guaranteed to meet performance specifications from 0c to 85c. specifications over the C 40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 4: 1.5x mode output impedance is defined as (1.5v bat C v cpo )/i out . 2x mode output impedance is defined as (2v bat C v cpo )/i out . note 5: if the part has been shut down then the initial enable time is about 100s longer due to the bandgap enable time. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: based on 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. parameter conditions min typ max units unused mled detection test current mled tied to cpo l 4 16 a threshold voltage v cpo C v mled l 0.5 1.5 v cled current led current ratio (i cled /i rc ) i cled = full scale l 6750 7500 8250 a/a led dropout voltage mode switch threshold, i cled = full scale 500 mv cled current, 3-bit linear dac 1 enc strobe (fs) 7 enc strobes (fs/7) 380 54 ma ma charge pump (cpo) 1x mode output voltage i cpo = 0ma v bat v 1.5x mode output voltage i cpo = 0ma 4.55 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 4) 3.15 2x mode output impedance v bat = 3.2v, v cpo = 5.1v (note 4) 3.95 clock frequency 0.8 mhz mode switching delay 0.4 ms cpo short circuit detection threshold voltage l 0.4 1.3 v test current cpo = 0v, enm = enc = low l 10 30 ma enc, enm v il l 0.4 v v ih l 1.4 v i ih enm = enc = 3.6v l 10 15 20 a i il enm = enc = 0v l C1 1 a enc, enm timing t pw minimum pulse width l 60 ns t sd low time to shutdown (enc and enm = low) l 50 150 250 s t en current source enable time (enc or enm = high) (note 5) l 50 150 250 s rm, rc v rm , v rc l 1.16 1.20 1.24 v i rm , i rc l 70 a electrical characteristics
ltc3210 3210fb temperature (c) ?40 0.40 switch resistance () 0.45 0.50 0.55 0.60 0.65 0.70 ?15 10 35 60 3210 g05 85 i cpo = 200ma v bat = 3.3v v bat = 3.9v v bat = 3.6v temperature (c) ?40 3.4 3.6 3.8 60 3210 g06 3.2 3.0 ?15 10 35 85 2.8 2.6 2.4 open loop output resistance () v bat = 3v v cpo = 4.2v c2 = c3 = c4 = 2.2f load current (ma) 0 3.6 cpo voltage (v) 3.8 4.0 4.2 4.4 4.6 4.8 100 200 300 400 3210 g07 500 c2 = c3 = c4 = 2.2f v bat = 3v v bat = 3.1v v bat = 3.2v v bat = 3.6v v bat = 3.3v v bat = 3.4v v bat = 3.5v temperature (c) ?40 4.2 4.4 4.6 60 3210 g08 4.0 3.8 ?15 10 35 85 3.6 3.4 3.2 open loop output resistance () v bat = 3v v cpo = 4.8v c2 = c3 = c4 = 2.2f load current (ma) 0 cpo voltage (v) 4.8 5.0 5.2 400 3210 g09 4.6 4.4 4.7 4.9 5.1 4.5 4.3 4.2 100 200 300 500 c2 = c3 = c4 = 2.2f v bat = 3v v bat = 3.1v v bat = 3.2v v bat = 3.3v v bat = 3.4v v bat = 3.5v v bat = 3.6v dropout time from shutdown dropout time when enabled 1.5x cpo ripple 2x cpo ripple 1x mode switch resistance vs temperature 1.5x mode charge pump open-loop output resistance vs temperature (1.5v bat ? v cpo )/i cpo 1.5x mode cpo voltage vs load current 2x mode charge pump open-loop output resistance vs temperature (2v bat ? v cpo )/i cpo 2x mode cpo voltage vs load current t a = 25c unless otherwise stated. 500s/div cpo 1v/div en 2v/div 3210 g01 1.5x 2x 1x mode reset 250s/div cpo 1v/div enc 2v/div 3210 g02 1.5x 2x 1x mode reset enm = high 500ns/div v cpo 50mv/div ac-coupled 3210 g03 v bat = 3.6v i cpo = 200ma c cpo = 2.2f 500ns/div v cpo 20mv/div ac-coupled 3210 g04 v bat = 3.6v i cpo = 200ma c cpo = 2.2f t ypical p er f ormance c haracteristics
ltc3210 3210fb mled pin current (ma) 0 mled pin dropout voltage (mv) 60 80 100 16 3210 g11 40 20 50 70 90 30 10 0 42 86 12 14 18 10 20 v bat = 3.6v cled pin current (ma) 50 100 0 cled pin dropout voltage (mv) 200 500 150 250 300 3210 g10 100 400 300 200 350 400 v bat = 3.6v v bat voltage (v) 2.7 760 frequency (khz) 770 790 800 810 3.9 850 3210 g12 780 3.3 3.0 4.2 3.6 4.5 820 830 840 t a = 25c t a = ?40c t a = 85c v bat voltage (v) 2.7 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 3.6 4.2 3210 g13 3.0 3.3 3.9 4.5 v bat shutdown current (a) t a = 25c t a = ?40c t a = 85c v bat voltage (v) 2.7 600 v bat current (a) 640 680 720 3.0 3.3 3.6 3.9 3210 g14 4.2 760 800 620 660 700 740 780 4.5 rm = 33.2k rc = 24.3k load current (ma) 0 supply current (ma) 10 15 400 3210 g15 5 0 100 200 300 500 20 v bat = 3.6v load current (ma) 0 supply current (ma) 10 15 400 3210 g16 5 0 100 200 300 500 20 v bat = 3.6v cled pin voltage (v) 0 cled pin current (ma) 240 320 400 0.8 3210 g17 160 80 200 280 360 120 40 0 0.2 0.4 0.6 1 v bat = 3.6v cled pin dropout voltage vs cled pin current mled pin dropout voltage vs mled pin current oscillator frequency vs v bat voltage v bat shutdown current vs v bat voltage 1x mode no load v bat current vs v bat voltage 1.5x mode supply current vs i cpo (iv bat C 1.5i cpo ) 2x mode supply current vs i cpo (iv bat C 2i cpo ) cled pin current vs cled pin voltage t a = 25c unless otherwise stated. typical per f ormance characteristics
ltc3210 3210fb v bat (v) 2.9 0 efficiency (p led /p in ) (%) 10 30 40 50 3.8 3.95 4.1 4.25 90 3210 g21 20 3.05 3.2 3.35 3.5 3.65 4.4 60 70 80 300ma led current (typ v f at 300ma = 3.1v, aot-2015hpw t a = 25c number of enm strobe pulses 0 0 mled current (ma) 2 6 8 10 20 14 6 4 3 3210 g20 4 16 18 12 7 5 2 1 v bat = 3.6v rm = 33.2k number of enc strobe pulses 0 cled current (ma) 350 5 3210 g19 200 100 7 6 4 50 0 400 300 250 150 3 2 1 v bat = 3.6v rc = 24.3k cled current vs enc strobe pulses mled current vs enm strobe pulses efficiency vs v bat voltage t a = 25c unless otherwise stated. mled pin current vs mled pin voltage mled pin voltage (v) 0.00 mled pin current (ma) 6 18 20 22 0.04 0.08 0.12 3210 g18 2 14 10 4 16 0 12 8 0.02 0.06 0.16 0.20 0.10 0.14 0.18 v bat = 3.6v typical per f ormance characteristics
ltc3210 3210fb c1p, c2p, c1m, c2m (pins 1, 16, 14, 13): charge pump flying capacitor pins. a 2.2f x7r or x5r ceramic ca- pacitor 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 enm and enc inputs. a 2.2f x5r or x7r ceramic capacitor should be connected to ground. enm, enc (pins 3, 10): inputs. the enm and enc pins are used to program the led output currents. each input is strobed up to 7 times to decrement the internal 3-bit dacs from full-scale to 1lsb. the counter will stop at 1 lsb if the strobing continues. the pin must be held high after the final desired positive strobe edge. the data is transferred after a 150s (typ) delay. holding the enm or enc pin low will set the led current to 0 and will reset the counter after 150s (typ). if both inputs are held low for longer than 150s (typ) the part will go into shutdown. the charge pump mode is reset to 1x whenever enc goes low or when the part is in shutdown mode. mled1, mled2, mled3, mled4 (pins 4, 5, 6, 7): outputs. mled1 to mled4 are the main current source outputs. the leds are connected between cpo (anodes) and mled1-4 (cathodes). the current to each led output is set via the enm input, and the programming resistor connected between rm and gnd. each of the four led outputs can be disabled by connecting the output directly to cpo. a 10a current will flow through each directly connected led output. rm, rc (pins 8, 9): led current programming resistor pins. the rm and rc pins will servo to 1.2v. resistors connected between each of these pins and gnd are used to set the cled and mled current levels. connecting a resistor 12k or less will cause the ltc3210 to enter overcurrent shutdown. cled (pin 11): output. cled is the cam current source output. the led is connected between cpo (anode) and cled (cathode). the current to the led output is set via the enc input, and the programming resistor connected between rc and gnd. gnd (pin 12): ground. this pin should be connected to a low impedance ground plane. v bat (pin 15): supply voltage. this pin should be bypassed with a 2.2f, 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. p in functions
ltc3210 3210fb c1p ? + ? + c2m c1m c2p 800khz oscillator timer charge pump 1.215v 3-bit exponential dac mled current sources enable main ? + timer timer 1.215v 3-bit down counter 3-bit down counter 3-bit linear dac cled current source enable cam shutdown gnd cpo mled1 mled2 mled3 mled4 cled enc rc enm rm v bat enable cp 3210 bd 1 15 8 3 9 10 4 14 16 13 12 2 4 5 6 7 11 250k 500 500 250k b lock diagram
ltc3210 3210fb power management the ltc3210 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 ltc3210 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 ltc3210 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 4.6v. any subsequent dropout will cause the part to enter the 2x mode. the cpo voltage will attempt to reach 2x v bat up to 5.1v. the part will be reset to 1x mode whenever the part is shut down or when enc goes low. a two phase nonoverlapping 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 800khz. led current control the mled currents are delivered by the four programmable current sources. eight current settings (0ma to 20ma, rm = 30.1k) are available by strobing the enm pin. each positive strobe edge decrements a 3-bit down counter which controls an exponential dac. when the desired figure 1. current programming and shutdown timing diagram current is achieved enm is stopped high. the output cur- rent then changes to the programmed value after 150s (typ). the counter will stop when the lsb is reached. the output current is set to 0 when enm is toggled low after the output has been enabled. if strobing is started within 150s (typ), after enm has been set low, the counter will continue to count down. after 150s (typ) the counter is reset. the cled current is delivered by a programmable current source. eight linear current settings (0ma to 380ma, rc = 24.3k) are available by strobing the enc pin. each posi- tive strobe edge decrements a 3-bit down counter which controls a 3-bit linear dac. when the desired current is reached, enc is stopped high. the output current then changes to the programmed value after 150s (typ). the counter will stop when the lsb is reached. the output current is set to 0 when enc is toggled low after the output has been enabled. if strobing is started within 150s (typ) after enc has been set low, the counter will continue to count down. after 150s (typ) the counter is reset. the full-scale output current is calculated as follows: mled full-scale output current = ( 1.215v/(rm + 500) ) ? 515 cled full-scale output current = ( 1.215v/(rc + 500) ) ? 7500 when both enm and enc are held low for 150s (typ) the part will go into shutdown. see figure 1 for timing information. enc resets the mode to 1x on a falling edge. t pw 60ns enm = enc = low shutdown t en 150s (typ) t sd 150s (typ) programmed current enm or enc led current 3210 f01 o peration
ltc3210 0 3210fb figure 2. charge pump thevenin-equivalent circuit soft-start initially, when the part is in shutdown, a weak switch connects v bat to cpo. this allows v bat to slowly charge the cpo output capacitor to prevent large charging currents. the ltc3210 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 150s. 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. table 1. charge pump output regulation voltages charge pump mode regulated v cpo 1.5x 4.55v 2x 5.05v when the ltc3210 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 resistance, r ol (figure 2). r ol is dependent on a number of factors including the switching term, 1/(2f osc ? c fly ), internal switch resistances and the nonoverlap 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 C cpo for 1.5x mode and 2v bat C cpo for 2x mode. consider + ? r ol cpo 1.5v bat or 2v bat + ? temperature (?c) ?40 3.4 3.6 3.8 60 3210 f03 3.2 3.0 ?15 10 35 85 2.8 2.6 2.4 open loop output resistance () v bat = 3v v cpo = 4.2v c2 = c3 = c4 = 2.2f figure 3. typical 1.5x r ol vs temperature 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 C 3.8v C 0.1v or 750mv. notice that if the input voltage is raised to 3.2v, the advantage voltage jumps to 900mv a 20% improvement in available strength. from figure 2, for 1.5x mode the available current is given by: i v v r out bat cpo ol = ( . ? ) 1 5 for 2x mode, the available current is given by: i v v r out bat cpo ol = ( ? ) 2 notice that the advantage voltage in this case is 3.1v ? 2 C 3.8v C 0.1v = 2.3v. r ol is higher in 2x mode but a sig- nificant overall increase in available current is achieved. typical values of r ol as a function of temperature are shown in figure 3 and figure 4. shutdown current in shutdown mode all the circuitry is turned off and the ltc3210 draws a very low current from the v bat supply. furthermore, cpo is weakly connected to v bat . the ltc3210 enters shutdown mode when both the enm and enc pins are brought low for 150s (typ). enm and enc have 250k internal pull down resistors to define the shutdown state when the drivers are in a high imped- ance state. operation
ltc3210 3210fb temperature (?c) ?40 4.2 4.4 4.6 60 3210 f04 4.0 3.8 ?15 10 35 85 3.6 3.4 3.2 open loop output resistance () v bat = 3v v cpo = 4.8v c2 = c3 = c4 = 2.2f figure 4. typical 2x r ol vs temperature sources and charge pump until the die has cooled by about 15c. this thermal cycling will continue until the fault has been corrected. mode switching the ltc3210 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 drop-out detection to mode switching is typically 0.4ms. the part is reset back to 1x mode when the part is shut down (enm = enc = low) or on the falling edge of enc. 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. operation thermal protection the ltc3210 has built-in overtemperature protection. at internal die temperatures of around 150c thermal shutdown will occur. this will disable all of the current a pplications i n f ormation v bat , cpo capacitor selection the style and value of the capacitors used with the ltc3210 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: v i f c ripple p p out sc cpo ( ) ( ? ) ? = 3 0 (3) where f osc is the ltc3210 oscillator frequency or typically 800khz 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 ltc3210. as shown in the block diagram, the ltc3210 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 1.3f of capacitance over all conditions. in addition, excessive output capacitor esr >100m will tend to degrade the loop stability. multilayer ceramic chip capacitors typically have exceptional esr performance and when combined 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 ltc3210s input current will be relatively constant while the charge pump is either in the input charging phase or the output charging
ltc3210 3210fb example, over rated voltage and temperature conditions, a 1f, 10v, y5v ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22f, 10v, x7r available in the same case. the capacitor manufacturers 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 the high switching frequency and the transient currents produced by the ltc3210, 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 high edge rate waveforms. the large dv/dt on these pins can couple energy capacitively to adjacent pcb runs. mag- netic fields can also be generated if the flying capacitors are not close to the ltc3210 (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 ltc3210 pins. for a high quality ac ground, it should be returned to a solid ground plane that extends all the way to the ltc3210. the following guidelines should be followed when design- ing a pcb layout for the ltc3210: ? the exposed pad should be soldered to a large cop- per plane that is connected to a solid, low impedance ground plane using plated through-hole vias for proper heat sinking and noise protection. ? input and output capacitors must be placed close to the part. v bat gnd ltc3210 3210 f05 figure 5. 10nh inductor used for input noise reduction (approximately 1cm of board trace) applications in f ormation phase but will drop to zero during the clock nonoverlap times. since the nonoverlap time is small (~35ns), these missing notches 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 ltc3210 through a very small series inductor as shown in figure 5. 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. flying capacitor selection warning: polarized capacitors such as tantalum or aluminum should never be used for the flying capaci- tors since their voltage can reverse upon start-up of the ltc3210. 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 1.6f of capacitance for each of the flying capacitors. capacitors of different materials lose their capacitance with higher temperature and voltage at different rates. for example, a ceramic capacitor made of x7r material will retain most of its capacitance from C 40c to 85c whereas a z5u or y5v style capacitor will lose considerable capacitance over that range. 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 capacitance for a given case size rather than comparing the specified capacitance value. for
ltc3210 3210fb ? 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. ? v bat , cpo traces must be wide to minimize inductance and handle high currents. ? led pads must be large and connected to other layers of metal to ensure proper heat sinking. ? rm and rc pins are sensitive to noise and capacitance. the resistors should be placed near the part with mini- mum line width. 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 represents 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 the efficiency of the ltc3210 depends upon the mode in which it is operating. recall that the ltc3210 operates as a pass switch, connecting v bat to cpo, until dropout is detected at the led pin. this feature provides the op- timum 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 v i v i v v led in led led bat bat led bat ( ? ) ( ? ) since the input current will be very close to the sum of the led currents. at moderate to high output power, the quiescent current of the ltc3210 is negligible and the expression above is valid. once dropout is detected at any led pin, the ltc3210 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 v i v i v v = = = ( ? ) ( ? ( . )? ) ( . ? ) 1 5 1 5 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 v i v i v v = = = ( ? ) ( ? ( )? ) ( ? ) 2 2 thermal management for higher input voltages and maximum output current, there can be substantial power dissipation in the ltc3210. if the junction temperature increases above approximately 150c the thermal shut down circuitry will automatically 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. applications in f ormation
ltc3210 3210fb p ackage description 3.00 p 0.10 (4 sides) recommended solder pad pitch and dimensions 1.45 p 0.05 (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 p 0.10 bottom view?exposed pad 1.45 p 0.10 (4-sides) 0.75 p 0.05 r = 0.115 typ 0.25 p 0.05 1 pin 1 notch r = 0.20 typ or 0.25 s 45o chamfer 15 16 2 0.50 bsc 0.200 ref 2.10 p 0.05 3.50 p 0.05 0.70 p0.05 0.00 ? 0.05 (ud16) qfn 0904 0.25 p0.05 0.50 bsc package outline ud package 16-lead plastic qfn (3mm s 3mm) (reference ltc dwg # 05-08-1691)
ltc3210 3210fb 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. r evision h istory rev date description page number b 6/10 update to note 3 3 (revision history begins at rev b)
ltc3210 3210fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com ? linear technology corporation 2006 lt 0610 rev b ? printed in usa r elate d p arts t ypical a pplication 3-led main, one led camera part number description comments lt1618 constant current, 1.4mhz, 1.5a boost converter v in : 1.6v to 18v, v out(max) = 36v, i q = 1.8ma, i sd <1a, ms package ltc3205 250ma, 1mhz, multi-display led controller v in : 2.8v to 4.5v, v out(max) = 5.5v, i q = 50a, i sd <1a, qfn package ltc3206 400ma, 800khz, multi-display led controller v in : 2.8v to 4.5v, v out(max) = 5.5v, i q = 50a, i sd <1a, qfn package ltc3208 high current software configurable multi-display led controller v in : 2.9v to 4.5v, v out = 5.1v, i q = 250a, i sd <1a, 17 current sources (main, sub, rgb, cam, aux), 5 5 qfn package ltc3209-1/ ltc3209-2 600ma main/camera/aux led controller v in : 2.9v to 4.5v, i q = 400a, up to 94% efficiency, 4mm 4mm qfn-20 package ltc3210-1 main/cam led controller with 64-step brightness control v in : 2.9v to 4.5v, i q = 400a, 3-bit dac brightness control for main and cam leds, 3mm 3mm qfn package ltc3214 500ma camera led charge pump v in : 2.9v to 4.5v, single output, 3 3 dfn package ltc3215 700ma low noise high current led charge pump v in : 2.9v to 4.4v, v out(max) = 5.5v, i q = 300a, i sd <2.5a, dfn package ltc3216 1a low noise high current led charge pump with independent flash/torch current control v in : 2.9v to 4.4v, v out(max) = 5.5v, i q = 300a, i sd <2.5a, dfn package ltc3217 600ma low noise multi-led camera light v in : 2.9v to 4.4v, i q = 400a, four 100ma outputs, qfn package ltc3440/ltc3441 600ma/1.2a i out , 2mhz/1mhz, synchronous buck-boost dc/dc converter v in : 2.4v to 5.5v, v out(max) = 5.25v, i q = 25a/50a, i sd <1a, ms/dfn packages ltc3443 600ma/1.2a i out , 600khz, synchronous buck-boost dc/dc converter v in : 2.4v to 5.5v, v out(max) = 5.25v, i q = 28a, i sd <1a, dfn package ltc3453 1mhz, 800ma synchronous buck-boost high power led driver v in(min) : 2.7v to 5.5v, v in(max) : 2.7v to 4.5v, i q = 2.5ma, i sd <6a, qfn package lt3467/lt3467a 1.1a (i sw ), 1.3/2.1mhz, high efficiency step-up dc/dc converters with integrated soft-start v in : 2.4v to 16v, v out(max) = 40v, i q = 1.2ma, i sd <1a, thinsot package lt3479 3a, 42v, 3.5mhz boost converter v in : 2.5v to 24v, v out(max) = 40v, i q = 2a, i sd <1a dfn, tssop packages c1p c1m c2p rm rc gnd c2m cpo mled1 mled2 mled3 mled4 cled enm enc v bat ltc3210 v bat c1 2.2f c4 2.2f c2 2.2f c3 2.2f 30.1k 1% 24.3k 1% enm enc 3210 ta02 main cam mled4 disabled

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